Efficacy and safety of Saccharomyces boulardii as adjunct therapy with Vancomycin in treating Clostridioides difficile infection: A randomized controlled trial

Abstract

Clostridioides difficile infection (CDI) is a significant cause of hospital-acquired diarrhea, leading to high morbidity, recurrence, and healthcare costs. Probiotics like Saccharomyces boulardii show potential as an adjunct therapy to standard CDI treatment, but further trials are needed to confirm their efficacy. This study assessed the efficacy and safety of S. boulardii combined with vancomycin for treating mild to moderate CDI. 120 CDI patients diagnosed with positive stool toxin test were randomly assigned to receive two capsules of 250 mg of S. boulardii or a placebo every 12 h alongside 125 mg of vancomycin every 6 h for 10 days. The primary endpoint was the clinical cure rate, with secondary endpoints including recurrence, global cure rate, and diarrheal outcomes. Clinical cure rates were similar between groups (98.4% vs. 98.3%), but the combination group had a significantly higher global cure rate (96.6% vs. 85.3%, p = 0.044) and lower recurrence rate (1.7% vs. 13.1%, p = 0.032). No significant differences were found in diarrheal outcomes, functional ability, or adverse events. No patients discontinued treatment due to intolerance. In conclusion, adding S. boulardii to vancomycin reduced CDI recurrence without affecting functional recovery or increasing adverse events.

Introduction

Clostridioides difficile infection (CDI) is a significant cause of nosocomial diarrhea, particularly among hospitalized patients. It is associated with substantial morbidity, extended hospital stays, and increased healthcare costs¹. Despite effective initial treatment with antibiotics such as vancomycin or fidaxomicin, CDI has a high recurrence rate, with some studies reporting rates as high as 20–30%^2,3. Current treatment options primarily focus on antibiotics, which can disrupt the gut microbiome and contribute to recurrence. Therefore, there is a pressing need for additional therapies to enhance treatment outcomes and reduce recurrence rates^4,5.

Probiotics, particularly Saccharomyces boulardii, have shown potential in preventing and treating CDI by restoring gut microbiota balance and inhibiting pathogen colonization. S. boulardii, a non-pathogenic yeast, has been extensively studied for its benefits in various gastrointestinal disorders, including CDI^6,7. Research suggests that administering S. boulardii alongside standard antibiotic therapy may enhance treatment efficacy and significantly reduce CDI recurrence^8,9. Emerging microbiota restoration therapies such as RBX2660 and SER-109 have also shown promising results in decreasing CDI recurrence rates^10,11. While several studies have investigated the efficacy of probiotics with standard antibiotic treatment for CDI, findings remain mixed, highlighting the need for further research to draw definitive conclusions¹². Robust clinical trials are essential to confirm the effectiveness and safety of S. boulardii and other probiotic interventions in CDI management¹³.

This study aims to evaluate the efficacy and safety of S. boulardii in conjunction with vancomycin for treating mild to moderate CDI. Unlike previous studies, this research focuses on the adjunctive use of probiotics during active treatment rather than solely on prevention. We believe that this combination therapy has the potential to improve clinical cure rates and reduce the recurrence of CDI, offering a promising avenue for future treatment.

Materials and methods

Study design

This prospective, double-blind, randomized, placebo-controlled trial was conducted from November 2021 to November 2023, adhering to the ethical principles of the Declaration of Helsinki and current Good Clinical Practices. The Chiang Mai University review boards approved the study protocol and amendments (Study Code: MED-2564–08655). All patients provided written informed consent.

