N‐acetylcysteine as an adjuvant therapy for Helicobacter pylori eradication

Abstract

This is the protocol for a review and there is no abstract. The objectives are as follows:

To assess the efficacy and safety of N‐acetylcystein (NAC) as an adjuvant therapy to antibiotics for Helicobacter pylori (H pylori) eradication.

Background

Description of the condition

Although since 1875, several scientists have observed that gastric tissue specimens and gastric aspirates had bacteria (Blaser 2005), it was only in 1982 that two Australian physicians isolated a gram‐negative microaerophilic spiral bacterium from gastric specimens which appeared initially to be of the Campylobacter genus (Marshall 1984), and that were supposed to be associated with gastritis. Some years later, observations of the bacterial structure demonstrated that they did not fulfil some characteristics of the Campylobacter genus. A new species was created and entitled Helicobacter and later the micro‐organism was named Helicobacter pylori (H pylori).

H pylori is one of the most successful pathogens to establish and cause infection in human beings, after only Streptococcus mutans (S mutans) (Cammarota 2012). Colonisation occurs in 50% of the adult population (Hunt 2011), with a wide variation in prevalence according to the region studied. Prevalence may be as high as 83% in Latin America countries and as low as 17% in North America (Calvet 2013). Approximately 20% of infected people will manifest disease (Venerito 2013). High‐risk patients include those who live in developing countries with poor sanitary conditions, since the mechanism of transmission seems to be oral‐oral or faecal‐oral mostly during infancy (Dunn 1997). Strains of bacteria are present in faeces, saliva, gastric mucosa, and dental plaque, reinforcing the hypothesis of these routes of transmission (Momtaz 2012). A positive result in the urea breath test, serology, stool antigen test, endoscopic biopsies with rapid urease reaction, histology or culture, confirms the diagnosis of H pylori infection.

The micro‐organism acts by disrupting the mucosal layer of the stomach, adhering to epithelial cells and leading to chronic inflammation of gastric mucosa. Persistent Inflammation leads to chronic gastritis, atrophy, intestinal metaplasia, dysplasia, and neoplasm (Correa 1992). Important virulence factors of H pylori contribute to successful colonisation and infection. These include:

• urease synthesis ‐ to inactivate toxicity by gastric urea and to resist in acidic milieu;

• flagella, lipases, and proteases ‐ to penetrate the intimacy of mucus;

• adhesins ‐ to attach to epithelial cells and allow interaction;

• effector toxins ‐ including cytotoxin‐associated gene A (CagA), vacuolating cytotoxin gene A (VacA), and others, which induce changes in epithelium cytoskeleton and secretion of interleukin 8 (IL‐8) (Kao 2016).

Current data show that H pylori infection is associated with a range of gastric diseases (most as a result of chronic inflammation), including atrophic gastritis, mucosal‐associated lymphoid tissue (MALT) lymphoma, peptic ulcer disease, gastric cancer, and functional dyspepsia (Kuipers 1997; Malfertheiner 2009; Zhao 2014). Some non‐gastric conditions are also associated with H pylori infection, such as idiopathic thrombocytopenic purpura (Stasi 2009), and idiopathic iron deficiency anaemia (Chaabane 2011).

See Appendix 1 for a glossary of terms.

Description of the intervention

Several regimens of antibiotic treatment are available for H pylori eradication, most of them associated with a proton pump inhibitor (PPI) to enhance bioavailability and chemical properties of antibiotics and raise cure rates. Since the 1990s PPI‐clarithromycin triple therapy has become the first‐line treatment of H pylori infection. This regimen consists of a PPI plus clarithromycin plus amoxicillin or metronidazole. Only one decade later, the efficacy of such therapy declined with clarithromycin resistance emerging as the most important cause. Other explanations for the decrease in eradication rates of PPI‐clarithromycin triple therapy are compliance, type of strains, high gastric acidity and high bacterial load. Eradication rates dropped from about 80% in the early 1990s to less than 70% a decade later (Graham 2010).

In 2012, the European Helicobacter Study Group (EHSG) published the Maastricht IV/Florence Consensus Report (EHSG 2012), proposing an approach based on local clarithromycin resistance patterns, assuming a threshold of 15% to 20% to separate regions with high and low clarithromycin resistance. Other antibiotic regimens using combinations of metronidazole, fluoroquinolones, tetracycline, and bismuth exhibit the same concerns about increasing resistance rates. If eradication was unsuccessful after an initial therapy (so‐called 'first‐line therapy'), patients would need a second treatment with a different regimen. If this second‐line treatment failed, the third regimen would need to be guided by culture and antibiogram (Malfertheiner 2012).

New approaches are being tested to enhance H pylori eradication rates, such as probiotics, statins, curcumin, and N‐acetylcysteine (NAC).

