Synbiotics, prebiotics and probiotics for solid organ transplant recipients

Abstract

Background

Solid organ transplantation has seen improvements in both surgical techniques and immunosuppression, achieving prolonged survival. Essential to graft acceptance and post‐transplant recovery, immunosuppressive medications are often accompanied by a high prevalence of gastrointestinal (GI) symptoms and side effects. Apart from GI side effects, long‐term exposure to immunosuppressive medications has seen an increase in drug‐related morbidities such as diabetes mellitus, hyperlipidaemia, hypertension, and malignancy. Non‐adherence to immunosuppression can lead to an increased risk of graft failure.

Recent research has indicated that any microbial imbalances (otherwise known as gut dysbiosis or leaky gut) may be associated with cardiometabolic diseases in the long term. Current evidence suggests a link between the gut microbiome and the production of putative uraemic toxins, increased gut permeability, and transmural movement of bacteria and endotoxins and inflammation. Early observational and intervention studies have been investigating food‐intake patterns, various synbiotic interventions (antibiotics, prebiotics, or probiotics), and faecal transplants to measure their effects on microbiota in treating cardiometabolic diseases. It is believed high doses of synbiotics, prebiotics and probiotics are able to modify and improve dysbiosis of gut micro‐organisms by altering the population of the micro‐organisms. With the right balance in the gut flora, a primary benefit is believed to be the suppression of pathogens through immunostimulation and gut barrier enhancement (less permeability of the gut).

Objectives

To assess the benefits and harms of synbiotics, prebiotics, and probiotics for recipients of solid organ transplantation.

Search methods

We searched the Cochrane Kidney and Transplant Specialised Register up to 9 March 2022 through contact with the Information Specialist using search terms relevant to this review. Studies in the Register are identified through searches of CENTRAL, MEDLINE, and EMBASE, conference proceedings, the International Clinical Trials Register (ICTRP) Search Portal and ClinicalTrials.gov.

Selection criteria

We included randomised controlled trials measuring and reporting the effects of synbiotics, prebiotics, or probiotics, in any combination and any formulation given to solid organ transplant recipients (any age and setting). Two authors independently assessed the retrieved titles and abstracts and, where necessary, the full text to determine which satisfied the inclusion criteria.

Data collection and analysis

Data extraction was independently carried out by two authors using a standard data extraction form. The methodological quality of included studies was assessed using the Cochrane risk of bias tool. Data entry was carried out by one author and cross‐checked by another. Confidence in the evidence was assessed using the Grading of Recommendations Assessment, Development and Evaluation (GRADE) approach.

Main results

Five studies (250 participants) were included in this review. Study participants were adults with a kidney (one study) or liver (four studies) transplant. One study compared a synbiotic to placebo, two studies compared a probiotic to placebo, and two studies compared a synbiotic to a prebiotic.

Overall, the quality of the evidence is poor. Most studies were judged to have unclear (or high) risk of bias across most domains. Of the available evidence, meta‐analyses undertaken were of limited data from small studies. Across all comparisons, GRADE evaluations for all outcomes were judged to be very low certainty evidence. Very low certainty evidence implies that we are very uncertain about results (not estimable due to lack of data or poor quality).

Synbiotics had uncertain effects on the change in microbiota composition (total plasma p‐cresol), faecal characteristics, adverse events, kidney function or albumin concentration (1 study, 34 participants) compared to placebo.

Probiotics had uncertain effects on GI side effects, infection rates immediately post‐transplant, liver function, blood pressure, change in fatty liver, and lipids (1 study, 30 participants) compared to placebo.

Synbiotics had uncertain effects on graft health (acute liver rejection) (2 studies, 129 participants: RR 0.73, 95% CI 0.43 to 1.25; 2 studies, 129 participants; I² = 0%), the use of immunosuppression, infection (2 studies, 129 participants: RR 0.18, 95% CI 0.03 to 1.17; I² = 66%), GI function (time to first bowel movement), adverse events (2 studies, 129 participants: RR 0.79, 95% CI 0.40 to 1.59; I² = 20%), serious adverse events (2 studies, 129 participants: RR 1.49, 95% CI 0.42 to 5.36; I² = 81%), death (2 studies, 129 participants), and organ function measures (2 studies; 129 participants) compared to prebiotics.

Authors' conclusions

This review highlights the severe lack of high‐quality RCTs testing the efficacy of synbiotics, prebiotics or probiotics in solid organ transplant recipients. We have identified significant gaps in the evidence.

Despite GI symptoms and postoperative infection being the most common reasons for high antibiotic use in this patient population, along with increased morbidity and the growing antimicrobial resistance, we found very few studies that adequately tested these as alternative treatments.

There is currently no evidence to support or refute the use of synbiotics, prebiotics, or probiotics in solid organ transplant recipients, and findings should be viewed with caution.

We have identified an area of significant uncertainty about the efficacy of synbiotics, prebiotics, or probiotics in solid organ transplant recipients. Future research in this field requires adequately powered RCTs comparing synbiotics, prebiotics, and probiotics separately and with placebo measuring a standard set of core transplant outcomes. Six studies are currently ongoing (822 proposed participants); therefore, it is possible that findings may change with their inclusion in future updates.

Plain language summary

Synbiotics, prebiotics (dietary fibre) or probiotics (good bacteria) for people with a solid organ transplant

Key messages

People who receive an organ transplant (heart, kidney, liver, lung, or pancreas) experience long‐lasting, severe bowel and gut symptoms after their surgery from the medications (severe diarrhoea, severe constipation, heartburn and reflux, gas, bloating, and stomach cramps).

We believe these medications can cause a change in the gut flora (a change in the balance of the good and bad bacteria) which causes severe bowel symptoms.

To improve the balance of the gut flora, good bacteria can be taken in tablets of high doses of prebiotics and probiotics. Synbiotics are a combination of the two. Some research suggests that taking high doses of the good bacteria can re‐balance the good bacteria in your gut and improve bowel symptoms.

What did we do?

We reviewed all of the evidence on synbiotics, prebiotics and probiotics to see whether they can improve bowel and gut problems in people who have received an organ transplant (heart, kidney, liver, lung, or pancreas).

What did we find?

We found 5 studies randomising 250 participants. One study looked at kidney transplant patients, and four studies looked at liver transplant patients, mostly taking synbiotics, prebiotics or probiotics within a month after surgery. We are uncertain whether probiotics improve bowel and gut side effects or reduce your chance of getting an infection after the surgery. We are uncertain whether these treatments will help stool characteristics, kidney function, or the amount of immunosuppression medications to take.

The quality of the evidence that we found is poor. Three studies were only abstracts (not the full paper and not the full results). All five studies were conducted using moderate to poor quality methods and too few patients.

Summary

Currently, we do not have enough information from trials to know whether synbiotics, prebiotics or probiotics work to improve the recovery in people with a solid organ transplant. Six studies are currently ongoing (822 proposed participants), therefore it is possible that findings may change with the inclusion of these studies in future updates.

The evidence is up to date to 9 March 2022.

Summary of findings

Summary of findings 1. Synbiotics versus placebo for solid organ transplant recipients.

Synbiotics versus placebo for solid organ transplant recipients
Patient or population: adult solid organ transplant recipients (kidney) Settings: hospital (postoperative) Intervention: synbiotics (prebiotics and probiotics combined) Comparison: placebo
Outcomes	Illustrative comparative risks* (95% CI)		Relative effect (95% CI)	No. of participants (studies)	Quality of the evidence (GRADE)
	Assumed risk	Corresponding risk
	Placebo	Synbiotics
GI function	‐	‐	‐	‐	‐
Graft health	‐	‐	‐	‐	‐
Adverse events	‐	‐	‐	‐	‐
Serious adverse events	‐	‐	‐	‐	‐
Death	‐	‐	‐	‐	‐
*The basis for the assumed risk (e.g. the median control group risk across studies) is provided in footnotes. The corresponding risk (and its 95% CI) is based on the assumed risk in the comparison group and the relative effect of the intervention (and its 95% CI). CI: Confidence interval; RR: Risk Ratio
GRADE Working Group grades of evidence High quality: Further research is very unlikely to change our confidence in the estimate of effect. Moderate quality: Further research is likely to have an important impact on our confidence in the estimate of effect and may change the estimate. Low quality: Further research is very likely to have an important impact on our confidence in the estimate of effect and is likely to change the estimate. Very low quality: We are very uncertain about the estimate.

No data were available for meta‐analysis for any of these outcomes

Summary of findings 2. Probiotics versus placebo for solid organ transplant recipients.

Probiotics versus placebo for solid organ transplant recipients
Patient or population: adult solid organ transplant recipients (liver) Settings: hospital (postoperative) Intervention: probiotics Comparison: placebo
Outcomes	Illustrative comparative risks* (95% CI)		Relative effect (95% CI)	No. of participants (studies)	Quality of the evidence (GRADE)
	Assumed risk	Corresponding risk
	Placebo	Probiotics
GI function	‐	‐	‐	‐	‐
Graft health	‐	‐	‐	‐	‐
Adverse events	‐	‐	‐	‐	‐
Serious adverse events	‐	‐	‐	‐	‐
Death	‐	‐	‐	‐	‐
*The basis for the assumed risk (e.g. the median control group risk across studies) is provided in footnotes. The corresponding risk (and its 95% CI) is based on the assumed risk in the comparison group and the relative effect of the intervention (and its 95% CI). CI: Confidence interval; RR: Risk Ratio; GI: gastrointestinal
GRADE Working Group grades of evidence High quality: Further research is very unlikely to change our confidence in the estimate of effect. Moderate quality: Further research is likely to have an important impact on our confidence in the estimate of effect and may change the estimate. Low quality: Further research is very likely to have an important impact on our confidence in the estimate of effect and is likely to change the estimate. Very low quality: We are very uncertain about the estimate.

No data were available for meta‐analysis of any of our outcomes

Summary of findings 3. Synbiotics versus prebiotics for solid organ transplant recipients.

Synbiotics versus prebiotics for solid organ transplant recipients
Patient or population: adult solid organ transplant recipients (liver) Settings: hospital Intervention: synbiotics (prebiotics and probiotics combined) Comparison: prebiotics
Outcomes	Illustrative comparative risks* (95% CI)		Relative effect (95% CI)	No. of participants (studies)	Quality of the evidence (GRADE)
	Assumed risk	Corresponding risk
	Prebiotics	Synbiotics
GI function	‐	‐	‐	‐	‐
Graft health: acute liver rejection Follow‐up: up to 30 days post‐operation	(38 per 1000)	247 per 1000 (146 to 423)	RR 0.73 (95% CI 0.43 to 1.25)	129 (2)	⊕⊝⊝⊝ very low1
Graft health	‐	‐	‐	‐	‐
Adverse events Follow‐up: up to 30 days post‐operation	277 per 1000	219 per 1000 (111 to 440)	RR 0.79 (95% CI 0.40 to 1.59)	129 (2)	⊕⊝⊝⊝ very low1
Serious adverse events Follow‐up: up to 30 days post‐operation	354 per 1000	527 per 1000 (149 to 1000)	RR 1.49 (95% CI 0.42 to 5.36)	129 (2)	⊕⊝⊝⊝ very low1
Death Follow‐up: up to 30 days post‐operation	0 per 1000	0 per 1000	Not estimated	129 (2)	⊕⊝⊝⊝ very low2
*The basis for the assumed risk (e.g. the median control group risk across studies) is provided in footnotes. The corresponding risk (and its 95% CI) is based on the assumed risk in the comparison group and the relative effect of the intervention (and its 95% CI). CI: Confidence interval; RR: Risk Ratio; GI: gastrointestinal
GRADE Working Group grades of evidence High quality: Further research is very unlikely to change our confidence in the estimate of effect. Moderate quality: Further research is likely to have an important impact on our confidence in the estimate of effect and may change the estimate. Low quality: Further research is very likely to have an important impact on our confidence in the estimate of effect and is likely to change the estimate. Very low quality: We are very uncertain about the estimate.

¹ Downgraded twice for risk of bias and once for sparse data from small study sizes

² Downgraded to very low certainty evidence due to sparse single study data that could not be meta‐analysed

No data were available for meta‐analysis for GI function and graft health

Background

Description of the condition

Solid organ transplantation

Solid organ transplantation involves the transplant of a heart, kidney, liver, lung, or pancreas from a living or deceased donor. It is often the only treatment for end‐stage organ failure, particularly for liver and heart failure (WHO 2020). For kidney failure, whilst kidney replacement therapies are common, kidney transplantation is generally accepted as the best treatment both for quality of life (QoL) and cost‐effectiveness (WHO 2020).