Study population

Patients were enrolled at Chiang Mai University Hospital, Chiang Mai, Thailand. Eligible hospitalized patients were 20 years or older with a diagnosis of mild to moderate CDI⁴ defined by the presence of nosocomial diarrhea (more than three unformed bowel movements in 24 h) and detection of C. difficile either toxin A or B in a stool sample obtained within 48 h before randomization. The exclusion criteria for the study were as follows: individuals diagnosed with severe CDI, indicated by a white blood cell count greater than 15,000 cells/mm³; an acute increase in serum creatinine levels exceeding 50% above baseline; a body temperature above 38.5 °C; or evidence of severe colitis as determined by clinical examination or imaging. Additional exclusions included a prior history of CDI, the presence of other known causes of diarrhea, chronic intestinal diseases such as inflammatory bowel disease or irritable bowel syndrome, abdominal surgery within the past three months, a severely immunocompromised state, pregnancy, inability to attend follow-up appointments, and patients who were regular users of probiotics and unwilling to discontinue their use. These criteria were established to ensure participant safety and the integrity of the study results.

Randomization and treatment

After obtaining informed consent, patients were randomly assigned in a 1:1 ratio using permuted blocks of four. They received the study medication orally for ten days: 250 mg of S. boulardii CNCM I-745 or a placebo, administered as two capsules every 12 h, along with 125 mg of vancomycin every 6 h as standard CDI antibiotic treatment for mild to moderate CDI. Both S. boulardii CNCM I-745 and the placebo were over-encapsulated to appear identical. Patients were assessed daily for clinical cure and treatment failure throughout the 10-day treatment period. Participants maintained daily stool diaries submitted during clinic visits on Days 0, 28, and 56. Following the achievement of a clinical cure, patients were monitored for recurrence through daily stool diary evaluations for 56 days after the final dose of the study medication. Stool testing for C. difficile toxin was conducted for patients who exhibited new or worsening symptoms following therapy⁴.

Definitions

Clinical cure was defined as complete cessation or reduction (three or fewer unformed stools for two consecutive days) of diarrhea and other associated symptoms, such as abdominal pain, and maintaining this resolution throughout therapy, with no further treatment needed for CDI by the second day after therapy ended³. The persistence of diarrhea, the need for additional therapy for CDI, or both defined clinical failure. Global cure meant resolving diarrhea without recurrence. Patients were monitored for recurrence up to 56 days post-randomization. Clinical recurrence was defined as more than three diarrheal stools per 24 h within eight weeks after therapy ended, the presence of C. difficile toxin A or B in stool, and the need for retreatment.

The diarrhea outcomes were determined after data collection but before unblinding the treatment allocation. The duration of diarrhea was defined as the number of consecutive 24-hour periods with diarrhea that occurred after study enrollment, starting from the first stool diary day¹⁴. Total diarrhea days were the cumulative days those participants experienced diarrhea. The rate of diarrhea was calculated as the total diarrhea days divided by the total number of stool diary days. Functional capacity was assessed using the Barthel Index, a widely used measure of functional independence, on days 1, 28, and 56 to provide a comprehensive understanding of the patient’s functional status during the study.

Outcome measures

The primary endpoint was the rate of clinical cure in the intention-to-treat and per-protocol populations at the end of therapy or at the time of withdrawal from the study. The intention-to-treat population included patients with documented CDI who were randomized and received at least one dose of study medication. The per-protocol population included patients in the intention-to-treat group who received treatment for at least three days (for treatment failure) or eight days (for clinical cure), adhered to the protocol, and underwent an end-of-therapy evaluation³. The secondary endpoints included recurrence of CDI, global cure in the intention-to-treat and per-protocol populations, and diarrheal outcomes.

Safety

Safety was assessed from the day informed consent was given until the last dose of the study drug or the final study visit, whichever was later. Assessments included comprehensive physical exams, ECGs, and lab tests (hematologic, biochemical, and urinalysis). The safety population included patients who received at least one dose of the study drug and had one safety assessment post-dose. Adverse events were classified per the Medical Dictionary for Regulatory Activities, with each patient counted once per event type.

Statistical analysis

Primary outcomes were analyzed using Stata Statistical Software (version 16.1, StataCorp LLC, College Station, TX) with intention-to-treat and per-protocol methodologies. Treatment arm comparisons were conducted using the Wilcoxon rank-sum test, χ² test, or Fisher’s exact test, with a significance level of 0.05, ensuring the validity and reliability of the results. This study was registered with the Thai Clinical Trials Registry (www.thaiclinicaltrials.org) under the number TCTR20241202006, with an initial registration date of 02/11/2021.