NAC is a component of amino acid L‐cysteine, available in intravenous or oral preparations. After oral ingestion, it is almost entirely absorbed and metabolised by the small intestine and liver. Only a small concentration of intact NAC reaches the plasma and tissues (De Caro 1989). Peak plasma levels are observed after less than one hour; half‐life is about two hours and it is not detectable in plasma after 10 to 12 hours (Borgstrom 1986). NAC may be administered orally or intravenously, and it seems to have a good safety profile at dosages of 1200 mg twice daily or lower. Severe adverse effects are rare and include gastrointestinal, cutaneous, and allergic effects (Kelly 1998; Millea 2009).

NAC metabolites stimulate glutathione synthesis, promoting detoxification and acting mainly as free oxygen radical scavengers. NAC promotes the cleavage of disulfide bonds of mucus glycoproteins, reducing viscosity and thickness of mucus, including the gastric mucus layer. Due to these properties, NAC has been used in several clinical situations, such as chronic obstructive pulmonary disease, influenza, idiopathic pulmonary fibrosis, polycystic ovary syndrome, prevention of contrast‐induced nephropathy, acetaminophen overdose, cancer, heart disease, and heavy metal toxicity (Kelly 1998; Millea 2009; Sherwood 2002).

NAC was first proposed as an adjuvant therapy for H pylori in the Zala 1994 trial that demonstrated improved eradication rates in patients randomised to receive antibiotics and NAC, compared with a control group that received only antibiotics.

Following on from the Zala 1994 trial, other trials demonstrated conflicting results. Some of them reported better eradication rates when NAC was associated with antibiotics (Cammarota 2010; Hamidian 2015; Gurbuz 2005), and others reported no beneficial effect on eradication rates (Emami 2014; Hansen 1994; Karbasi 2013; Yoon 2015).

How the intervention might work

Biofilms are complex biological systems produced by various species of bacteria. H pylori produce an extracellular polymeric matrix (polysaccharides, DNA, proteins and lipids) with water channels as a strategy to overcome environmental stress and protect itself. Colonies of H pylori can live embedded in biofilms in two primary forms: spiral or coccoid. Spiral forms are cultivable and virulent, while coccoid forms are viable but non‐cultivable, latent, and more resistant to adverse environmental conditions and antibiotics (Cammarota 2012).

The biofilm complex allows micro‐organisms to adhere to surfaces and proliferate under adverse conditions and also to cause refractory clinical infections (Hall‐Stoodley 2009). Current data show that biofilms are responsible for about 80% of chronic infections. Bacteria in biofilms are 1000 times more resistant to antibiotics and human defences than free‐living ones. Biofilms can worsen resistance rates to antimicrobials, retarding antibiotic diffusion, allowing expression of gene resistance, having chemical properties that impair the effect of some antibiotics , producing beta‐lactamases, decreasing the bacterial growth ratio (target of some antibiotics), and producing reactive oxygen species (Cammarota 2012; Garcia 2014).

NAC can destabilise the biofilm structure, has synergic action with antibiotics, and bactericidal effects (Aslam 2007; Aslam 2011). Besides, NAC has a primary mucolytic effect by reducing the thickness of the gastric mucus layer and has antioxidant properties, both of which may exert beneficial adjuvant effects on H pylori eradication.

Helicobacter is capable of living as free micro‐organisms in gastric mucus, but more frequently they colonise and form biofilm ecosystems. This was demonstrated in vivo (Carron 2006; Coticchia 2006), and in vitro (Yonezawa 2010).

The Gurbuz 2005 trial showed positive results for antibiotics plus NAC, compared with placebo plus antibiotics. The Cammarota 2010 trial showed that pretreatment with NAC plus antibiotics was effective compared with antibiotics only in an open‐label randomised trial of 40 H pylori infected patients. The Hamidian 2015 trial, another randomised, placebo‐controlled trial, reported that infection was eradicated in 72.9% of patients in the experimental group (NAC plus antibiotic) and in 60.9% in the control group (antibiotics alone). However, there are some trials in patients which reported an additive effect on eradication rates with the use of NAC, although no statistical significance was detected (Karbasi 2013; Yoon 2015). The Hansen 1994 trial was a double‐blind trial, and observed no difference in eradication rates using NAC plus antibiotics. One open‐label trial showed similar eradication rates comparing NAC plus quadruple therapy (bismuth, amoxicillin, clarithromycin, and omeprazole) with the same quadruple therapy alone (Emami 2014).

We hypothesise that treatment failure may occur because of biofilm properties and resistant strains. NAC may have a role in first‐line and rescue therapies because of its properties in biofilm formation. This Cochrane Review intends to examine if NAC, used as an adjuvant to antibiotics, has a benefit in H pylori eradication rates. If so, this could change current practice.

Why it is important to do this review

H pylori infection is a major problem of public health and one of the most common infectious disease worldwide. This infection is associated with conditions of high morbidity and mortality, poor quality of life and high costs to healthcare systems. Although several regimens to eradicate H pylori are available, resistance to antibiotics is rising around the world, leading to unacceptable intention‐to‐treat eradication rates for an infectious disease.