Solid organ transplantation is one of the largest therapeutic medical advancements of the 20th century (Linden 2009). Starting from what were clinical experiments, improvements in both surgical techniques and immunosuppression achieved prolonged recipient survival, resulting in transplantation proven to be clinically effective, life‐saving, and cost‐effective (Linden 2009).

The Global Observatory on Donation and Transplantation reported 146,840 organs transplanted annually in 2018, a 5.6% increase over 2017 (GODT 2020). By organ type, 95,479 kidney (64% deceased donors), 34,074 liver (80.5% deceased donors, 0.1% domino), 8,311 heart, 6,475 lung, 2,338 pancreatic, and 163 small bowel transplantations (GODT 2020).

Immunosuppression

To reduce the chance of graft rejection and other complications, immunosuppressive medications are standard post‐transplant treatment. Essential to graft acceptance and effective recovery, doses will vary depending on the age, organ type, and health status of the individual patient. Immunosuppressive medications are often accompanied by a high prevalence of gastrointestinal (GI) symptoms and gut intolerance side effects (Lehto 2018; Luyckx 2018). Apart from GI side effects, long‐term exposure to immunosuppressive medications has seen an increase in drug‐related morbidities such as cardiovascular disease, diabetes mellitus, hyperlipidaemia, hypertension, and malignancy (Sudan 2007). In the paediatric population, children differ in their immune responses, the way they metabolise drugs, and their susceptibility to adverse effects of transplantation and immunosuppression (Sudan 2007). Non‐compliance to immunosuppressive treatments, particularly among adolescents, can lead to an increased risk of graft failure (Sudan 2007).

The gut microbiome

The human microbiome is the collective genomes of the micro‐organisms in a particular environment (Valdes 2018) and is of emerging high interest in chronic disease research. The human gut microbiota includes fungi, bacteria, archaea, protozoa, and viruses that all interact with each other and the host to affect the host's health and physiology (Azad 2018). The human intestine hosts more than 10 billion micro‐organisms of which the microbial composition changes from person to person, along both the digestive tract and within the urinary and kidney environments (Aron‐Wisnewsky 2016). Recent culture‐independent studies that use high‐throughput sequencing have indicated that any microbial imbalances (otherwise known as gut dysbiosis or leaky gut) may be associated with cardiometabolic diseases in the long term (such as allergy, asthma, inflammatory bowel disease, celiac disease, systemic lupus erythematosus, arthritis, chronic kidney disease (CKD), diabetes obesity, and cardiovascular disease (CVD)) (Aron‐Wisnewsky 2016; Bromberg 2015). In people with advanced stages of CKD, uraemia alters the biochemical milieu, promoting disturbances in gut microbiota (the community or micro‐organisms themselves (Valdes 2018) and the intestinal barrier (Mafra 2019). Furthermore, it is reported that around 30% of transplant recipients experience some form of GI side effects during treatment and follow‐up (Bromberg 2015; Lehto 2018.)

Current evidence suggests a link between the gut microbiome and CKD, particularly with respect to the production of putative uraemic toxins (e.g. indoxyl sulfate, p‐cresol sulfate, phenylacetylglutamine, trimethylamine‐N‐oxide, kynurenine), increased gut permeability, and transmural movement of bacteria and endotoxins and inflammation (Beerepoot 2016; Cremon 2018; Lehto 2018; Luyckx 2018).

Description of the intervention

Early observational and intervention studies have investigated food‐intake patterns, various synbiotic interventions (antibiotics, prebiotics, or probiotics), and faecal transplants to measure their effects on microbiota in treating cardiometabolic diseases, in particular CKD (Aron‐Wisnewsky 2016).

Prebiotics

The International Scientific Association for Probiotics and Prebiotics (Gibson 2017) defines prebiotics as substrates, or non‐digestible dietary substances, that are selectively utilised and fermented within the small intestine by host micro‐organisms. Modifying or diversifying the host microbiota may induce a health benefit to the host. Most types of prebiotics are subsets of carbohydrate groups and mostly oligosaccharide carbohydrates (Davani‐Davari 2019).

• Fructans: inulin and fructo‐oligosaccharides (stimulate the enrichment of native probiotics Lactobacilli and Bifidobacteria)

• Galacto‐oligosaccharides (also known as trans‐galacto‐oligosaccharides, stimulate the enrichment of native probiotics Lactobacilli, Bifidobacteria, Enterobacteria, Bacteroidetes, and Firmicutes)

• Starch and glucose‐derived oligosaccharides: resistant starch, polydextrose

• Other oligosaccharides: pectic‐oligosaccharide (from the polysaccharide pectin)

• Non‐carbohydrate oligosaccharides: cocoa‐derived flavanols.

Natural sources of prebiotics can be obtained in peas, beans, cow's milk, human breast milk, soybean, rye, tomato, barley, wheat, honey, banana, onion, chicory, garlic, sugar beet, asparagus, and artichoke.

Probiotics

The term probiotics are used to describe live micro‐organisms that are intended to confer health benefits on the host when administered in adequate quantities (FAO/WHO 2002). The living bacteria may modulate the existing composition of gut microbiota in an attempt to improve the health of the GI tract, the immune system, inflammatory state and the "bioavailability of micronutrients" (Cremon 2018). The key microbial organisms often found in probiotic treatments are:

• Lactobacillus

• Bifidobacterium

• Saccharomyces

• Streptococcus

• Enterococcus

• Escherichia

• Bacillus

Natural sources of probiotics can be obtained in fermented foods such as yoghurt, kimchi, kombucha, sauerkraut, miso, pickles, raw apple cider vinegar, kefir, tempeh, some cheeses, and some sourdough breads.

Synbiotics

Synbiotics are the combination of prebiotics and probiotics in one treatment with the intention of producing a superior effect compared to either agent alone (Pan 2018). The effect is currently unknown.

Synthetic versions of synbiotics, prebiotics, and probiotics are available as oral capsules, tablets, liquids, or powder forms over the counter in most developed countries (Cremon 2018).

How the intervention might work

It is believed through growing research that high doses of synbiotics, prebiotics, and probiotics are able to modify and improve dysbiosis of gut micro‐organisms by altering the population of the micro‐organisms. There is increasing research that suggests with the right balance in the gut flora, a primary benefit is (believed to be) the suppression of pathogens through immunostimulation and gut barrier enhancement (less permeability of the gut) (Cremon 2018).

The gut microbiota ferments prebiotics and produces short‐chain fatty acids (lactic acid, butyric acid, propionic acid), which have positive effects on the airways, dendritic cells in bone marrows, and decreases the pH of the colon (Davani‐Davari 2019). Prebiotics also decrease the gut pH resulting in the butyrogenic effect ‐ where a slight change in the unit of change in pH alters the entire composition or population of acid‐sensitive species (Bacterioids) and promotes butyrate formation of Firmicutes (Davani‐Davari 2019).

Probiotics alter the intestinal pH, inhibit pathogens (via the generation of antibacterial compounds, competitively eliminating pathogens in receptor binding sites and competing for available nutrients), inhibit mutagenic and carcinogenic production, and maintain the intestinal barrier (Kato 2008).

Why it is important to do this review

Prebiotics and probiotics are freely available as over‐the‐counter purchases in most developed countries and are being used as therapeutic supplements for improving the function and balance of gut microbiota in the general population. Whilst many positive effects have been identified, the exact mechanism of action by which these compounds exert their beneficial actions in humans is only partially understood (Cremon 2018). In the general population, there is no definitive data to support the use of synbiotics, prebiotics, or probiotics. In solid organ transplant populations, there are uncertain effects because of potential immunosuppressive effects and the risk of catastrophic infections with live micro‐organisms. The efficacy of these interventions and the certainty of the evidence in these patients remains unknown; thus, it is imperative to synthesise the benefits and harms associated with these treatments.

Objectives

This review aimed to look at the benefits and harms of synbiotics, prebiotics, and probiotics for people with a solid organ transplantation.

Methods

Criteria for considering studies for this review

Types of studies

All randomised controlled trials (RCTs) and quasi‐RCTs (RCTs in which allocation to treatment was obtained by alternation, use of alternate medical records, date of birth or other predictable methods) and cluster RCTs. Cross‐over studies were eligible, and data from the first phase only was to be used for analysis.

Studies in any healthcare setting were included.

Excluded study design: single‐arm studies, commentaries, editorials, and clinical observations.

Types of participants

Inclusion criteria

• Adults and children with a solid organ transplant (heart, kidney, liver, lung, pancreas, or intestinal/short bowel)

• Single or multiple transplants

• Transplant from a living or deceased donor

• Studies of populations with altered GI function and co‐morbidities (such as diabetic kidney disease) were to be included but analysed as subgroups.

Exclusion criteria

• Adults and children who have signs of systemic illness (such as fever, loin pain, toxicity).

Types of interventions

• Any synbiotic

• Any prebiotic

• Any probiotic

• Combination therapies of biotics with other biotic, pharmacological, or non‐pharmacological treatments

• Any dose, duration, administration, or frequency

• Any formulation: tablet, capsule, or powder

Participants receiving concurrent pharmacological medications for co‐morbidities such as blood glucose medications, blood pressure (BP) medications, and immunosuppressants were included, but we planned to analyse as subgroups.

Studies of high‐dose prebiotics for the purpose of purgation and studies of dietary changes were excluded.

Comparison pairs for analysis

• A synbiotic, prebiotic, or probiotic treatment compared to placebo

• A synbiotic, prebiotic, or probiotic treatment compared to no treatment

• A synbiotic, prebiotic, or probiotic treatment compared to another synbiotic, prebiotic, or probiotic treatment (A versus B)

• A synbiotic, prebiotic, or probiotic treatment compared to a pharmacological comparator (antibiotics, immunosuppressants, other medicines)

• A synbiotic, prebiotic, or probiotic treatment compared to a non‐pharmacological comparator (dietary, educational, behavioural, vitamin or herbal supplements, Traditional Chinese Medicine)

• Combinations of synbiotic, prebiotic or probiotic treatment with another biotic, another pharmacological, or another non‐pharmacological treatment compared to any of the above comparators

For each comparison, synbiotics, prebiotics, and probiotics were planned to be analysed as separate comparisons.

Dose, frequency, and duration were planned to be analysed as separate comparisons.

Formulations were planned to be analysed as subgroups.

Types of outcome measures

This review did not exclude studies based on non‐reporting of outcomes of interest.

The outcomes selected include the relevant SONG core outcome sets as specified by the Standardised Outcomes in Nephrology initiative (SONG 2017).

Primary outcomes

• GI function: change in any GI upset or intolerance; microbiota composition; faecal characteristics (such as the Bristol Stool Chart) (Lewis 1997); colonic transit time

• Graft health: organ rejection, organ acceptance, graft infection

• QoL issues: using any validated QoL scale

• Adverse events and serious adverse events

• Death and cause‐specific death

Secondary outcomes

• BP: systolic (SBP), diastolic (DBP)

• Organ function measures

  • Cardiac function: echocardiogram

  • Kidney function: creatinine clearance, serum creatinine, albuminuria, proteinuria, dialysis, estimated glomerular filtration rate (eGFR)

  • Liver function measures: alanine transaminase (ALT); aspartate aminotransferase (AST); alkaline phosphatase (ALP); albumin; bilirubin

  • Pulmonary function: peak expiratory flow (PEF); arterial blood gas; forced vital capacity (FVC); forced expiratory volume in one second (FEV1); forced expiratory ratio (FEV); FEV1/FVC

  • Pancreas function measures

• Relapse

• Pain: using any validated pain scale

• Patient satisfaction and convenience of treatment

• Treatment adherence

• Use of immunosuppressants

• CVD

  • CVD markers: BP; lipids; vascular access; left ventricular mass index; peripheral vascular disease; cerebrovascular disease; coronary artery disease

  • CVD events: stroke, MI, heart failure, transient ischaemic attack

• Cancer

• Infection

• Life participation: return to normal activities; days absent from work/school; mental health and functional status

Search methods for identification of studies

Electronic searches

We searched the Cochrane Kidney and Transplant Register of Studies up to 9 March 2022 through contact with the Information Specialist using search terms relevant to this review. The Register contains studies identified from the following sources:

1. Monthly searches of the Cochrane Central Register of Controlled Trials (CENTRAL)

2. Weekly searches of MEDLINE OVID SP

3. Kidney and transplant journals and the proceedings and abstracts from major kidney and transplant conferences

4. Searching the current year of EMBASE OVID SP

5. Weekly current awareness alerts for selected kidney and transplant journals

6. Searches of the International Clinical Trials Register (ICTRP) Search Portal and ClinicalTrials.gov.

Studies contained in the Register are identified through searches of CENTRAL, MEDLINE, and EMBASE based on the scope of Cochrane Kidney and Transplant. Details of search strategies, as well as a list of handsearched journals, conference proceedings and current awareness alerts, are available on the Cochrane Kidney and Transplant website.