Results

A total of 1,102 potential participants with nosocomial diarrhea were evaluated for eligibility. Of these, 274 (24.86%) tested positive for stool C. difficile toxin A or B. Among the positive cases, 120 individuals met the study’s inclusion criteria, while the remaining 154 were excluded, primarily due to severe comorbid diseases and declining participation. Eligible participants were randomly assigned to one of two groups: 61 received vancomycin, and 59 received a combination of S. boulardii and vancomycin. Figure 1 illustrates the randomization process and follow-up. Two participants did not complete the study: one from the vancomycin group lost to follow-up, and one from the combination group discontinued treatment due to lack of interest. Consequently, 118 eligible participants completed the stool diary over eight weeks and were included in the analyses. Medication adherence was high in both treatment groups, with 100% in the intention-to-treat population, 98.36% in the vancomycin group, and 98.31% in the combination group in the per-protocol population.

Fig. 1.

The study flow diagram. ITT, intention to treat; PP, per protocol.

Baseline clinical characteristics

Table 1 shows the baseline characteristics of the patients enrolled in the treatment group. The participants had a mean age of 64.53 years, and 56.67% were female. Additionally, 81.67% of participants had underlying medical conditions, including diabetes mellitus (20%), ischemic heart disease (22.25%), chronic obstructive pulmonary disease (23.33%), and chronic kidney disease (25%). There were no significant differences between the groups regarding female proportion, mean age, median length of stay, previous admissions, BMI, comorbidities, clinical symptoms, antibiotic and PPI usage, and baseline laboratory results, suggesting that the two groups were well-matched at baseline (Table 1).

Table 1.

Participants demographics and baseline characteristics.

Parameter	Total (n = 120)	Vancomycin (n = 61)	S. boulardii and vancomycin (n = 59)	p-value
Male, n (%)	52 (43.33)	30 (49.18)	22 (37.29)	0.297
Age, mean ± SD	64.53 ± 19.10	60.77 ± 21.05	68.30 ± 16.44	0.128
LOS, median (IQR)	17 (10–32)	19 (10–35)	14 (9–28)	0.214
Previous admission in 90 days, n (%)	34 (28.33)	21 (34.42)	13 (22.03)	0.559
BMI, mean ± SD	22.83 ± 4.73	22.89 ± 4.88	22.77 ± 4.67	0.919
Comorbidities, n (%)	98 (81.67)	44 (72.13)	54 (91.53)	0.181
Diabetes mellitus	24 (20.00)	12 (19.67)	12 (20.33)	0.381
Ischemic heart disease	27 (22.25)	13 (21.31)	14 (23.73)	0.425
Chronic obstructive pulmonary disease	28 (23.33)	14 (22.95)	14 (23.73)	0.643
Chronic kidney disease	30 (25.00)	15 (24.59)	15 (25.42)	0.562
Medications, n (%)
History of PPI use	40 (33.33)	22 (36.06)	18 (30.51)	0.196
Ongoing antibiotic treatment	102 (85.00)	56 (91.80)	46 (77.97)	0.145
Symptoms, n (%)
Abdominal pain	32 (26.67)	18 (29.51)	14 (23.73)	0.559
Nausea, vomiting	22 (18.33)	14 (22.95)	8 (13.56)	0.181
GI bleeding	10 (8.33)	4 (6.78)	6 (9.83)	0.195
Laboratory, mean ± SD
Hb (g/dL)	11.79 ± 1.84	11.83 ± 2.14	11.74 ± 1.51	0.841
WBC	10,721 ± 4,336	11,287 ± 4,907	10,155 ± 3,674	0.316
Albumin (g/dL)	3.24 ± 0.43	3.34 ± 0.37	3.13 ± 0.47	0.068
eGFR	68.5 ± 11.1	67.4 ± 10.1	69.2 ± 12.2	0.225

Clinical outcomes

Table 2 compares the outcomes between the vancomycin group and the combination group. The clinical cure rates were similar in both groups, with no significant differences observed in the intention-to-treat (98.36% vs. 98.31%) or per-protocol analyses (100% vs. 100%). However, the combination group demonstrated significantly higher global cure rates. The intention-to-treat analysis showed a global cure rate of 96.61% for the combination group compared to 85.25% for the vancomycin group (p = 0.044). Similarly, the per-protocol analysis favored the combination group, with global cure rates of 98.28% versus 86.67% (p = 0.032).