Biofilm formation can be a hurdle to H pylori eradication (Cammarota 2012). NAC as an adjuvant therapy, is used in an attempt to enhance success in eradication rates (Ermis 2015).

The current literature shows some contradictory results for the efficacy of NAC as an adjuvant to antibiotics to eradicate H pylori. While some authors have found positive effects (Cammarota 2010; Gurbuz 2005), others have found no effect, or worsening results, when NAC is combined with antibiotics compared with antibiotics only (Hansen 1994; Karbasi 2013).

We are conducting this Cochrane Review to explore the uncertainty arising from conflicting results from studies in this area.

Objectives

To assess the efficacy and safety of N‐acetylcystein (NAC) as an adjuvant therapy to antibiotics for Helicobacter pylori (H pylori) eradication.

Methods

Criteria for considering studies for this review

Types of studies

We will include randomised controlled trials (RCTs). We will include studies reported as full text, those published as abstract only, and unpublished data.

We will not include cluster‐randomised, cross‐over design, and quasi‐randomised controlled trials.

Types of participants

We will include adults (over 16 years old) with a diagnosis of Helicobacter pylori (H pylori) infection, confirmed by urea breath test, stool antigen test, validated immunoglobulin G (IgG), serology, endoscopic biopsies with rapid urease reaction, histology, or culture. We will include patients in first‐, second‐ or third‐line eradication therapy.

Types of interventions

We will include trials comparing any antibiotic regimen plus NAC (intervention group) with the same antibiotic regimen without NAC (control group). In the control group, we will include trials with a placebo replacing the NAC, as well as trials of antibiotic regimens alone (without placebo).

We will include studies in which NAC was offered by any route of administration (orally or intravenously) and with any dose of NAC, provided the same route and the same dose were used in both experimental and control groups.

We will include studies with any drug, dose, or duration of antibiotic regimen provided they were equal in both groups.

We will include studies with any drug, dose, or duration of proton pump inhibitor (PPI) when they were part of the eradication therapy tested, provided they were equal in both groups.

Types of outcome measures

Primary outcomes

The primary outcomes will be:

1. successful H pylori eradication; and

2. gastrointestinal adverse events (e.g. diarrhoea, nausea, vomiting, or any other reported adverse event).

H pylori eradication will be defined as a negative test, at least four weeks after treatment, confirmed by urea breath test, stool antigen test, endoscopic biopsies with rapid urease reaction, histology, or culture. We will exclude studies that used serology to confirm eradication and/or studies where eradication was confirmed by a test performed within four weeks of treatment, as this could lead to misleading test results (Malfertheiner 2012).

In case any trial reports outcomes at more than one time point, we will consider the last available follow‐up.

We plan to contact trial authors if a trial has not reported eradication rates.

Reporting of the primary outcomes listed here will not be an inclusion criterion for the review.

Secondary outcomes

Secondary outcomes will be:

1. allergic adverse events (cutaneous rash, pruritus, or any other reported adverse event); and

2. toxic adverse events (hypotension, headache, anaphylactoid reactions, fever, or any other reported adverse event).

We will collect reports of adverse events, regarding the number and type of events (allergic, toxic, etc.), proportions of participants, and interference in compliance. We will analyse each type of adverse event separately.

Reporting of the secondary outcomes listed here will not be an inclusion criterion for the review.

Search methods for identification of studies

Electronic searches

We will conduct a literature search to identify all published and unpublished RCTs. The literature search will identify potential studies in all languages and with no limits to the year of publication. We will translate the non‐English language papers and fully assess them for potential inclusion in the review as necessary.

We will search the following electronic databases for identifying potential studies.

• Cochrane Central Register of Controlled Trials (CENTRAL) (Appendix 2).

• MEDLINE (1966 to present) (Appendix 3).

• Embase (1988 to present) (Appendix 4).

• CINAHL (1982 to present) (Appendix 5).

• LILACS (1982 to present).

Searching other resources

We will check reference lists of all primary studies and review articles for additional references.  We will contact authors of identified trials and ask them to identify other published and unpublished studies. We will also contact manufacturers and experts in the field.

We will search for errata or retractions from eligible trials on PubMed and report the date this was done within the review. We will search the grey literature databases and clinical trials registers below.