See Appendix 1 for search terms used in strategies for this review.

Searching other resources

1. Reference lists of review articles, relevant studies, and clinical practice guidelines.

2. Contacting relevant individuals/organisations seeking information about unpublished or incomplete studies.

3. Grey literature sources (e.g. abstracts, dissertations, and theses), in addition to those already included in the Cochrane Kidney and Transplant Register of Studies, will not be searched.

Data collection and analysis

Selection of studies

The search strategy described was used to obtain titles and abstracts of studies that may be relevant to the review. The titles and abstracts were screened independently by two authors, who discarded studies that were not applicable; however, studies and reviews that might include relevant data or information on studies were retained initially. Two authors independently assessed the retrieved abstracts and, if necessary, the full text of these studies to determine which studies satisfy the inclusion criteria. Disagreements were resolved in consultation with a third author.

Data extraction and management

Data extraction was carried out independently by two authors using standard data extraction forms. Disagreements were resolved in consultation with a third author. Studies reported in non‐English language journals were planned to be translated before assessment. Where more than one publication of one study existed, reports were grouped together, and the publication with the most complete data will be used in the analyses. Where relevant outcomes were only published in earlier versions, these data were used. Any discrepancy between published versions was planned to be highlighted.

Assessment of risk of bias in included studies

The following items were independently assessed by two authors using the Cochrane risk of bias assessment tool (Higgins 2020) (see Appendix 2).

• Was there adequate sequence generation (selection bias)?

• Was allocation adequately concealed (selection bias)?

• Was knowledge of the allocated interventions adequately prevented during the study?

  • Participants and personnel (performance bias)

  • Outcome assessors (detection bias)

• Were incomplete outcome data adequately addressed (attrition bias)?

• Are reports of the study free of suggestion of selective outcome reporting (reporting bias)?

• Was the study apparently free of other problems that could put it at risk of bias?

Measures of treatment effect

For dichotomous outcomes (e.g. death), results were to be expressed as risk ratio (RR) with 95% confidence intervals (CI). Where continuous scales of measurement were used to assess the effects of treatment (e.g. BP), the mean difference (MD) or the standardised mean difference (SMD) if different scales have been used were planned. Where possible, we planned to use the mean change score from the baseline. We anticipated that some studies may only report the mean endpoint score of which we planned to use the final time point available.

Unit of analysis issues

We only accepted randomisation of the individual participant. For multiple‐dose studies, we used data for the first dose only. For cross‐over studies, we planned to use data from the first phase only.

Dealing with missing data

Any further information required from the original author was requested by written correspondence (e.g. emailing to corresponding author/s), and any relevant information obtained in this manner was planned to be included in the review. However, no such data were obtained. Evaluation of important numerical data such as screened, randomised patients, as well as intention‐to‐treat, as‐treated and per‐protocol population, was planned to be carefully performed. Attrition rates, for example, drop‐outs, losses to follow‐up and withdrawals were investigated. Issues of missing data and imputation methods (for example, last‐observation‐carried‐forward) were critically appraised (Higgins 2020).

Assessment of heterogeneity

We first planned to assess the heterogeneity by visual inspection of the forest plot. We planned to quantify statistical heterogeneity using the I² statistic, which describes the percentage of total variation across studies that is due to heterogeneity rather than sampling error (Higgins 2003). A guide to the interpretation of I² values was as follows.

• 0% to 40%: might not be important

• 30% to 60%: may represent moderate heterogeneity

• 50% to 90%: may represent substantial heterogeneity

• 75% to 100%: considerable heterogeneity.

The importance of the observed value of I² depends on the magnitude and direction of treatment effects and the strength of evidence for heterogeneity (e.g. P‐value from the Chi² test or a confidence interval for I²) (Higgins 2020).

Assessment of reporting biases

If possible, funnel plots were planned to be used to assess the potential existence of small study bias (Higgins 2020).

Data synthesis

Data were planned to be pooled using the random‐effects model, but the fixed‐effect model was also to be used to ensure the robustness of the model chosen and susceptibility to outliers.

Subgroup analysis and investigation of heterogeneity

Subgroup analyses were planned to be used to explore possible sources of heterogeneity (e.g. participants, interventions, and study quality). Heterogeneity among participants could be related to age, co‐morbidities, and disease pathology. Heterogeneity in treatments could be related to prior agent(s) used and the agent, dose, and duration of therapy. Adverse effects were tabulated and assessed with descriptive techniques, as they were likely to be different for the various agents used. Where possible, the risk difference with 95% CI was planned to be calculated for each adverse effect, either compared to no treatment or to another agent.

Planned subgroups, if sufficient data were available, were as follows.

• Disease stage

• Participants with co‐morbidities

• Concurrent pharmacological medications

• Type of formulation of biotics

• Age: children, adults

• Level of GI function of GI issues

Sensitivity analysis

We planned to perform sensitivity analyses in order to explore the influence of the following factors on effect size.

• Repeating the analysis, excluding unpublished studies

• Repeating the analysis taking into account the risk of bias, as specified

• Repeating the analysis, excluding any very long or large studies to establish how much they dominate the results

• Repeating the analysis excluding studies using the following filters: diagnostic criteria, the language of publication, source of funding (industry versus other), and country.

Summary of findings and assessment of the certainty of the evidence

We present the main results of the review in the 'Summary of findings' tables. These tables present key information concerning the certainty of the evidence, the magnitude of the effects of the interventions examined, and the sum of the available data for the main outcomes (Schunemann 2020a).

The 'Summary of findings' tables also include an overall grading of the evidence related to each of the main outcomes using the GRADE (Grades of Recommendation, Assessment, Development and Evaluation) approach (GRADE 2008; GRADE 2011). The GRADE approach defines the certainty of a body of evidence as the extent to which one can be confident that an estimate of effect or association is close to the true quantity of specific interest. This will be assessed by two authors. A summary of the assessment process is in Appendix 3. The certainty of a body of evidence involves consideration of the within‐trial risk of bias (methodological quality), directness of evidence, heterogeneity, the precision of effect estimates, and the risk of publication bias (Schunemann 2020b). We plan to present the following outcomes in the 'Summary of findings' tables.

• GI function

• Graft health

• Adverse events

• Serious adverse events

• Death

Results

Description of studies

Results of the search

Our search of the Specialised Register identified a total of 26 records. After screening titles and abstracts and full‐text review, five studies (seven records) were included, 10 studies (14 records) were excluded, and we identified six ongoing studies (ChiCTR1800017180; ChiCTR1800018122; DIGEST 2021; NCT02938871; NCT04428190; UMIN000024009; 822 proposed participants). These six studies will be assessed in a future update of this review (Figure 1).

1.

Study flow diagram.

Included studies

Five studies, randomising 250 participants, met our inclusion criteria (Characteristics of included studies).

Of these, two were abstracts (Liu 2015f; Orr 2016), and three were full‐text, peer‐reviewed articles (Guida 2017; Rayes 2002; Rayes 2005). All five studies were single‐centre studies and took place in a hospital setting. Studies were undertaken in China (Liu 2015f), Germany (Rayes 2005), Italy (Guida 2017), New Zealand (Orr 2016), and Sweden (Rayes 2002). Sample sizes ranged from 30 (Orr 2016) to 66 (Rayes 2005).

All studies compared two parallel arms. One study compared a synbiotic to placebo (Guida 2017), two studies compared a probiotic to placebo (Liu 2015f; Orr 2016), and two studies compared a synbiotic to a prebiotic (Rayes 2002; Rayes 2005).

Participants were kidney or liver transplant recipients treated in the postoperative period; one study treated recipients up to 12 months post‐transplant (Guida 2017).

Excluded studies

After full‐text review, we excluded eight studies: three studies were undertaken in the wrong population (ACTRN12618001943235; C000000125; PREBIOTIC 2018), five studies compared the wrong interventions (Eguchi 2011; Grat 2017; Marks 2010; PrePro 2018; Rayes 2002a), and one study was abandoned (ISRCTN73842971) (Characteristics of excluded studies).

Ongoing studies

Six ongoing studies (822 proposed participants) were identified and will be assessed in a future update (ChiCTR1800017180; ChiCTR1800018122; DIGEST 2021; NCT02938871; NCT04428190; UMIN000024009) (Characteristics of ongoing studies).

Risk of bias in included studies

See Figure 2 for a graphical summary of the risk of bias assessment within each study.

2.

Risk of bias summary: review authors' judgements about each risk of bias item for each included study.

Most studies were characterised by an unclear risk of bias across most domains. The reason being a severe lack of information and detail to permit judgement (either abstract only or not reported).

Using funnel plots to detect publication bias was not feasible due to the lack of available data to analyse quantitatively.

Random sequence generation

Two studies were judged to have an unclear risk of bias due to a lack of information provided on randomisation methods within the abstracts, although they were stated to be randomised (Liu 2015f; Orr 2016).

Three studies were judged to be at low risk of bias for providing an adequate description of how their randomisation methods were undertaken (Guida 2017; Rayes 2002; Rayes 2005).

Allocation concealment

One study was open‐label and judged to be at high risk of bias (Rayes 2002).

Three studies were judged to have an unclear risk of bias due to a lack of information provided on how allocation was concealed for the treatment arms (Guida 2017; Liu 2015f; Orr 2016).

One study was judged to be low risk of bias; they reported only a third party knew the treatment, and "the sachets and its content looked identical in both groups" (Rayes 2005).

Performance bias

One study was open‐label and judged to be at high risk of bias (Rayes 2002).

Three studies were judged to have unclear risk of bias for either not providing any details as to how any blinding of personnel took place (Guida 2017) or not stating whether the study was blinded within the abstract (Liu 2015f; Orr 2016).

One study was judged to be at low risk of bias for reporting "the only person who knew the type of treatment received, was a study nurse who was not involved in the trial and did not treat the patients" (Rayes 2005).

Detection bias

One study was open‐label and judged to be at high risk of bias (Rayes 2002).

Four studies were judged to have unclear risk of bias for either not providing any details as to how any blinding of personnel took place (Guida 2017; Rayes 2005), or not stating whether the study was a blinded trial within the abstract (Liu 2015f; Orr 2016).

Incomplete outcome data

Two studies were judged to have unclear risk of bias as no information about withdrawals could be identified in the abstracts (Liu 2015f; Orr 2016).

Three studies were judged to be at low risk of bias. The attrition rates were 0% (Rayes 2005), 6% (Guida 2017) and 10% (Rayes 2002). Rayes 2002 stated the dropouts were not related to the study treatment.

Selective reporting

Four studies were judged to have unclear risk of bias as no information was available on trial registration or an a priori published protocol (Liu 2015f; Orr 2016; Rayes 2002; Rayes 2005). One study provided a trial registration number and was judged to be at low risk or bias (Guida 2017).

Other potential sources of bias

All five studies were judged to have unclear risk of bias as no information was provided regarding funding or reporting whether conflicts of interest needed to be disclosed.

Effects of interventions

See: Table 1; Table 2; Table 3

Outcome data were limited in the included studies. See Appendix 4 for a full outline of the extracted outcome data of all included studies.

Synbiotics versus placebo

Guida 2017 compared a synbiotic (5 × 10⁹L. plantarum; 2 x 10⁹L. casei subp. rhamnosus and 2 x 10⁹L. gasseri; 1 x 10⁹B. infantis and 1 x 10⁹B. longum; 1 x 10⁹L. acidophilus; 1 x 10⁹L. salivarus and 1 x 10⁹L. sporogenes and 5 x 10⁹S. termophilus; prebiotic inulin 2.2 g; VB Beneo Synergy 1; and 1.3 g of tapioca‐resistant starch) to placebo in kidney transplant recipients, powder 3 times/day away from meals for 30 days.