Table 2.

Study outcomes.

Parameters	Vancomycin (n = 61)	S. boulardii and vancomycin (n = 59)	p-value
Duration of diarrhea (cumulative days), median (IQR)	5 (4–7)	4 (3–5)	0.483
Diarrhea rate (days of diarrhea/stool diary days submitted), median (IQR)	0.18 (0.16–0.21)	0.16 (0.14–0.19)	0.322
Total number of days with diarrhea (days), median (IQR)	10 (8–11)	9 (8–10)	0.069
Total Barthel Index score, median (IQR)
Day 1	22.5 (10–45)	25 (15–45)	0.628
Day 28	37.5 (15–65)	40 (20–50)	0.935
Day 56	57.5 (15–65)	50 (35–65)	0.847
Clinical cure
Intention-to-treat (%)	60 (98.36)	58 (98.31)	1.000
Per-protocol therapy (%)	60 (100)	58 (100)	1.000
CDI recurrence (%)
Intention-to-treat (%)	8 (13.11)	1 (1.69)	0.032
Per-protocol therapy (%)	8 (13.33)	1 (1.72)	0.031
Global cure
Intention-to-treat (%)	52 (85.25)	57 (96.61)	0.044
Per-protocol therapy (%)	52 (86.67)	57 (98.28)	0.032

Combination therapy significantly reduced CDI recurrence. The intention-to-treat analysis showed a recurrence rate of 1.69% in the combination group compared to 13.11% in the vancomycin group (p = 0.032). The per-protocol analysis yielded similar results (1.72% vs. 13.33%, p = 0.031). The median duration of diarrhea was one day longer in the vancomycin group, but this was not statistically significant (p = 0.483). Other outcomes, such as the total number of days with diarrhea and diarrhea rate, were more favorable with S. boulardii, though not statistically significant. Notably, there were no significant differences in functional ability at day 28 or 56, providing reassurance about the overall impact of the treatments. Adverse events were similar between groups, with mild gastrointestinal and nonspecific symptoms occurring at similar rates (9.7% vs. 9.0%). No subjects were discontinued due to intolerance or allergy.

Discussion

The results of this study suggest that combining S. boulardii with vancomycin offers superior outcomes in treating nosocomial diarrhea caused by CDI. Specifically, the combination therapy significantly reduces CDI recurrence and achieves a higher global cure rate compared to vancomycin alone. Additionally, combination therapy shortens the duration of diarrhea and reduces the total number of days patients experience diarrhea, thereby improving symptom management, enhancing patient comfort, and optimizing clinical outcomes. Importantly, this was achieved without any serious adverse events, supporting the safety of S. boulardii as an adjunct to standard antibiotic therapy.

While previous research has predominantly focused on probiotics as a preventive measure for initial and recurrent CDI¹⁴ the role of probiotics as adjunctive therapy for the initial treatment of CDI has received comparatively less attention. Studies on S. boulardii to prevent recurrent CDI have shown mixed results¹². While some findings suggest it may reduce recurrence risk, especially in patients receiving specific antibiotic regimens, its role in primary prevention remains uncertain, with limited supporting evidence^15,16. This study contributes to the growing body of evidence by demonstrating the potential benefits of adding S. boulardii to vancomycin for managing CDI. It provides robust evidence that this combination significantly lowers recurrence rates and enhances global cure rates, which are critical measures of long-term treatment success. Although adding S. boulardii did not significantly improve clinical cure rates, the marked reduction in recurrence and the enhanced global cure rates are essential findings with substantial clinical implications. The contrast between clinical and global cures highlights vancomycin’s limitation in addressing C. difficile spores, contributing to relapse¹⁷. By targeting the pathogen’s life cycle—suppressing spore germination¹⁷ toxin production¹⁸ and gut dysbiosis¹⁹—combination therapy with S. boulardii reduces recurrence rates and achieves more durable global cures, advancing long-term treatment outcomes.