Grey literature databases

• Health Management Information Consortium (HMIC) database (www.ovid.com/site/catalog/DataBase/99.jsp)

• National Technical Information Service (NTIS) database (ntis.gov/products/ntisdb.aspx)

• OpenGrey (opengrey.eu)

Clinical trials registers/trial result registers

• AstraZeneca Clnical Trials

• Bristol‐Myers Squibb Clinical Trial Registry

• ClinicalTrials.gov

• Current Controlled Trials metaRegister of Controlled Trials (mRCT)

  • active registers (controlled‐trials.com/mRCT)

  • archived registers (controlled‐trials.com/mrct/archived)

• Eli Lilly and Company Clinical Trial Registry

  • lillytrials.com

  • lillytrials.com/initiated

• EU Clinical Trials Register

• GlaxoSmithKline Clinical Study Register

• International Clinical Trials Registry Platform Search Portal

• International Federation of Pharmaceutical Manufacturers and Associations (IFPMA) Clinical Trials Portal

• Roche Clinical Trials Results Database

Data collection and analysis

Selection of studies

Two review authors (LESF, CSB) will independently screen titles and abstracts for inclusion of all the potential studies we identify as a result of the search, and code them as 'retrieve' (eligible or potentially eligible/unclear) or 'do not retrieve'. We will retrieve the full‐text study reports/publication, and two review authors (LESF, CSB) will independently screen the full text and identify studies for inclusion and identify and record reasons for exclusion of the ineligible studies. We will resolve any disagreement through discussion or, if required, we will consult a third review author (RR). We will identify and exclude duplicates and collate multiple reports of the same study so that each study rather than each report is the unit of interest in the review. We will record the selection process in sufficient detail to complete a PRISMA flow diagram (Moher 2009), and 'Characteristics of excluded studies' table.

Data extraction and management

We will use a Cochrane standard data collection form (ERC 2014) for study characteristics and outcome data which has been piloted on at least one study in the review. Two review authors (LESF, CGZ) will extract study characteristics from the included studies. We will extract the following study characteristics.

1. Miscellaneous details of the study: report title, year of publication, author contacts, and publication type (abstract or full report).

2. Methods: Aim of study, study design, unit of allocation, start date, end date, duration of participation, and ethical approval.

3. Participants: Population description, setting, inclusion criteria, exclusion criteria, age, method of recruitment, informed consent obtained, total number randomised, baseline imbalances, withdrawals and exclusions, gender, race/ethnicity, severity of condition, comorbidities, diagnostic criteria, subgroups measured, subgroups reported, and other relevant sociodemographics.

4. Interventions: number randomised in each group, dose, duration of treatment period, timing, delivery, providers, co‐interventions, economic information, resource requirements, integrity of delivery, and compliance.

5. Outcomes: primary and secondary outcomes specified and collected, time points measured and reported, outcome definition, person measuring/reporting, unit of measurement, scales, imputation of missing data, assumed risk estimates, and power.

6. Notes: funding for trial, and notable conflicts of interest of trial authors

Two review authors (LESF, CGZ) will independently extract outcome data form included studies. We will note in the 'Characteristics of included studies' table if outcome data were reported in an unusable way. We will resolve disagreements by consensus or by involving a third review author (RR). One review author (LESF) will copy across the data from the data collection form into the Review Manager 5 file (RevMan 2014). We will double‐check that the data are entered correctly by comparing the study reports with how the data are presented in the review. A second review author will spot‐check study characteristics for accuracy against the trial report.

Assessment of risk of bias in included studies

Two review authors (LESF, ALCM) will independently assess the risk of bias for each study using the criteria outlined in the Cochrane Handbook for Systematic Reviews of Interventions (Higgins 2011). Any disagreement will be resolved by discussion or by involving a third review author (RR). We will assess the risk of bias according to the following domains.

1. Random sequence generation.

2. Allocation concealment.

3. Blinding of participants and personnel.

4. Blinding of outcome assessment.

5. Incomplete outcome data.

6. Selective outcome reporting.

7. Other bias.

We will grade each potential source of bias as high, low, or unclear, and provide a quote form the study report together with a justification for our judgment in the 'Risk of bias' table. We will summarise the risk of bias judgements across different studies for each of the domains listed. We will consider blinding separately for different key outcomes where necessary. Where information on risk of bias relates to unpublished data or correspondence with a trialist, we will note this in the 'Risk of bias' table.

When considering treatment effects, we will take into account the risk of bias for the studies that contribute to that outcome.

Assessment of bias in conducting the review

We will conduct the review according to this published protocol and report any deviations from it in the 'Differences between protocol and review' section of the review.

Measures of treatment effect

We will analyse dichotomous data as risk ratios and continuous data as a mean differences or standardised mean differences, providing 95% confidence intervals for the results. We will ensure that higher scores for continuous outcomes have the same meaning for the particular outcome, explain the direction to the reader, and report where the directions were reversed, if this was necessary.

We will undertake meta‐analyses only where this is meaningful, i.e. if the treatments, participants, and the underlying clinical question are similar enough for pooling to make sense.

A common way that trialists indicate when they have skewed data is by reporting medians and interquartile ranges. When we encounter this, we will note that the data are skewed and consider the implication of this.

Where multiple trial arms are reported in a single trial, we will include only the relevant arms. If two comparisons (e.g. drug A versus placebo and drug B versus placebo) must be entered into the same meta‐analysis, we will halve the control group to avoid double‐counting.