Gastrointestinal function

Synbiotics, compared to placebo, had uncertain effects on the change in microbiota composition. Guida 2017 reported the total plasma p‐cresol decreased by 40% (median (IQR): 1.79 (0.7 to 2.43) then 33% (2.3 (0.9 to 2.72) (at 15 and 30 days post‐operation, respectively) in patients receiving synbiotics and "remained stable" (3.82 (0.72 to 6.0 and 4.4 (3.0 to 6.4) at 15 and 30 days post‐operation, respectively) in patients receiving placebo (1 study, 34 participants, very low certainty evidence).

Guida 2017 observed no changes in faecal characteristics in patients receiving synbiotics compared to placebo (1 study, 34 participants, very low certainty evidence).

Adverse events

Guida 2017 reported all treatments were "well tolerated" in patients receiving synbiotics and placebo (1 study, 34 participants, very low certainty evidence).

Organ function measures

Guida 2017 reported no difference in eGFR at 30 days post‐operation in patients receiving synbiotics  (Analysis 1.1 (1 study, 34 participants): MD ‐3.80 mL/min, 95% CI ‐17.98 to 10.38; very low certainty evidence).

1.1. Analysis.

Comparison 1: Synbiotics versus placebo, Outcome 1: Organ function measures: kidney function at 30 days (eGFR)

Guida 2017 reported no difference in albumin concentration (mg/dL) at 30 days post‐operation in patients receiving synbiotics (Analysis 1.2 (1 study, 34 participants): MD ‐0.25 mg/dL, 95% CI ‐0.42 to ‐0.08; very low certainty evidence).

1.2. Analysis.

Comparison 1: Synbiotics versus placebo, Outcome 2: Organ function measures: kidney function (albumin concentration) at 30 days

Probiotics versus placebo

Liu 2015f (an abstract) compared a probiotic (unreported strains) to placebo in liver transplant recipients. Dose and duration were not reported in the abstract.

Orr 2016 (an abstract) compared a probiotic (L. rhamnosus and B.animalis 14 x 10⁹ colony forming units) to placebo in liver transplant recipients twice/day for 24 weeks.

Gastrointestinal function

Probiotics, compared to placebo, had uncertain effects on GI symptoms post‐transplant.

Liu 2015f reported more GI side effects in the placebo group within one week post‐operation (1 study, 55 participants; very low certainty evidence).

Orr 2016 reported no difference in GI side effects between the probiotics and placebo groups at 24 weeks post‐operation (1 study, 30 participants; very low certainty evidence).

Blood pressure

Orr 2016 reported no difference in BP between the probiotics and placebo groups at 24 weeks post‐operation (1 study, 30 participants; very low certainty evidence)

Organ function measures

Probiotics, compared to placebo, had uncertain effects on liver function measures.

Liu 2015f reported a difference in serum total bilirubin, serum ALT, serum albumin, and serum prealbumin between the probiotics group and the placebo group at days five and eight post‐operation (1 study, 55 participants; very low certainty evidence).

Orr 2016 reported no difference in mean change in fatty liver (controlled attenuated parameter, dB/m) between the probiotics and placebo groups at 24 weeks post‐operation (1 study, 30 participants; very low certainty evidence).

Cardiovascular disease

Orr 2016 reported no difference in lipids between the probiotics and placebo groups at 24 weeks post‐operation (1 study, 30 participants; very low certainty evidence).

Infection

Liu 2015f reported that 41.38% had a post‐transplant infection in the probiotics group and 69.23% in the placebo group within one week post‐operation (1 study, 55 participants; very low certainty evidence).

Synbiotics versus prebiotics

Rayes 2002 compared a synbiotic (L. plantarum 299 dose of 10⁹ and oat fibre to a prebiotic (instead of living lactobacilli, heat‐killed L. plantarum 299 (AB Probi) and oat fibre) in liver transplant recipients, twice/day for six weeks.

Rayes 2005 compared a synbiotic (1010 Pediacoccuspentosaceus 5‐33:3; Leuconostocmesenteroides 77:1; L.paracasei ssp. paracasei F19; and L. plantarum 2362; plus four bioactive fibres: 2.5 g of each betaglucan, inulin, pectin and resistant starch, totally 10 g/dose, or 20 g/day) to a prebiotic (four bioactive fibres via a feeding tube or orally: 2.5 g of each betaglucan, inulin, pectin and resistant starch, totally 10 g/dose, or 20 g/day) in liver transplant recipients, twice/day for 14 days post‐operation.

Gastrointestinal function

Rayes 2002 reported time to first bowel movement was 2.2 days (SD not reported) in the synbiotics group and 2.4 days (SD not reported) in the prebiotics group (1 study, 63 participants; very low certainty evidence).

Graft health

Synbiotics compared to prebiotics had an uncertain effect on the rate of acute liver rejection (Analysis 2.1 (2 studies, 129 participants): RR 0.73, 95% CI 0.43 to 1.25; I² = 0%; very low certainty evidence).

2.1. Analysis.

Comparison 2: Synbiotics versus prebiotics, Outcome 1: Graft health: acute liver rejection

Adverse events

Synbiotics, compared to prebiotics, had uncertain effects on the number of participants reporting an adverse event (Analysis 2.2 (2 studies, 129 participants): RR 0.79, 95% CI 0.40 to 1.59; I² = 20%; very low certainty evidence).

2.2. Analysis.

Comparison 2: Synbiotics versus prebiotics, Outcome 2: Adverse events: diarrhoea, abdominal distension or cramps

Serious adverse events

Synbiotics, compared to prebiotics, had uncertain effects on the number of participants reporting a serious adverse event (Analysis 2.3 (2 studies, 129 participants): RR 1.49, 95% CI 0.42 to 5.36; I² = 81%; very low certainty evidence). Appendix 4 outlines the specific non‐infectious complications such as biliary tract stenosis or fistulas, abdominal haemorrhage, and acute kidney failure.

2.3. Analysis.

Comparison 2: Synbiotics versus prebiotics, Outcome 3: Serious adverse events

Death

Synbiotics, compared to prebiotics, had uncertain effects on the number of deaths. Rayes 2002 and Rayes 2005 reported zero deaths in both treatment groups (Analysis 2.4: 2 studies, 129 participants; very low certainty evidence).

2.4. Analysis.

Comparison 2: Synbiotics versus prebiotics, Outcome 4: Death

Organ function measures

Incomplete data reported by Rayes 2002 can be found in Appendix 4.

Use of immunosuppression

Synbiotics, compared to prebiotics, had uncertain effects on the use of immunosuppression.

Rayes 2002 reported the number of patients taking immunosuppressants was: 16/32 and 13/31 taking cyclosporin, 15/31 and 19/32 taking tacrolimus, and 31/31 and 31/32 taking prednisolone in the synbiotics and prebiotics groups, respectively, at day 1 post‐operation (1 study, 63 participants; very low certainty evidence).

Rayes 2005 reported no differences in the routine use of triple regimen prednisolone, tacrolimus or cyclosporin with induction therapy with an IL‐2 antibody between the synbiotics and placebo groups at 30 days post‐operation (1 study, 66 participants; very low certainty evidence).

Infection

Synbiotics, compared to prebiotics, had uncertain effects on the total number of patients with postoperative infections up to 30 days post‐operation  (Analysis 2.5 (2 studies, 129 participants): RR 0.18, 95% CI 0.03 to 1.17; I² = 66%; very low certainty evidence).

2.5. Analysis.

Comparison 2: Synbiotics versus prebiotics, Outcome 5: Infection: post‐operative infection (up to 30 days)

Rayes 2002 reported the total number of postoperative infections was four compared to 17 in patients receiving synbiotics or prebiotics respectively. More specifically, the prebiotic group reported the highest incidence of cholangitis and enterococci as the most commonly isolated bacteria. Similarly, Rayes 2005 reported the prebiotic had the highest incidence of urinary tract infections, and E.faecalis was the most commonly isolated bacteria. Appendix 4 outlines the isolated bacteria for both studies (2 studies, 129 participants; very low certainty evidence).

Discussion

Summary of main results

Five studies (250 participants) were included in this review, with two of these being abstracts only. Study participants were adults with a kidney (one) or liver (four) transplant. Four studies were set within the postoperative setting, and one study up to 12 months post‐transplant. One study compared a synbiotic to placebo (34 participants), two studies compared a probiotic to placebo (85 participants), and two studies compared a synbiotic to a prebiotic (129 participants).

Synbiotics, compared to placebo, had uncertain effects on the change in microbiota composition (total plasma p‐cresol), faecal characteristics, adverse events, kidney function or albumin concentration.

Probiotics, compared to placebo, had uncertain effects on GI side effects, infection rates immediately post‐transplant, liver function, BP, change in fatty liver, and lipids.

Synbiotics, compared to prebiotics, had uncertain effects on graft health (acute liver rejection), the use of immunosuppression, rates of infection, GI function (time to first bowel movement), adverse events, serious adverse events, death, and organ function measures.

Overall completeness and applicability of evidence

This review highlights the severe lack of high‐quality RCTs testing the efficacy of synbiotics, prebiotics or probiotics in solid organ transplant recipients.

We have identified significant gaps in the evidence. Of the available evidence, meta‐analyses undertaken contained limited data from small studies.

Despite GI symptoms and postoperative infection being the most common reasons for high antibiotic use in this patient population, along with increased morbidity and the growing antimicrobial resistance, we found very few studies that adequately tested these as alternative treatments.

The four major issues around the completeness of the evidence were:

1. Limited sample size and insufficient power

2. Standardised dosing of synbiotics, prebiotics or probiotics

3. Standardised measuring

4. Reporting of outcomes.

The two major issues around the applicability of the evidence were:

1. Participant criteria (four studies in liver transplant, only one study in kidney transplant, and no studies in other solid organ transplants)

2. Outcome measures varied greatly by scale, unit, time points, and definitions.

Quality of the evidence

Overall, the quality of the evidence was poor. Most studies were judged to have unclear (or high) risk of bias across most domains (Figure 2).

Of the available evidence, meta‐analyses undertaken were of limited data from small studies. Data were sparse and addressed very few primary and secondary outcomes (Appendix 4).

Across all comparisons, GRADE evaluations for all outcomes were judged to be very low certainty evidence. The evidence was downgraded three stages for various reasons. Where there were data available for meta‐analysis, the evidence was downgraded twice for risk of bias and once for sparse data from small study sizes. Alternatively, the evidence was downgraded three levels to very low certainty evidence where there were no data or incomplete data reported for an outcome and could not be meta‐analysed.

Very low certainty evidence implies that we are very uncertain about results (not estimable due to lack of data or poor quality). We have no evidence to support or refute the use of synbiotics, prebiotics, or probiotics in solid organ transplant recipients, and findings should be viewed with caution.

Potential biases in the review process

This review was conducted as per the protocol following pre‐specified inclusion criteria and used comprehensive literature searches to find all relevant studies. We do not believe there are any other potential biases in this review process.

Agreements and disagreements with other studies or reviews

We are not aware of any other systematic reviews on this topic.

Authors' conclusions

Implications for practice.

Despite GI symptoms and postoperative infection being the most common reasons for high antibiotic use in this patient population, along with increased morbidity and the growing antimicrobial resistance, we found very few studies that adequately test these as alternative treatments.

There is currently no evidence to support or refute the use of synbiotics, prebiotics, or probiotics in solid organ transplant recipients, and findings should be viewed with caution. We are not certain whether synbiotics, prebiotics, or probiotics are more or less effective compared to one another, antibiotics, or standard care for improving patient outcomes in solid organ transplant recipients. Adverse events were uncommon and mild. Six studies are currently ongoing (822 proposed participants), therefore it is possible that findings may change with the inclusion of these studies in future updates.

Implications for research.

We have identified an area of significant uncertainty about the efficacy of synbiotics, prebiotics, or probiotics in solid organ transplant recipients. Future research in this field requires adequately powered RCTs comparing synbiotics, prebiotics, and probiotics separately and with a placebo measuring a standard set of core transplant outcomes (SONG 2017).