The findings of this study suggest that incorporating probiotics like S. boulardii into CDI treatment protocols could offer substantial benefits for patient outcomes, including better management of symptoms and reduced recurrence rates. Such strategies could reduce healthcare costs by minimizing the need for additional treatments and hospitalizations, ultimately leading to more efficient and cost-effective care. Despite gastrointestinal disturbances being the most observed adverse event, no serious adverse events were reported, supporting the safety of S. boulardii as a clinically viable adjunctive therapy. Furthermore, the similar rates of adverse events between the treatment groups underscore that adding S. boulardii does not introduce significant safety concerns.

The mechanisms underlying the beneficial effects of S. boulardii in CDI are multifaceted. One key mechanism involves competition with C. difficile for essential nutrients and attachment sites in the gastrointestinal tract, which can limit C. difficile’s ability to proliferate²⁰. Additionally, S. boulardii produces antimicrobial substances such as acetic acid and antimicrobial peptides, which help inhibit the growth of C. difficile and other harmful microorganisms²¹. Furthermore, S. boulardii has been shown to modulate the immune response by enhancing the production of immunoglobulins and other immune factors, thereby supporting the body’s ability to fight infection²². S. boulardii also plays a role in neutralizing toxins produced by C. difficile, including protease enzymes that break down toxins A and B, further reducing the harmful effects of CDI²³.

While the study provides important insights, several limitations should be considered. The small sample size limits the generalizability of the findings, and further large-scale studies are needed to confirm these results and better understand the potential impact of S. boulardii in different patient populations and clinical settings. The study’s single-center nature also restricts the findings’ external validity, suggesting that multi-center trials would be beneficial to assess whether the results hold across different healthcare settings. Moreover, the study included only mild to moderate CDI patients, which may not reflect outcomes for those with severe CDI. While the probiotic group demonstrated more favorable outcomes regarding diarrhea duration, these differences were not statistically significant, indicating that additional research is needed to clarify the precise benefits of S. boulardii when combined with vancomycin. Future trials should prioritize serial microbiome fecal sampling to thoroughly investigate pathogen resistance, toxin expression, and bile salt metabolism —key factors in understanding the biological mechanisms underlying the observed clinical outcomes. Lastly, the lack of significant differences in functional status at weeks 4 and 8 suggests that the combination therapy may not substantially impact long-term functional recovery, warranting further investigation with more extended follow-up periods to assess the broader effects of treatment.

Conclusions

This study shows that adding S. boulardii to vancomycin therapy can reduce CDI recurrence and improve overall treatment outcomes. However, due to the study’s small sample size and potential confounders, further research is necessary to confirm these results and explore the long-term effects. Integrating S. boulardii into clinical practice could significantly enhance CDI treatment, leading to better patient outcomes and more efficient healthcare delivery.

Author contributions

T.C. was responsible for study design and conception, data acquisition, analysis, interpretation, and article drafting. U.W. helped with data acquisition and interpretation, statistical analysis, and article drafting. P.T., P.W., and P.S. helped in statistical analysis and manuscript drafting. All authors critically revised the article, approved the final version to be published, and agreed to be accountable for all aspects of the report.

Funding

This work was supported by the Faculty of Medicine, Chiang Mai University, grant no MC046-65.

Data availability

The datasets used and analyzed during the current study are available from the corresponding author upon reasonable request.

Declarations

Competing interests

The authors declare no competing interests.

Abbreviations

CDI, Clostridium difficile infection; PPI, proton pump inhibitor.

Ethical approval

The study conformed to the principles of the Declaration of Helsinki and Good Clinical Practice Guidelines. It was approved by the Research Ethics Committee of the Faculty of Medicine, Chiang Mai University (Study Code: MED-2564-08655).

Consent to participate

Patients received written and oral information on the study and consented to participate and have their medical data used for research purposes.