Unit of analysis issues

The unit of analysis will be the individual, with a single measurement of each outcome for each participant being collected and analysed.

Dealing with missing data

We will contact investigators or study sponsors to verify key study characteristics and obtain missing numerical outcome data where possible (e.g. when a study is identified as abstract only). If we cannot obtain the numerical outcome data, we plan to carry out an intention‐to‐treat analysis, assuming that missing participants have failed the treatment.

Assessment of heterogeneity

We will use the I² statistic to measure heterogeneity among the trials in each analysis (Higgins 2003). If we identify substantial heterogeneity, we will explore it by prespecified subgroup analysis. We will investigate statistical diversity by estimates of treatment effect through forest plots produced by Review Manager 5 software (RevMan 2014). We will consider an I² value greater than 50% as substantial heterogeneity (Higgins 2011). In this case, we will use a random‐effects model, rather than a fixed‐effect model.

Assessment of reporting biases

We will attempt to contact study authors, asking them to provide missing outcome data. Where this is not possible, and the missing data are thought to introduce serious bias, we will explore the impact of including such studies in the overall assessment of results by a sensitivity analysis. 

If we can pool more than 10 trials, we will create and examine a funnel plot to explore possible publication biases.

Data synthesis

We will combine the results across studies, undertaking a fixed‐effect model meta‐analysis for dichotomous and continuous outcomes if participants, interventions, comparisons, and outcomes are sufficiently similar to make clinical sense.

Subgroup analysis and investigation of heterogeneity

We plan to carry out the following subgroup analyses.

1. Patients in second‐line therapy.

2. Patients in third‐line therapy.

3. Type of test used to assess eradication:

   1. urea breath test

   2. stool antigen test

   3. endoscopic methods.

We will use the outcome of successful eradication rate in subgroup analysis. We will use the I² statistic to measure heterogeneity among the subgroups in each analysis. If we identify substantial heterogeneity ( > 50 %), we will explore it by the above prespecified subgroup analysis. Additionally, in case of substantial heterogeneity, we will use a random‐effects model rather than a fixed‐effect model.

Sensitivity analysis

We will perform sensitivity analysis, defined a priori, to assess the robustness of our conclusions. This will involve excluding trials with a high risk of bias (those classified as high risk in at least one of these criteria: randomisation, allocation concealment, and blinding).

Reaching conclusions

We will base our conclusions only on findings from the quantitative or narrative synthesis of included studies for this review. We will avoid making recommendations for practice if the results of the review are not statistically significant, and our implications for research will give the reader a clear sense of where the focus of any future research in the area should be, and what the remaining uncertainties are.

'Summary of findings' table

We will create a 'Summary of findings' table for each comparison below.

• Standard clarithromycin‐based triple therapy plus NAC versus standard clarithromycin‐based triple alone.

• Bismuth quadruple therapy plus NAC versus bismuth quadruple therapy alone.

• Sequential therapy plus NAC versus sequential therapy alone.

• Concomitant therapy plus NAC versus concomitant therapy alone.

• Hybrid therapy plus NAC versus hybrid therapy alone.

• Quinolone‐based therapy plus NAC versus quinolone‐based therapy alone.

Definitions for these regimens are the following.

• Standard clarithromycin triple therapy = PPI + clarithromycin + amoxicillin (7 to 14 days).

• Bismuth quadruple therapy = PPI + bismuth + tetracycline + metronidazole (10 to 14 days).

• Sequential therapy = PPI + amoxicillin (5 days), followed by PPI + clarithromycin + amoxicillin (5 days).

• Concomitant therapy = PPI + clarithromycin + metronidazole + amoxicillin (7 to 10 days).

• Hybrid therapy = PPI + amoxicillin (10 days), followed by PPI + clarithromycin + metronidazole + amoxicillin (10 days).

• Quinolone‐based therapy = PPI + quinolone + amoxicillin (10 days).

We will assess the body of the evidence for all pre‐defined outcomes: successful H pylori eradication, adverse events (gastrointestinal, cutaneous, toxic, and other serious adverse events). We will use the five GRADE considerations (study limitations, consistency of effect, imprecision, indirectness, and publication bias) to assess the quality of a body of evidence as it relates to the studies which contribute data to the meta‐analyses for the prespecified outcomes. We will use methods and recommendations described in Section 8.5 and Chapter 12 of the Cochrane Handbook for Systematic Reviews of Interventions (Higgins 2011), and use GRADEpro GDT (GRADEpro GDT 2014). We will justify all decisions to down‐ or upgrade the quality of studies using footnotes, and make comments to aid reader's understanding of the review where necessary. We will consider whether there is any additional outcome information that was not able to be incorporated into meta‐analyses, note this in the comments, and state if it supports or contradicts the information from the meta‐analyses.

Appendices

Appendix 1. Glossary of terms

Acetylated: product of a chemical reaction.