History

Protocol first published: Issue 6, 2021

Appendices

Appendix 1. Electronic search strategies

Database	Search terms
CENTRAL	synbiotic*:ti,ab,kw probiotic*:ti,ab,kw prebiotic*:ti,ab,kw (bifido* or lactobacill*):ti,ab,kw bacillus:ti,ab,kw enterococcus:ti,ab,kw escherichia:ti,ab,kw oligosaccharide*:ti,ab,kw saccharomyces:ti,ab,kw streptococcus next thermophilus:ti,ab,kw (resistant next starch):ti,ab,kw polydextrose:ti,ab,kw (dietary next (fiber or fibre)):ti,ab,kw "gum arabic":ti,ab,kw "hi‐maize":ti,ab,kw oligosaccharides:ti,ab,kw familact:ti,ab,kw "probinul neutro":ti,ab,kw inulin:ti,ab,kw {OR #1‐#19} ((heart or cardiac or kidney or renal or liver or hepatic or lung or pulmonary or pancrea*) near/2 (transplant* or graft* or allo*)):ti,ab,kw #20 and #21 in Trials
MEDLINE	Synbiotics/ Probiotics/ Prebiotics/ synbiotic*.tw. probiotic*.tw. prebiotic*.tw. or/1‐6 Bifidobacterium bifidum/ exp Lactobacillus/ Streptococcus Thermophilus/ exp Saccharomyces/ exp Bacillus/ exp Enterococcus/ Oligosaccarides/ Eschericia/ (bifido* or lactobacill*).tw. streptococcus thermophilus.tw. saccharomyces.tw. bacillus.tw. enterococcus.tw. eschericia.tw. Dietary Fiber/ Gum Arabic/ (dietary fiber or dietary fibre).tw. resistant starch.tw. polydextrose.tw. gum arabic.tw. hi‐maize.tw. oligosaccharides.tw. familact.tw. probinul neutro.tw. Inulin/ inulin.tw. or/8‐33 or/7,34 Organ Transplantation/ exp Heart Transplantation/ Kidney Transplantation/ Liver Transplantation/ exp Lung Transplantation/ Pancreas Transplantation/ ((heart or cardiac or kidney or renal or liver or hepatic or lung or pulmonary or pancrea*) adj2 (transplant* or graft* or allo*)).tw. or/36‐42 and/35,43
EMBASE	synbiotic agent/ prebiotic agent/ exp probiotic agent/ synbiotic*.tw. probiotic*.tw. prebiotic*.tw. or/1‐6 bifidobacterium bifidum/ exp Lactobacillus/ exp bacillus/ exp enterococcus/ escherichia/ oligosaccharide/ exp saccharomyces/ streptococcus thermophilus/ (bifido* or lactobacill*).tw. bacillus.tw. enterococcus.tw. escherichia.tw. oligosaccharide*.tw. saccharomyces.tw. streptococcus thermophilus.tw. dietary fiber/ gum arabic/ gum arabic.tw. (dietary adj (fiber or fibre)).tw. resistant starch.tw. polydextrose.tw. hi‐maize.tw. arabinoxylan oligosaccharides.tw. familact.tw. probinul neutro.tw. Inulin/ inulin.tw. or/8‐34 or/7,35 organ transplantation/ exp kidney transplantation/ exp heart transplantation/ exp liver transplantation/ exp lung transplantation/ exp pancreas transplantation/ ((heart or cardiac or kidney or renal or liver or hepatic or lung or pulmonary or pancrea*) adj2 (transplant* or graft* or allo*)).tw. or/37‐43 and/36,44

Appendix 2. Risk of bias assessment tool

Potential source of bias	Assessment criteria
Random sequence generation Selection bias (biased allocation to interventions) due to inadequate generation of a randomised sequence	Low risk of bias: Random number table; computer random number generator; coin tossing; shuffling cards or envelopes; throwing dice; drawing of lots; minimisation (minimisation may be implemented without a random element, and this is considered to be equivalent to being random).
	High risk of bias: Sequence generated by odd or even date of birth; date (or day) of admission; sequence generated by hospital or clinic record number; allocation by judgement of the clinician; by preference of the participant; based on the results of a laboratory test or a series of tests; by availability of the intervention.
	Unclear: Insufficient information about the sequence generation process to permit judgement.
Allocation concealment Selection bias (biased allocation to interventions) due to inadequate concealment of allocations prior to assignment	Low risk of bias: Randomisation method described that would not allow investigator/participant to know or influence intervention group before eligible participant entered in the study (e.g. central allocation, including telephone, web‐based, and pharmacy‐controlled, randomisation; sequentially numbered drug containers of identical appearance; sequentially numbered, opaque, sealed envelopes).
	High risk of bias: Using an open random allocation schedule (e.g. a list of random numbers); assignment envelopes were used without appropriate safeguards (e.g. if envelopes were unsealed or non‐opaque or not sequentially numbered); alternation or rotation; date of birth; case record number; any other explicitly unconcealed procedure.
	Unclear: Randomisation stated but no information on method used is available.
Blinding of participants and personnel Performance bias due to knowledge of the allocated interventions by participants and personnel during the study	Low risk of bias: No blinding or incomplete blinding, but the review authors judge that the outcome is not likely to be influenced by lack of blinding; blinding of participants and key study personnel ensured, and unlikely that the blinding could have been broken.
	High risk of bias: No blinding or incomplete blinding, and the outcome is likely to be influenced by lack of blinding; blinding of key study participants and personnel attempted, but likely that the blinding could have been broken, and the outcome is likely to be influenced by lack of blinding.
	Unclear: Insufficient information to permit judgement
Blinding of outcome assessment Detection bias due to knowledge of the allocated interventions by outcome assessors.	Low risk of bias: No blinding of outcome assessment, but the review authors judge that the outcome measurement is not likely to be influenced by lack of blinding; blinding of outcome assessment ensured, and unlikely that the blinding could have been broken.
	High risk of bias: No blinding of outcome assessment, and the outcome measurement is likely to be influenced by lack of blinding; blinding of outcome assessment, but likely that the blinding could have been broken, and the outcome measurement is likely to be influenced by lack of blinding.
	Unclear: Insufficient information to permit judgement
Incomplete outcome data Attrition bias due to amount, nature or handling of incomplete outcome data.	Low risk of bias: No missing outcome data; reasons for missing outcome data unlikely to be related to true outcome (for survival data, censoring unlikely to be introducing bias); missing outcome data balanced in numbers across intervention groups, with similar reasons for missing data across groups; for dichotomous outcome data, the proportion of missing outcomes compared with observed event risk not enough to have a clinically relevant impact on the intervention effect estimate; for continuous outcome data, plausible effect size (difference in means or standardised difference in means) among missing outcomes not enough to have a clinically relevant impact on observed effect size; missing data have been imputed using appropriate methods.
	High risk of bias: Reason for missing outcome data likely to be related to true outcome, with either imbalance in numbers or reasons for missing data across intervention groups; for dichotomous outcome data, the proportion of missing outcomes compared with observed event risk enough to induce clinically relevant bias in intervention effect estimate; for continuous outcome data, plausible effect size (difference in means or standardized difference in means) among missing outcomes enough to induce clinically relevant bias in observed effect size; ‘as‐treated’ analysis done with substantial departure of the intervention received from that assigned at randomisation; potentially inappropriate application of simple imputation.
	Unclear: Insufficient information to permit judgement
Selective reporting Reporting bias due to selective outcome reporting	Low risk of bias: The study protocol is available and all of the study’s pre‐specified (primary and secondary) outcomes that are of interest in the review have been reported in the pre‐specified way; the study protocol is not available but it is clear that the published reports include all expected outcomes, including those that were pre‐specified (convincing text of this nature may be uncommon).
	High risk of bias: Not all of the study’s pre‐specified primary outcomes have been reported; one or more primary outcomes is reported using measurements, analysis methods or subsets of the data (e.g. sub‐scales) that were not pre‐specified; one or more reported primary outcomes were not pre‐specified (unless clear justification for their reporting is provided, such as an unexpected adverse effect); one or more outcomes of interest in the review are reported incompletely so that they cannot be entered in a meta‐analysis; the study report fails to include results for a key outcome that would be expected to have been reported for such a study.
	Unclear: Insufficient information to permit judgement
Other bias Bias due to problems not covered elsewhere in the table	Low risk of bias: The study appears to be free of other sources of bias.
	High risk of bias: Had a potential source of bias related to the specific study design used; stopped early due to some data‐dependent process (including a formal‐stopping rule); had extreme baseline imbalance; has been claimed to have been fraudulent; had some other problem.
	Unclear: Insufficient information to assess whether an important risk of bias exists; insufficient rationale or evidence that an identified problem will introduce bias.

Appendix 3. The GRADE approach (Grades of Recommendation, Assessment, Development, and Evaluation)

The GRADE approach assesses the certainty of a body of evidence, rating it in one of four grades (GRADE 2008).

• High: we are very confident that the true effect lies close to that of the estimate of the effect

• Moderate: we are moderately confident in the effect estimate; the true effect is likely to be close the estimate of effect, but there is a possibility that it is substantially different

• Low: our confidence in the effect estimate is limited; the true effect may be substantially different from the estimate of the effect

• Very low: we have very little confidence in the effect estimate; the true effect is likely to be substantially different from the estimate of effect.

We decreased the certainty of evidence if there was (Balshem 2011):

• serious (‐1) or very serious (‐2) limitation in the study design or execution (risk of bias);

• important inconsistency of results (‐1);

• some (‐1) or major (‐2) uncertainty about the directness of evidence;

• imprecise or sparse data (‐1) or serious imprecision (‐2); or

• high probability of publication bias (‐1).

We increased the certainty of evidence if there was (GRADE 2011):

• a large magnitude of effect (direct evidence, relative risk (RR) = 2 to 5 or RR = 0.5 to 0.2 with no plausible confounders) (+1); very large with RR > 5 or RR < 0.2 and no serious problems with risk of bias or precision; more likely to rate up if effect is rapid and out of keeping with prior trajectory; usually supported by indirect evidence (+2);

• evidence of a dose‐response gradient (+1); or

• all plausible residual confounders or biases would reduce a demonstrated effect, or suggest a spurious effect when results show no effect (+1).