Adjuvant therapy: therapy that is given in addition to the primary therapy

Antagonist: a substance that acts against and blocks an action

Antioxidant: a substance that blocks or neutralises oxidation.

Atrophic gastritis: a pre‐cancerous type of inflammation of the lining of the stomach, characterised by the wasting away of stomach glands.

Atrophy: the wasting away, or decrease in size of something.

Bactericidal: capable of killing bacteria.

Beta‐lactamases: enzymes which give resistance to a group of antibiotics, so‐called beta‐lactams.

Bioavailability: the degree to which a substance is absorbed.

Biopsies: the removal and examination of small tissue, cell, or fluid samples.

Bismuth: a type of chemical substance with antimicrobial properties.

Campylobacter: a genus of bacteria.

Chronic: long‐term.

Cleavage: the breaking down into smaller components.

Culture: a method to cultivate bacteria.

Cutaneous: skin‐related.

Compliance: a patient’s willingness to follow prescribed treatment.

Cultivable: capable of growth.

Detoxification: the removal of a poisonous substance from the body.

Diffusion: distribution.

Dyspepsia: indigestion.

Dyspeptic: related to indigestion.

Endoscopy: the insertion of a thin illuminated tube into a hollow internal organ to allow visualisation and the passage of small surgical instruments.

Epithelial cells: a protective lining of membranous tissue.

Extracellular polymeric matrix: a type of biological substance produced by bacteria that can survive under difficult conditions.

Eradication: destruction.

Faecal‐oral transmission: transfer characterised by the intake of food or water into the mouth that has been contaminated with bodily waste.

Free oxygen radical scavengers: substance that blocks toxins released by oxygen metabolism.

Gastric: related to the stomach.

Gastric aspirates: contents suctioned from the stomach.

Gastritis: inflammation of the lining of the stomach.

Genus: origin.

Glutathione: a protein with important biochemical properties to protect all body cells.

Gram‐negative microaerophilic spiral bacterium: a type of bacterium with a spiral shape, not reacting to a dye test to detect bacteria, and with the capacity to survive in low oxygen environments.

Histology: examination under a microscope.

Idiopathic: occurring suddenly.

IgG serology: a test in blood serum using immunoglobulin G.

In vivo: in the body.

In vitro: in an artificial environment outside the body.

Iron deficiency anaemia: a condition of low red blood cells.

Latent: capable of living in the body without showing visible symptoms.

Lesions: abnormal changes in the structure of an organ.

Mucosal‐asssociated lymphoid tissue (MALT) lymphoma): a type of stomach cancer.

Metabolites: product of body's metabolism.

Morbidity: degree of illness or disease.

Mortality: death rate.

Mucolytic: tending to break down the thickness of human and animal secretions and tissues such as saliva and the lining of the stomach.

Oral‐oral transmission: transfer by the exchange of secretions (e.g. saliva, vomiting) of one person’s mouth to another person’s mouth.

Oxidative: product of chemical reaction, so‐called oxidation.

Pathogen: a micro‐organism capable of causing disease.

Peptic: related to the digestive tract.

Plasma: the fluid part of blood.

Proliferate: grow.

Pruritus: itching.

Proton pump inhibitor (PPI): a medication that lowers stomach acid production.

Rapid urease reaction: a test used to detect urea in gastric specimens.

Reactive oxygen species: toxic substances which are products of normal metabolism and could cause cellular damage.

Refractory: resistant to treatment or cure.

Stool antigen test: a laboratory test that detects parts of bacteria and serves to demonstrate its presence.

Streptococcus mutans: one species of bacteria which colonises humans.

Synergic: working together.

Synthesis: creating something whole by combining other smaller parts.

Thrombocytopenia purpura: a condition where purplish discolorations occur due to excessive bleeding into the skin and mucous membranes from the inability of the blood to clot.

Toxicity: poisoning.

Urea breath test: a laboratory test to detect the presence of urea in expired breath and to confirm the presence of Helicobacter pylori (H pylori).

Viable: capable of living.

Virulent: capable of being extremely dangerous or poisonous.

Viscosity: inability to flow.

Appendix 2. CENTRAL search strategy

Date Run: 04/11/15 20:54:22.311

ID Search Hits

#1 MeSH descriptor: [Helicobacter] explode all trees 1989

#2 MeSH descriptor: [Helicobacter Infections] explode all trees 1949

#3 helicobacter or pylori or pyloridis or "HP" or campylobacter:ti,ab,kw (Word variations have been searched) 5064

#4 #1 or #2 or #3 5064

#5 MeSH descriptor: [Acetylcysteine] explode all trees 612

#6 acetylcystein* or (acetyl near/2 cistein*) or (acetyl near/2 cystein*):ti,ab,kw (Word variations have been searched) 1261

#7 NAC or Mucomyst or Acetadote or cilol or flumucil or Gluton or Mucare or mucinac:ti,ab,kw (Word variations have been searched) 701

#8 mucohelp or mucomelt or mucomix or mucosys or mucotyle or mucyst or nacel or nacfil:ti,ab,kw (Word variations have been searched) 0

#9 Genac or Solmucol or Acetabs or Acetyst or Airbron or Alveolex or Azubronchin or Bromuc:ti,ab,kw (Word variations have been searched) 0

#10 Broncho Fips or BronchoFips or Broncholysin or Broncoclar or Codotussyl or Cystamucil:ti,ab,kw (Word variations have been searched) 0

#11 Dampo Mucopect or durabronchal or Eurespiran or Exomuc or Fabrol or Fluprowit or Muco Sanigen:ti,ab,kw (Word variations have been searched) 4

#12 Frekatuss or Hoestil or Ilube or Jenacystein or Jenapharm or Lantamed or Lindocetyl or M‐Pectil or M Pectil or MPectil:ti,ab,kw (Word variations have been searched) 3

#13 Muciteran or Acetylin or Mucosil or Mucosol or Mucosolvin or Siccoral or Siran or acebraus:ti,ab,kw (Word variations have been searched) 4

#14 acerac or acetain or acypront or acys‐5 or brunac or cetilan or drenaflen or ecomucyl or encore or flemex‐ac:ti,ab,kw (Word variations have been searched) 42

#15 fluimicil or fluimucil or fluimukan or flutafin or hidonac or inspire or lappe or libramucil or menaxol or mercapturic acid:ti,ab,kw (Word variations have been searched) 1497

#16 mucocil or mucofillin or mucolator or mucomiste or mucoserin or mucosof or mucosten or mucoza or mukolit:ti,ab,kw (Word variations have been searched) 0

#17 muteran or parvolex or reolin or respaire or sigamucil or siran 200 or spatam or sputoprompt or stecin or tixair or zifluvis:ti,ab,kw (Word variations have been searched) 0

#18 #5 or #6 or #7 or #8 or #9 or #10 or #11 or #12 or #13 or #14 or #15 or #16 or #17 2916

#19 #4 and #18 14

Appendix 3. MEDLINE search strategy

Database: Ovid MEDLINE(R) In‐Process & Other Non‐Indexed Citations and Ovid MEDLINE(R) <1946 to Present>

Search Strategy:

‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐

1 exp Helicobacter/ or exp Helicobacter infection/ (33279)

2 (helicobacter or pylori or pyloridis or "HP" or campylobacter).ti,ab,kw. (64294)

3 1 or 2 (66915)

4 exp Acetylcysteine/ (11078)

5 (acetylcystein* or (acetyl adj2 cistein*) or (acetyl adj2 cystein*)).tw,kw. (15547)

6 (NAC or Mucomyst or Acetadote or cilol or flumucil or Gluton or Mucare or mucinac).tw,kw. (12595)

7 (mucohelp or mucomelt or mucomix or mucosys or mucotyle or mucyst or nacel or nacfil).tw,kw. (0)

8 (Genac or Solmucol or Acetabs or Acetyst or Airbron or Alveolex or Azubronchin or Bromuc).tw,kw. (4)

9 (Broncho Fips or BronchoFips or Broncholysin or Broncoclar or Codotussyl or Cystamucil).tw,kw. (2)

10 (Dampo Mucopect or durabronchal or Eurespiran or Exomuc or Fabrol or Fluprowit or Muco Sanigen).tw,kw. (6)

11 (Frekatuss or Hoestil or Ilube or Jenacystein or Jenapharm or Lantamed or Lindocetyl or M‐Pectil or M Pectil or MPectil).tw,kw. (36)

12 (Muciteran or Acetylin or Mucosil or Mucosol or Mucosolvin or Siccoral or Siran or acebraus).tw,kw. (28)

13 (acerac or acetain or acypront or acys‐5 or brunac or cetilan or drenaflen or ecomucyl or encore or flemex‐ac).tw,kw. (157)

14 (fluimicil or fluimucil or fluimukan or flutafin or hidonac or inspire or lappe or libramucil or menaxol or mercapturic acid).tw,kw. (2902)

15 (mucocil or mucofillin or mucolator or mucomiste or mucoserin or mucosof or mucosten or mucoza or mukolit).tw,kw. (0)

16 (muteran or parvolex or reolin or respaire or sigamucil or siran 200 or spatam or sputoprompt or stecin or tixair or zifluvis).tw,kw. (6)

17 or/4‐16 (27714)

18 3 and 17 (58)

19 remove duplicates from 18 (56)

Appendix 4. EMBASE search strategy

Database: Embase <1974 to 2015 November 03>

Search Strategy:

‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐

1 exp Helicobacter/ or exp Helicobacter infection/ (55182)

2 (helicobacter or pylori or pyloridis or "HP" or campylobacter).ti,ab,kw. (82108)

3 1 or 2 (91470)

4 exp acetylcysteine/ (27713)