Appendix 4. Extracted outcome data from included studies

Outcomes	Arm 1		Arm 2
	Event or mean ± SD	Total	Event or mean ± SD	Total
Guida 2017	Synbiotic		Placebo
GI function: change in microbiotacomposition (decrease in total plasma p‐cresol from baseline) Measured by high‐performance liquid chromatography, median (IQR) Time: 15 and 30 days post‐operation	Baseline: 3.0 (1.6 to 4.5)   15 days post‐operation: 1.79 (0.7 to 2.43); decrease by 40%   30 days post‐operation: 2.3 (0.9 to 2.72); decrease by 33%   P < 0.01 versus baseline; P < 0.01 versus placebo	22	Baseline: 4.2 (2.4 to 5.8)   15 days post‐operation: 3.82 (0.72 to 6.0); remained stable   30 days post‐operation: 4.4 (3.0 to 6.4); remained stable	12
GI function: faecal characteristics (instrument not reported) Time: at 30 days post‐operation	"No changes observed"	22	"No changes observed"	12
Adverse events (not described) Time: at 30 days post‐operation	GI side effects: 0 Borborygmus: 13 Abdominal pain: "virtually absent" "Well tolerated"	22	Abdominal pain: "virtually absent" "Well tolerated"	12
Organ function measures: kidney function (eGFR mL/min) Time: at 30 days post‐operation	Baseline: 50.6 ± 17.6 30 days post‐operation: 53.5 ± 16.0   "No significant change"	22	Baseline: 58.5 ± 24.0 30 days post‐operation: 57.3 ± 22.1   "No significant change"	12
Organ function measures: kidney function (albumin mg/dL) Time: at 30 days post‐operation	Baseline: 4.53 ± 0.3 30 days post‐operation: 4.35 ± 0.3   "No significant change"	22	Baseline: 4.60 ± 0.4 30 days post‐operation: 4.35 ± 0.3   "No significant change"	12
Liu 2015f	Probiotics		Placebo
GI function: post transplant GI side effects Time: "within 1 week postop"	17.24% "Significantly higher than control group (P < 0.05)"	Not reported	42.31%	Not reported
Organ function measures: serum total bilirubin Time: postoperative day 8	"Significantly lower than control group (P < 0.05)"	Not reported	Not reported	Not reported
Organ function measures: ALT Time: postoperative day 8	"Significantly lower than control group (P < 0.05)"	Not reported	Not reported	Not reported
Organ function measures: serum albumin and prealbumin Time: postoperative day 5	"Significantly higher than control group (P < 0.05)"	Not reported	Not reported	Not reported
Organ function measures: serum albumin and prealbumin Time: postoperative day 8	"Significantly higher than control group (P < 0.05)"	Not reported	Not reported	Not reported
Infection: post‐transplant infection incidence Time: "within 1 week postop"	41.38% "Significantly higher than control group (P < 0.05)"	Not reported	69.23%	Not reported
Orr 2016	Probiotics		Placebo
BP: mean change in BP Time: at 24 weeks	"No significant difference between treatment arms"	15	"No significant difference between treatment arms"	15
Organ function measures: liver (mean change in Fibroscan CAP (dB/m), change in fatty liver) Time: at 24 weeks		15		15
CVD (mean change in lipids) Time: at 24 weeks		15		15
Rayes 2002	Synbiotics		Prebiotics
GI function: time to first bowel movement postoperative (days) Time: postoperative period	2.2 (SD not reported)	31	2.4 (SD not reported)	32
Graft health: acute liver rejection Time: postoperative period	10 (2 muromonab‐CD3 therapy)	31	15 (3 muromonab‐CD3 therapy)	32
Adverse events: number reporting abdominal side effects (distension, cramps, diarrhoea) Time: postoperative period	6	31	11	32
Serious adverse events: number reporting non‐infectious complications Time: postoperative period	Total: 16 Acute rejections: 10 (2 muromonab‐CD3 therapy) Rate of kidney insufficiencies requiring HD: 2 Relaparotomy: 4 (haemorrhage or biliary leak)	31	Total: 19 Acute rejections: 15 (3 muromonab‐CD3 therapy) Rate of kidney insufficiencies requiring HD: 4 Relaparotomy: 2 (haemorrhage or arterial stenosis)	32
Death: perioperative deaths Time: postoperative period	0	31	0	32
Organ function measures: kidney function (serum albumin) Time: postoperative period	No numerical data available	31	No numerical data available	32
Organ function measures: kidney function (SCr (mg/dL)) Time: post‐operation day 5	1.1 ± 0.09	31	Not reported	32
Organ function measures: kidney function (SCr (mg/dL)) Time: post‐operation day 10	1.3 ± 0.1	31	Not reported	32
Organ function measures: kidney function (BUN)	No numerical data available	31	No numerical data available	32
Use of immunosuppressants (postoperative immunosuppression) Time: post‐operation day 1	CSA: 16 TAC: 15 Prednisolone: 31	31	CSA: 13 TAC: 19 Prednisolone: 31	32
Infection: number with postoperative infections Time: postoperative period	4	31	11	32
Infection: total number of postoperative infections Time: postoperative period	4	31	17	32
Infection: type of postoperative infections Time: postoperative period	Cholangitis: 2 Pneumonia: 1 Sepsis: 0 UTI: 0 Wound infection: 0 Others: 1	31	Cholangitis: 8 Pneumonia: 4 Sepsis: 0 UTI: 3 Wound infection: 0 Others: 2	32
Infection: type of postoperative infections isolated bacteria Time: postoperative period	Enterococci: 1 E. coli: 0 Staphylococci: 1 Klebsiella: 0 None: 2	31	Enterococci: 8 E. coli: 1 Staphylococci: 3 Klebsiella: 1 None: 5	32
Infection: mean cumulative length of antibiotic therapy (days) Time: postoperative period	7 ± 7	31	12 ± 18	32
Other: changes in leukocyte count Time: postoperative period	"Lower in (synbiotics) group than in the other groups, but the difference was not statistically significant"	31	Not reported	32
Other: cellular immune variables: CD4/CD8 Time: postoperative period	"Course of the CD4/CD8 ratio was higher in (synbiotics) group but the difference was not statistically significant (P =  0.06)"	31	Not reported	32
Rayes 2005	Synbiotics		Prebiotics
Graft health: incidence of acute rejection	6	33	7	33
Graft health: initial non‐function of liver followed by re‐transplantation	0	33	1	33
Adverse events: number reporting diarrhoea Time: at 30 days post‐operation	Diarrhoea: 3 Abdominal cramps: 5 Abdominal distension and cramps: 0	33	Diarrhoea: 4 Abdominal cramps: 0 Abdominal distension and cramps: 3	33
Serious adverse events: number reporting non‐infectious complications Time: post‐operation	Total: 12 Biliary tract stenosis or fistulas treated endoscopically with stents: 4 Lienalis‐steal syndrome requiring intervention with angiography: 4 Abdominal haemorrhage requiring relaparotomy: 2 AKI: 2	33	Total: 4 Abdominal haemorrhage requiring relaparotomy: 2 AKI: 1 Initial non‐function of the liver followed by re‐transplantation: 1	33
Death: perioperative death Time: at 30 days post‐operation	0	33	0	33
Use of immunosuppressants: routine immunosuppression (triple regimen of prednisolone and TAC or CSA with induction therapy with an IL‐2 antibody) Time: at 30 days post‐operation	"No differences"	33	"No differences"	33
Infection: length of antibiotic therapy without prophylaxis (days) Time: at 30 days post‐operation	0.1 ± 0.1 (P < 0.05) "Significantly shorter compared to prebiotics"	33	3.8 ± 0.9	33
Infection: incidence (no. patients with an infection) Time: at 30 days post‐operation	1 (P < 0.05)	33	16	33
Infection: total types of infection (not per patient) Time: at 30 days post‐operation	Urinary tract: 1 Wound: 0 Pneumonia: 0 Cholangitis: 0   Isolated bacteria ‐ E. faecalis/faecium: 1 ‐ E. coli: 0 ‐ Enterobacter cloacae: 0 ‐ Pseudomonas aeruginosa: 0 ‐ Staphylococcus aureus: 0	‐‐	Urinary tract: 12 Wound: 1 Pneumonia: 1 Cholangitis: 2   Isolated bacteria ‐ E. faecalis/faecium: 11 ‐ E. coli: 3 ‐ Enterobacter cloacae: 2 ‐ Pseudomonas aeruginosa: 2 ‐ Staphylococcus aureus: 1	‐‐
Infection: number days with fever (< 38.5ºC) Time: during 30 days post‐operation	1	33	22	33
Footnotes: AKI: acute kidney injury; ALT: alanine aminotransferase; BP: blood pressure; BUN: blood urea nitrogen; CAP: Controlled Attenuated Parameter; CSA: cyclosporin; CVD: cardiovascular disease; eGFR: estimated glomerular filtration rate; GI: gastrointestinal; HD: haemodialysis; IL‐2: interleukin‐2; IQR: interquartile range; SCr: serum creatinine; TAC: tacrolimus; UTI: urinary tract infection

Data and analyses

Comparison 1. Synbiotics versus placebo.

Outcome or subgroup title	No. of studies	No. of participants	Statistical method	Effect size
1.1 Organ function measures: kidney function at 30 days (eGFR)	1	34	Mean Difference (IV, Random, 95% CI)	‐3.80 [‐17.98, 10.38]
1.2 Organ function measures: kidney function (albumin concentration) at 30 days	1	34	Mean Difference (IV, Random, 95% CI)	‐0.25 [‐0.42, ‐0.08]

Comparison 2. Synbiotics versus prebiotics.

Outcome or subgroup title	No. of studies	No. of participants	Statistical method	Effect size
2.1 Graft health: acute liver rejection	2	129	Risk Ratio (M‐H, Random, 95% CI)	0.73 [0.43, 1.25]
2.2 Adverse events: diarrhoea, abdominal distension or cramps	2	129	Risk Ratio (M‐H, Random, 95% CI)	0.79 [0.40, 1.59]
2.3 Serious adverse events	2	129	Risk Ratio (M‐H, Random, 95% CI)	1.49 [0.42, 5.36]
2.4 Death	2	129	Risk Ratio (M‐H, Random, 95% CI)	Not estimable
2.5 Infection: post‐operative infection (up to 30 days)	2	129	Risk Ratio (M‐H, Random, 95% CI)	0.18 [0.03, 1.17]

Characteristics of studies

Characteristics of included studies [ordered by study ID]

Guida 2017.

Study characteristics
Methods	Study design: parallel RCT Study duration and follow‐up: 30 days treatment, 30 days follow‐up
Participants	Setting: outpatient kidney transplantation clinic Country: Italy Inclusion criteria Adult kidney transplant recipients; transplant > 12 months; stable graft function; SCr < 2.5 mg/dL in the last 3 months Baseline characteristics Number: treatment group (24); control group (12) Mean age ± SD (years): treatment group (54.0 ± 8.9); control group (47.3 ± 8.5) Sex (M/F): treatment group (16/6); control group (12/0) Type of solid organ transplant: kidney Comorbidities: none reported Exclusion criteria Episodes of acute rejection or infection in the last 3 months; diarrhoea, diabetes, severe malnutrition
Interventions	Treatment group Synbiotic (Probinul Neutro, CadiGroup, Rome, Italy): contains 5 x 109L. plantarum; 2 x 109L. casei subp. rhamnosus; 2 x 109L. gasseri; 1 x 109B. infantis and 1 x 109B. longum; 1 x 109L. acidophilus; 1 x 109L. salivarus and 1 x 109L. sporogenes and 5 x 109S. termophilus; prebiotic inulin (2.2 g; VB Beneo Synergy 1); and 1.3 g of tapioca‐resistant starch 5 g powder packets dissolved in water, 3 times/day, away from meals, for 30 days Control group Placebo: tapioca‐resistant starch powder 5 g powder packets dissolved in water, 3 times/day, away from meals, for 30 days Co‐interventions or additional treatments Patients were already taking the Mediterranean pattern diet in accordance with nutritional dietary guidelines for kidney transplanted patients. Protein intake was restricted to 0.8 g/kg of ideal body weight/day Follow‐up details At the end of 30 days of treatment
Outcomes	Outcomes reported at 15 and 30 days Decrease in total plasma p‐cresol measured by high‐performance liquid chromatography Kidney function: eGFR Glycaemia Plasma lipids Albumin concentration Adverse events Change in stool characteristics
Notes	Trial registration: NCT02179229 A priori protocol publication: not reported Conflicts of interest: not reported Funding declared: not reported Publication type: full‐text article
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	Quote: patients were "were enrolled in this single‐center, parallel‐group, double‐blinded, randomized (2:1 synbiotic to placebo) study...Using a computer‐generated random binary list, they were allocated to one of 2 arms"
Allocation concealment (selection bias)	Unclear risk	Comment: no information provided in full‐text article about concealment methods
Blinding of participants and personnel (performance bias) All outcomes	Unclear risk	Quote: patients "were enrolled in this ... double‐blinded ... study" Comment: insufficient information provided in full‐text article about how blinding methods were applied
Blinding of outcome assessment (detection bias) All outcomes	Unclear risk	Comment: no information provided in full‐text article about outcome assessors being blinded
Incomplete outcome data (attrition bias) All outcomes	Low risk	Quote: "two patients in the synbiotic group dropped out for reasons unrelated to treatment" Comment: 6% attrition with reasons provided, not linked to study medication
Selective reporting (reporting bias)	Low risk	A priori protocol publication: not reported in full‐text article Comment: planned outcomes were measured and reported
Other bias	Unclear risk	Conflicts of interest: not reported in full‐text article Funding declared: not reported in full‐text article

Liu 2015f.

Study characteristics
Methods	Study design: open‐label, parallel RCT Study duration and follow‐up: not reported
Participants	Setting: single centre Country: China Inclusion criteria Orthotopic liver transplant recipients Baseline characteristics Number: 55 (number per group not reported) Mean age ± SD (years): not reported Sex (M/F): not reported Type of solid organ transplant: liver Comorbidities: not reported Exclusion criteria Not reported
Interventions	Treatment group Probiotics (strains not reported) Dose, frequency, and duration not reported Control group Placebo Dose, frequency, and duration not reported Co‐interventions or additional treatments Immunosuppressants Follow‐up details Not reported
Outcomes	Outcomes reported at days 2, 5, 8 postoperatively Serum total bilirubin Serum ALT Serum albumin and prealbumin Post‐transplant infection incidence Post‐transplant GI side effects
Notes	Trial registration: not reported A priori protocol publication: not reported Conflicts of interest: not reported Funding declared: not reported Publication type: abstract only
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	Quote: "patients ... were randomly divided into control group and Probiotics group" Comment: insufficient information provided within the abstract about randomisation methods
Allocation concealment (selection bias)	Unclear risk	Comment: no information provided within abstract about concealment methods
Blinding of participants and personnel (performance bias) All outcomes	Unclear risk	Comment: no information provided within abstract about blinding participants
Blinding of outcome assessment (detection bias) All outcomes	Unclear risk	Comment: no information provided within abstract about outcome assessors being blinded
Incomplete outcome data (attrition bias) All outcomes	Unclear risk	Comment: withdrawals and completers not reported within abstract
Selective reporting (reporting bias)	Unclear risk	Comment: unable to assess selective reporting from abstract A priori protocol publication: not reported in abstract
Other bias	Unclear risk	Conflicts of interest: not reported in abstract Funding declared: not reported in abstract

Orr 2016.