5 (acetylcystein* or (acetyl adj2 cistein*) or (acetyl adj2 cystein*)).tw,kw. (19474)

6 (NAC or Mucomyst or Acetadote or cilol or flumucil or Gluton or Mucare or mucinac).tw,kw. (17114)

7 (mucohelp or mucomelt or mucomix or mucosys or mucotyle or mucyst or nacel or nacfil).tw,kw. (1)

8 (Genac or Solmucol or Acetabs or Acetyst or Airbron or Alveolex or Azubronchin or Bromuc).tw,kw. (45)

9 (Broncho Fips or BronchoFips or Broncholysin or Broncoclar or Codotussyl or Cystamucil).tw,kw. (23)

10 (Dampo Mucopect or durabronchal or Eurespiran or Exomuc or Fabrol or Fluprowit or Muco Sanigen).tw,kw. (31)

11 (Frekatuss or Hoestil or Ilube or Jenacystein or Jenapharm or Lantamed or Lindocetyl or M‐Pectil or M Pectil or MPectil).tw,kw. (185)

12 (Muciteran or Acetylin or Mucosil or Mucosol or Mucosolvin or Siccoral or Siran or acebraus).tw,kw. (128)

13 (acerac or acetain or acypront or acys‐5 or brunac or cetilan or drenaflen or ecomucyl or encore or flemex‐ac).tw,kw. (476)

14 (fluimicil or fluimucil or fluimukan or flutafin or hidonac or inspire or lappe or libramucil or menaxol or mercapturic acid).tw,kw. (3987)

15 (mucocil or mucofillin or mucolator or mucomiste or mucoserin or mucosof or mucosten or mucoza or mukolit).tw,kw. (16)

16 (muteran or parvolex or reolin or respaire or sigamucil or siran 200 or spatam or sputoprompt or stecin or tixair or zifluvis).tw,kw. (83)

17 or/4‐16 (42667)

18 3 and 17 (137)

19 remove duplicates from 18 (136)

Appendix 5. CINAHL search strategy

#	Query	Results
S18	S3 AND S17	21
S17	S4 OR S5 OR S6 OR S7 OR S8 OR S9 OR S10 OR S11 OR S12 OR S13 OR S14 OR S15 OR S16	3,368
S16	TX muteran or parvolex or reolin or respaire or sigamucil or siran 200 or spatam or sputoprompt or stecin or tixair or zifluvis	0
S15	TX mucocil or mucofillin or mucolator or mucomiste or mucoserin or mucosof or mucosten or mucoza or mukolit	0
S14	TX fluimicil or fluimucil or fluimukan or flutafin or hidonac or inspire or lappe or libramucil or menaxol or mercapturic acid	1,905
S13	TX acerac or acetain or acypront or acys‐5 or brunac or cetilan or drenaflen or ecomucyl or encore or flemex‐ac	124
S12	TX Muciteran or Acetylin or Mucosil or Mucosol or Mucosolvin or Siccoral or Siran or acebraus	17
S11	TX Frekatuss or Hoestil or Ilube or Jenacystein or Jenapharm or Lantamed or Lindocetyl or M‐Pectil or M Pectil or MPectil	1
S10	TX Dampo Mucopect or durabronchal or Eurespiran or Exomuc or Fabrol or Fluprowit or Muco Sanigen	0
S9	TX Broncho Fips or BronchoFips or Broncholysin or Broncoclar or Codotussyl or Cystamucil	0
S8	TX Genac or Solmucol or Acetabs or Acetyst or Airbron or Alveolex or Azubronchin or Bromuc	0
S7	TX mucohelp or mucomelt or mucomix or mucosys or mucotyle or mucyst or nacel or nacfil	0
S6	TX NAC or Mucomyst or Acetadote or cilol or flumucil or Gluton or Mucare or mucinac	505
S5	TX acetylcystein* or (acetyl and cistein*) or (acetyl and cystein*)	1,050
S4	(MH "Acetylcysteine")	703
S3	S1 OR S2	8,709
S2	TX helicobacter or pylori or pyloridis or "HP" or campylobacter	8,709
S1	(MH "Helicobacter+") OR (MH "Helicobacter Infections")	2,280

Contributions of authors

• Conceiving the protocol: LESF

• Designing the protocol: LESF, RR

• Co‐ordinating the protocol: LESF

• Designing search strategies: Information Specialist of the UGPD Group

• Writing the protocol: LESF, RR

• Providing general advice on the protocol: RR

• Securing funding for the protocol: LESF

• Performing previous work that was the foundation of the current study: LESF

Declarations of interest

None of the review authors are sponsored, employed, or involved in clinical trials of antimicrobial Helicobacter pylori (H pylori) therapy, or the manufacture or use of N‐acetylcysteine (NAC).

• LEF: none known.

• CB: none known.

• ALM: none known.

• CGZ: none known.

• RR: none known.

New