Study characteristics
Methods	Study design: parallel, open‐label RCT Study duration and follow‐up: 24 weeks treatment, follow‐up at 24 weeks; study dates not reported
Participants	Setting: single centre Country: New Zealand Inclusion criteria Patients with post liver transplant metabolic syndrome Baseline characteristics Number: treatment group (15); control group (15) Mean age (range): 57 years (42 to 76) Sex (M/F): not reported Type of solid organ transplant: liver Comorbidities: post liver transplant metabolic syndrome Exclusion criteria Not reported
Interventions	Treatment group Probiotic supplementation with L. rhamnosus and B.animalis 14 x 109 CFU/day, twice/day for 24 weeks Control group Placebo capsules Twice/day for 24 weeks Co‐interventions or additional treatments Pre randomisation: commenced on a 4 week VLCD with dietary advice and provision of Optifast meal replacements (600 kcal/day) to initiate weight loss Interventions above started at week 5 Follow‐up details At 24 weeks of treatment
Outcomes	Outcomes reported at 24 weeks Change in liver enzymes (including lipids, glycaemia, BP) Change in Fibroscan CAP (change in fatty liver)
Notes	Trial registration: not reported A priori protocol publication: not reported Conflicts of interest: not reported Funding declared: not reported Publication type: abstract only
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	Quote: "patients were then randomised 1‐1 to either twice daily probiotic capsules or twice daily placebo capsules" Comment: insufficient information provided within abstract about randomisation methods
Allocation concealment (selection bias)	Unclear risk	Comment: no information provided within abstract about concealment methods
Blinding of participants and personnel (performance bias) All outcomes	Unclear risk	Comment: no information provided within abstract about blinding participants
Blinding of outcome assessment (detection bias) All outcomes	Unclear risk	Comment: no information provided within abstract about outcome assessors being blinded
Incomplete outcome data (attrition bias) All outcomes	Unclear risk	Comment: withdrawals and completers not reported within abstract
Selective reporting (reporting bias)	Unclear risk	Comment: unable to assess selective reporting from abstract A priori protocol publication: not reported in abstract
Other bias	Unclear risk	Conflicts of interest: not reported in abstract Funding declared: not reported in abstract

Rayes 2002.

Study characteristics
Methods	Study design: parallel, open‐label RCT Study duration and follow‐up: 14 days treatment, 6 weeks follow‐up; from October 1997 to October 1999
Participants	Setting: single centre Country: Sweden Inclusion criteria Adults undergoing orthotopic liver transplantation with side‐to‐side anastomosis of the bile duct Baseline characteristics Number*: treatment group (31); control group (32) Mean age ± SD (years): treatment group (50 ± 2); control group (50 ± 2) Sex (M/F): treatment group (15/16); control group (15/17) Type of solid organ transplant: orthotopic liver transplantation Comorbidities: not reported Exclusion criteria Adults with severe kidney insufficiency (CrCl < 50 mL/min) Intestinal obstruction (ileus) Cerebral disorders with danger of aspiration Roux‐en‐Y reconstruction of the bile duct *Three groups were studied however, we did not analyse the selective bowel decontamination group in this review
Interventions	Treatment group Synbiotics: 15g/L fibre divided into 0.6 g/L soluble and 14.4 g/L nonsoluble fibres First 12 days: L. plantarum 299 (AB Probi, Lund, Sweden) in a dose of 109 and oat fibre were added twice/day via the feeding tube Enteral nutrition: 1000 kcal/L, 40 g protein/L, 123 g carbohydrate/L, and 29 g lipid/L Oral intake started with clear liquids on postoperative day 1 and increased thereafter slowly for 6 weeks postoperatively Control group Placebo (prebiotics alone): instead of living lactobacilli, heat‐killed L. plantarum 299 (AB Probi) and oat fibre were supplied twice daily Enteral nutrition: 1000 kcal/L, 40 g protein/L, 123 g carbohydrate/L, and 29 g lipid/L Oral intake started with clear liquids on postoperative day 1 and increased thereafter slowly for 6 weeks postoperatively Co‐interventions or additional treatments Postoperative immunosuppression: CSA or TAC, together with prednisolone Some patients also received an induction therapy with an IL‐2‐receptor antibody Rapamycin or MMF added if clinically indicated All patients received IV antibiotic prophylaxis: ceftriaxone (2 g twice/day) and metronidazole (500 mg twice/day), 30 min prior to surgery until 2 days post‐operation Follow‐up details 6 weeks postoperatively
Outcomes	Outcomes reported at 6 weeks post‐operation Intra and postoperative blood transfusions (units): RBC, fresh frozen plasma Postoperative immunosuppression Serum albumin SCr BUN Changes in leukocyte count Cellular immune variables: CD4/CD8 Postoperative infections and other complications: rate of postoperative infections; type of infections; mean time to onset of postoperative infection Mean cumulative length of antibiotic therapy Noninfectious complications: acute rejections; rate of kidney insufficiencies requiring HD; relaparotomy Perioperative deaths First bowel movement postoperative Abdominal side effects: distension, cramps, diarrhoea
Notes	Trial registration: not reported A priori protocol publication: not reported Conflicts of interest: not reported Funding declared: not reported Publication type: full text
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	Quote: "all patients were stratified using the classification of the American Society of Anaesthesiologists (ASA). After stratification, patients were randomized by sealed envelope into one of the following three study groups"
Allocation concealment (selection bias)	High risk	Comment: open‐label study
Blinding of participants and personnel (performance bias) All outcomes	High risk	Comment: open‐label study
Blinding of outcome assessment (detection bias) All outcomes	High risk	Comment: open‐label study
Incomplete outcome data (attrition bias) All outcomes	Low risk	Comment: attrition = 10% (reasons for non‐completers provided and not related to study intervention: surgical complications rendering enteral treatment difficult)
Selective reporting (reporting bias)	Unclear risk	Comment: unable to assess selective reporting A priori protocol publication: not reported and not located
Other bias	Unclear risk	Conflicts of interest: not reported Funding declared: not reported

Rayes 2005.

Study characteristics
Methods	Study design: parallel RCT Study duration and follow‐up: 14 days treatment, 30 days follow‐up (study dates not reported)
Participants	Setting: single centre Country: Germany Inclusion criteria Adults scheduled for liver transplantation Baseline characteristics Number: treatment group (33); control group (33) Mean age ± SD (years): treatment group (53 ± 2); control group (50 ± 2) Sex (M/F): treatment group (22/11); control group (16/17) Type of solid organ transplant: liver Comorbidities: not reported Exclusion criteria Decompensated kidney insufficiencies (CrCl < 50 mL/min) Cerebral disorders with danger of aspiration Patients with roux and Y‐anastomosis
Interventions	Treatment group Synbiotic (Synbiotic2000 Medipharm) via feeding tube or orally 1010 Pediacoccuspentosaceus 5‐33:3, Leuconostocmesenteroides 77:1, L.paracasei ssp. paracasei F19, and L. plantarum 2362 Plus four bioactive fibres: 2.5 g of each betaglucan, inulin, pectin and resistant starch, totally 10 g/dose, or 20 g/day Twice/day for 14 days post‐operation Control group Prebiotics: four bioactive fibres via a feeding tube or orally: 2.5 g of each betaglucan, inulin, pectin and resistant starch, totally 10 g/dose, or 20 g/day Twice/day for 14 days post‐operation Co‐interventions or additional treatments Enteral nutrition with a low‐fibre formula IV prophylaxis: cefuroxime (1.5 g) and metronidazole (500 mg) twice/day for 36 hours starting 30 min before operation Follow‐up details 30 days post‐operation
Outcomes	Outcomes reported during 30 day postoperative period Post‐operative bacterial infection during the first 30 post‐operative days: incidence, type of infections, and type of isolated bacteria Side effects of enteral nutrition Duration of antibiotic therapy: number of days on which the patients received antibiotic therapy Non‐infectious complications: biliary fistulas, anastomotic leaks, intraabdominal haemorrhage, vascular complications, rejections and impaired kidney function requiring HD Relaparotomies Laboratory values post‐operative days 1, 4 and 8: including haematology, clinical chemistry with bilirubin, BUN, CRP, IgA, transferrin and prealbumin Bacterial infection (fever > 38°C, elevation of CRP, specific clinical symptoms of infection as shown below and a positive bacterial culture: UTI; wound infections; pneumonia; cholangitis
Notes	Trial registration: not reported A priori protocol publication: not reported Conflicts of interest: not reported Funding declared: not reported Publication type: full text
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	Quote: "all patients were stratified using the classification of the American Society of Anaesthesiologists (ASA). Then patients were randomized by sealed envelope into one of the two study groups"
Allocation concealment (selection bias)	Low risk	Quote: "the sachets and its content looked identical in both groups"
Blinding of participants and personnel (performance bias) All outcomes	Low risk	Quote: "the only person who knew the type of treatment received, was a study nurse who was not involved in the trial and did not treat the patients"
Blinding of outcome assessment (detection bias) All outcomes	Unclear risk	Comment: insufficient information provided
Incomplete outcome data (attrition bias) All outcomes	Low risk	Comment: attrition = 0%
Selective reporting (reporting bias)	Unclear risk	Comment: unable to assess selective reporting A priori protocol publication: not reported and not located
Other bias	Unclear risk	Conflicts of interest: not reported in text Funding declared: not reported in text

ALT: alanine aminotransferase; BUN: blood urea nitrogen; CAP: controlled attenuated parameter; CFU: colony forming units; CrCl: creatinine clearance; CRP: C‐reactive protein; CSA: cyclosporin; eGFR: estimated glomerular filtration rate; HD: haemodialysis; IgA: immunoglobulin A; IL‐2: interleukin‐2; IV: intravenous; M/F: male/female; MMF: mycophenolate mofetil; RBC: red blood cells; RCT: randomised controlled trial; SCr: serum creatinine; SD: standard deviation; TAC: tacrolimus; UTI: urinary tract infection; VLCD: very low calorie diet

Characteristics of excluded studies [ordered by study ID]

Study	Reason for exclusion
ACTRN12618001943235	Wrong study population: perioperative, not post‐transplant
C000000125	Wrong study population: perioperative, not post‐transplant
Eguchi 2011	Wrong intervention: syn‐, pre‐ or probiotics taken prior to transplantation
Grat 2017	Wrong intervention: syn‐, pre‐ or probiotics taken prior to transplantation
ISRCTN73842971	Study abandoned
Marks 2010	Wrong intervention: syn‐, pre‐ or probiotics taken prior to transplantation
PREBIOTIC 2018	Wrong population: perioperative, not post‐transplant
PrePro 2018	Wrong intervention: syn‐, pre‐ or probiotics taken prior to transplantation
Rayes 2002a	Wrong intervention: syn‐, pre‐ or probiotics intervention was not given to the treatment arm containing liver transplant patients

Characteristics of ongoing studies [ordered by study ID]

ChiCTR1800017180.

Study name	Study of clinical effects in liver transplantation with probiotics‐optimized early enteral nutrition of ERAS
Methods	Study design: parallel RCT Study duration and follow‐up: not reported
Participants	Setting: Hospital Country: China Inclusion criteria Aged 18 to 65 years Primary liver transplantation surgery Informed consent Exclusion criteria Combined organ transplantation Intestinal dysfunction
Interventions	Treatment group Prebiotics‐optimized early enteral nutrition Target sample size: 103 Control group Total parenteral nutrition support Target sample size: 103
Outcomes	Incidence of postoperative infection Length of hospital stay Incidence of complications
Starting date	Registration date: 17/07/2018
Contact information	Yanjie Hu Email: 13281116122@163.com T: +86 13281116122 Institution: West China Hospital, Sichuan University Address: 37 Guoxue Lane, Wuhou District, Chengdu, Sichuan, China
Notes	Trial registration: ChiCTR1800017180 URL: https://www.chictr.org.cn/showprojen.aspx?proj=28983 Funding declared: West China Hospital, Sichuan University Ethics approval: not clear

ChiCTR1800018122.

Study name	Probiotics decrease the occurrence of metabolic disorders under the guidance of FMO3 genotype after liver transplantation
Methods	Study design: parallel RCT Study duration and follow‐up: not reported
Participants	Setting: multicentre Country: China Inclusion criteria Patients underwent orthotopic liver transplantation Aged ≥ 18 years Known FMO3 rs2266782 genotype Be able to give informed consent Han nationality Exclusion criteria Living donors
Interventions	Treatment group Probiotics Control group No treatment Total sample size: 400
Outcomes	Blood glucose BP Lipids BMI
Starting date	Registration date: 31/08/2018 Recruitment dates: from 2018‐10‐01 To 2021‐04‐01
Contact information	Junwei Fan Email: drjunweifan@163.com T: +86 13917865931 Institution: Shanghai General Hospital Address: 85 Wunjin Road, Hongkou Distinct, Shanghai, China
Notes	Trial registration: ChiCTR1800018122 URL: https://www.chictr.org.cn/showprojen.aspx?proj=30371 Funding declared: Shanghai General Hospital

DIGEST 2021.

Study name	Protocol for a pilot single‐centre, parallel‐arm, randomised controlled trial of dietary inulin to improve gut health in solid organ transplantation: the DIGEST study
Methods	Study design: parallel RCT; randomised 4 weeks post‐transplant Study duration and follow‐up: 4 weeks of treatment; 12 weeks follow‐up
Participants	Setting: single centre Country: Australia Inclusion criteria: recipients of a kidney transplant from a living or deceased donor; aged ≥18 years who are able to give informed consent, and a willingness to participate and comply with the study requirements.; receive a kidney from an ABO blood group incompatible donor, or as part of the Paired Kidney Exchange Programme Exclusion criteria: diagnosed with significant GI diseases; receive antithymocyte globulin as induction or treatment for rejection; acute rejection in the first 4 weeks post‐transplant; delayed graft function requiring dialysis persisting beyond week 2 post‐transplant; presence of GI tract output stoma; current enrolment in another intervention or investigational drug trial; recipients of multiorgan transplants; known food intolerance, allergy or sensitivity to inulin or dietary fibre
Interventions	Intervention group Inulin: 10 g each morning for the first 7 days, increasing to 10 g morning and night for the remaining 21 days of the intervention period Inulin will be provided in powdered form and contained within individual 10 g sachets. The contents of each sachet will be self‐administered by the study participant by dissolving in approximately 200 mL of water prior to consuming Control group Consume one glass of water (approximately 200 mL) each morning for the first 7 days, increasing to morning and night for the following 21 days Co‐interventions Standard post‐transplant care as per the local practice guidelines Target sample size: 40
Outcomes	Weight BP Current medications Gastrointestinal symptoms rating scale Haematological and biochemical parameters 4‐day food diary 75 g oral glucose tolerance test Protocol biopsy Adverse events
Starting date	Not yet recruiting
Contact information	Prof Steven Chadban Email: Steve.Chadban@health.nsw.gov.au Kidney Node, Level 2 Charles Perkins Centre, Building D17 Johns Hopkins Drive (off Missenden Road) The University of Sydney NSW 2006 Australia
Notes	Trial registration: ACTRN12620000623998

NCT02938871.

Study name	Effect of synbiotic on postoperative complications after liver transplantation ‐ a randomized double‐blind clinical trial
Methods	Study design: parallel RCT Study duration and follow‐up: 15 days of treatment
Participants	Setting: Hospital Country: Brazil Inclusion criteria Adults ≥ 18 years Males and females Undergoing liver transplantation Exclusion criteria Health volunteers
Interventions	Treatment group Synbiotic dietary supplement: the patients of this group will receive 6 g of synbiotic composition, to be administered via a feeding tube or orally, twice/day for 15 consecutive days Control group Placebo control: the patients of this group will receive 6 g of maltodextrin, to be administered via a feeding tube or orally, twice/day for 15 consecutive days Target sample size: 76
Outcomes	Length of postoperative hospital stay: up to 12 weeks, length of hospital stay will be counted in days Duration of antibiotic therapy: up to 30 days, the duration of antibiotic therapy will be counted in days Death: up to 30 days, it will be considered death the events occurring up to 30 days after surgery Nutritional status of patients undergoing liver transplantation using the questionnaire of subjective global assessment and the global nutritional assessment proposed by Royal Free Hospital: until one month before surgery and 10 days after surgery
Starting date	Recruiting: 19/10/2016 Estimated completion: January 2018
Contact information	Dr Cleber Kruel Institution: Hospital de Clínicas de Porto Alegre
Notes	Trial registration: NCT02938871 URL: https://clinicaltrials.gov/ct2/show/NCT02938871 Funding declared: Hospital de Clinicas de Porto Alegre

NCT04428190.

Study name	Prebiotic therapy to improve outcomes of renal transplant
Methods	Study design: parallel RCT Study duration and follow‐up: 3 months treatment
Participants	Setting: multicentre Country: UK Inclusion criteria Aged ≥ 18 years Receiving a kidney transplant Exclusion criteria < 18 years Inability to give consent Usage of probiotics or other prebiotics Have had carcinomas during the last 5 years Bowel surgery Crohn's disease and other conditions
Interventions	Treatment group Synbiotic dietary supplement: HMO 10 g sachet, self‐administered for 3 months 2'‐O‐fucosyllactose and lacto‐N‐neotetraose, novel HMO sugars have been shown to stimulate the production of short chain fatty acids, especially propionate. Propionate has been shown to be important in attenuating hypertrophy, fibrosis, vascular dysfunction and hypertension and extremely important for the gut kidney axis Control group Placebo: 10 g sachet, self‐administered for 3 months Placebo sachets are identical to the HMO sachets in colour, taste, smell, size and shape Target sample size: 60
Outcomes	Primary outcomes SF‐36: 24 weeks and will measure participant satisfaction using a scale from 1 ‐ 5, 1 being the best outcome, and 5 being the worst outcome. Adverse events: recorded through case report forms and reported to the principal investigator. Side effects will be assessed using standardized case report forms at each visit. Participants are encouraged to contact the coordinator to report any concerns; 24 weeks Secondary outcomes Microbiome changes from baseline to end of treatment (12 weeks): changes in the entire bacterial community from baseline to end of study will be assessed in the lab from faecal and urine samples collected by the participant. The microbes may vary by participant and the study will be looking at which ones present themselves in each case. Units of measure via culture are CFU/g Microbiome changes post‐intervention (12 weeks): changes in the entire bacterial community after study intervention will be assessed in the lab from faecal and urine samples collected by the participant. The microbes may vary by participant and this outcome measure will be looking at which ones present themselves in each case Number who experience kidney rejection (24 weeks): kidney rejection will be recorded in the adverse event form for the study Immunosuppression suppressive drug dose: will be assessed by the clinic on post‐operative days 1, 7, 30, 60, 90, 120, 150 and 180 Infectious complications (post‐operative days 30, 60, 90, 120, 150 and 180): CMV will be tested by the clinic, typically reported in IU/mL SCr (24 weeks): will be used to determine graft function, and is reported in μmol/L Cystatin‐C levels (24 weeks): will be used to determine graft function, and is reported in mg/L eGFR (24 weeks): will be used to determine graft function, and is reported in mL/min/1.73 m² Urine output (24 weeks): will be used to determine graft function, and is reported in mL/day UPCR (24 weeks): will be used to determine graft function, and is reported in g/L Dialysis episodes (24 weeks): will be used to determine graft function, and will be measured by the amount of times a participant required dialysis Renal microperfusion using Doppler ultrasound (24 weeks): will be used to determine graft function by providing an assessment of vascular changes Kidney Injury Molecule‐1 (24 weeks): will be used to determine graft function, and is reported in ng/mL NGAL (24 weeks): will be used to determine graft function, and is reported in ng/mL Immunosuppression drug serum levels (MMF and TAC (post‐operative days 1, 7, 30, 60, 90, 120, 150 and 180): will be assessed by the clinic, typically reported in mg/mL Serial viral serologies (post‐operative days 30, 60, 90, 120, 150 and 180): polyomavirus will be tested by the clinic post‐op, typically reported in IU/mL
Starting date	Recruitment status: not yet recruiting as of 18/02/2021 Estimated start date: 01/07/2021 Estimated completion date: 15/03/2022
Contact information	Alp Sener, MD, London Health Sciences Centre Mounirah May Email: mounirah.may@lhsc.on.ca Jeremy P Burton, PhD Email: Jeremy.Burton@LawsonResearch.com
Notes	Trial registration: NCT04428190 URL: https://clinicaltrials.gov/ct2/show/NCT04428190 Funding declared: Lawson Health Research Institute

UMIN000024009.

Study name	Randomised control study evaluating the efficacy and the intestinal microbiota by perioperative administration of probiotics for liver transplant recipients
Methods	Study design: parallel, open‐label RCT Study duration and follow‐up: 2 months treatment
Participants	Setting: single centre Country: Japan Inclusion criteria Liver transplant recipients Aged ≥ 20 years Eligible for enteral feeding Written informed consent Exclusion criteria History of allergy to the drug Those attending doctors regarded as inappropriate as candidates
Interventions	Treatment group Administration of probiotics for 2 months or until discharge, whichever longer Clostridium butyricum MIYAIRI 3 g/day Control group No treatment Target sample size: 40
Outcomes	Surgical complications including infection, rejection, prognosis Laboratory test results including blood examination and microbiological examination Vital signs Prognosis
Starting date	Recruitment completed: 17/09/2019
Contact information	Satoshi Ichiyama Email: ict@kuhp.kyoto‐u.ac.jp T: 075‐751‐3111 Institution: Kyoto University Hospital Address: Department of Clinical Laboratory, Shogoin Kawaharacho 54, Sakyo, Kyoto, 6068507
Notes	Trial registration: UMIN000024009 URL: https://upload.umin.ac.jp/cgi‐open‐bin/ctr_e/ctr_view.cgi?recptno=R000027646 Funding declared: Kyoto University

BMI: body mass index; BP: blood pressure; CFU: colony forming units; CMV: cytomegalovirus; eGFR: estimated glomerular filtration rate; FMO3: flavin‐containing monooxygenase; GI: gastrointestinal; HMO: human milk oligosaccharide; MMF: mycophenolate mofetil; NGAL: neutrophil gelatinase‐associated lipocalin; RCT: randomised controlled trial; SCr: serum creatinine; SF‐36: Short Form Health Survey; TAC: tacrolimus; UPCR: urine protein/creatinine ratio

Differences between protocol and review

No differences.

Contributions of authors

1. Draft the protocol: TC, NSR, JC, CH, MH, DJ, ATP, AT, GW

2. Study selection: TC, NSR

3. Extract data from studies: TC, NSR

4. Enter data into RevMan: TC, NSR

5. Carry out the analysis: TC, NSR, ATP

6. Interpret the analysis: TC, NSR, ATP

7. Draft the final review: TC, NSR, JC, CH, MH, DJ, ATP, AT, GW

8. Disagreement resolution: MH

9. Update the review: TC, GW

Sources of support

Internal sources

• No sources of support provided

External sources

• BEAT‐CKD Funding Grant 1092957, Australia

  TC and RK are employed under funding from this grant.

Declarations of interest

• TC: none known

• NSR: none known

• JC: none known

• CH: has received fees paid to her institution from Janssen and GlaxoSmithKline; Advisory Board fees paid to her from Otsuka; Research Grants to her institution from Otsuka, Shire, Fresenius, and Baxter; none of these are related to the current study. In addition, she has received grants paid to her institution from the Polycystic Kidney Disease Foundation of Australia for work that is not related to the current study

• MH: none known

• DJ: has previously received consultancy fees, research grants, speaker's honoraria and travel sponsorships from Baxter Healthcare and Fresenius Medical Care. He has also received consultancy fees from AstraZeneca and Awak, speaker's honoraria from Ono, and travel sponsorships from Amgen. He is a current recipient of a National Health and Research Council Practitioner Fellowship

• ATP: none known

• AT: none known

• GW: none known

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