Search Article Keyword:  

PubMed Submission Abstract PDF Feed Back Count: 5693 Download Count: 2188 

ISSN 1007-9327 CN 14-1219/R  World J Gastroenterol  2008 May 7; 14(17): 2650-2661

TOPIC HIGHLIGHT

Meta-analysis of probiotics for the treatment of irritable bowel syndrome

Lynne V McFarland, Sascha Dublin


Lynne V McFarland, Department of Health Services Research and Development, VA Puget Sound Health Care System, Metropolitan Park West, 1100 Olive Way, Suite #1400, Seattle WA 98101, United States

Lynne V McFarland, Department of Medicinal Chemistry, School of Pharmacy, University of Washington, Seattle WA 98101,
United States

Sascha Dublin, Group Health Center for Health Studies, 1730 Minor Avenue, Suite 1600, Seattle 98101, United States

Author contributions: McFarland LV and Dublin S contributed equally to this work in the design of the research, analysis and writing of the paper.

Supported by Veterans' Affairs Health Services Research & Development fellowship, TPA 61-029 (Dr. Dublin), National Institute of Aging grant, AG028954-01A1 (Dr. Dublin)

Correspondence to: Lynne V McFarland, PhD, Department of Health Services Research and Development, VA Puget Sound Health Care System, Metropolitan Park West, 1100 Olive Way, Suite #1400, Seattle WA 98101,

United States. lynne.mcfarland@va.gov

Telephone: +1-206-2771095    Fax: +1-206-7642935

Received: December 19, 2007  Revised: January 29, 2008

  

Abstract

Irritable bowel syndrome (IBS) is a chronic condition affecting 3%-25% of the general population. As no curative treatment is available, therapy is aimed at reducing symptoms, often with little success. Because alteration of the normal intestinal microflora has been observed in IBS, probiotics (beneficial microbes taken to improve health) may be useful in reducing symptoms. This paper systematically reviews randomized, controlled, blinded trials of probiotics for the treatment of IBS and synthesizes data on efficacy across trials of adequate quality. PubMed, Medline, Google Scholar, NIH registry of clinical trials, metaRegister, and the Cochrane Central Register of Controlled Trials were searched from 1982-2007. We also conducted secondary searches of reference lists, reviews, commentaries, relevant articles on associated diseases, books and meeting abstracts. Twenty trials with 23 probiotic treatment arms and a total of 1404 subjects met inclusion criteria. Probiotic use was associated with improvement in global IBS symptoms compared to placebo [pooled relative risk (RRpooled) 0.77, 95% confidence interval (95% CI) 0.62-0.94]. Probiotics were also associated with less abdominal pain compared to placebo [RRpooled = 0.78 (0.69-0.88)]. Too few studies reported data on other IBS symptoms or on specific probiotic strains to allow estimation of a pooled RR. While our analyses suggest that probiotic use may be associated with improvement in IBS symptoms compared to placebo, these results should be interpreted with caution, given the methodological limitations of contributing studies. Probiotics warrant further study as a potential therapy for IBS.

 

© 2008 WJG. All rights reserved.

 

Key words: Probiotics; Meta-analysis; Irritable bowel syndrome

 

Peer reviewers: Francesco Costa, Dr, Dipartimento di Medicina Interna-U.O. di Gastroenterologia Università di Pisa-Via Roma, 67-56122-Pisa, Italy; Yvan Vandenplas, Professor, Department of Pediatrics, AZ-VUB, Laarbeeklaan 101, Brussels 1090, Belgium

 

McFarland LV, Dublin S. Meta-analysis of probiotics for the treatment of irritable bowel syndrome. World J Gastroenterol 2008; 14(17): 2650-2661  Available from: URL: http://www.wjgnet.com/1007-9327/14/2650.asp  DOI: http://dx.doi.org/10.3748/wjg.14.2650

  

INTRODUCTION

Irritable bowel syndrome (IBS) is a chronic condition that severely impacts the quality of life of affected individuals[1,2]. The prevalence of IBS in the general population ranges from 3%-25%[3]. IBS is characterized by intermittent abdominal pain, altered bowel habits (diarrhea and/or constipation) and other gastrointestinal symptoms such as bloating and flatulence in the absence of structural abnormalities in the intestine. The pathophysiology of IBS is multifactorial and may include motor and sensory dysfunction, immune responses, food sensitivities and genetic predisposition[3,4]. Risk factors include female gender (2-3 times more common), acute gastrointestinal infections (e.g. Campylobacter or Salmonella) and psychological factors[3,5,6]. As no curative treatments are available, therapy for IBS is palliative and supportive, targeting specific symptoms, but is notoriously unsatisfactory[7,8]. Although 30% of patients report resolution of symptoms within one year, nearly 70% report that symptoms recur within five years[3].

Studies have observed altered intestinal microflora in IBS patients and an increase in symptoms after enteric infections[9-12], suggesting that restoration of the intestinal microflora may be a useful therapeutic goal. One strategy to restore normal flora is the use of probiotics[13,14]. Probiotics are “beneficial bacteria or yeasts that are ingested to improve health”[15]. Probiotics are also known to modulate the immune response and reduce cytokine production[9,16-18]. Strong evidence for the beneficial role of probiotics exists for the prevention of antibiotic-associated diarrhea, traveler’s diarrhea and pediatric diarrhea[19-22]. There is emerging evidence that probiotics may be useful in preventing or treating Clostridium difficile diarrhea and pouchitis[20,23,24]. Studies of probiotics for IBS have yielded contradictory results, which may be due to a variety of factors: small sample size; variability in trial design; heterogeneity of probiotic strain, dose and treatment duration; and patient characteristics. The wide availability of probiotics as non-prescription products and the lack of a synthesis of data regarding efficacy have prompted us to conduct this meta-analysis.

We conducted a systematic review of randomized, controlled trials published as full articles or meeting abstracts to: (1) assess the characteristics and quality of randomized clinical trials in this area and (2) synthesize data across studies regarding the efficacy of probiotics for IBS.

 

SEARCH STRATEGY

PubMed, Medline and Google Scholar were searched from 1982-2007 for articles unrestricted by language. Three on-line clinical trial registers were searched: Cochrane Central Register of Controlled Trials (www.cochrane.org), metaRegister of Controlled Trials (www.controlled-trials.com/mrct) and National Institutes of Health (www.clinicaltrials.gov). Secondary and hand searches of reference lists, other studies cross-indexed by authors, reviews, commentaries, books and meeting abstracts also were performed. Search terms included: irritable bowel syndrome, diarrhea, probiotics, risk factors, Rome criteria, Manning criteria, randomized controlled trials, placebo-controlled, bloating and associated author names. Search strategies were broad-based initially, then narrowed to the disease of interest to increase the search network[25]. The procedure for this meta-analysis was designed as suggested by Egger et al with clearly delineated parameters, a priori inclusion and exclusion criteria and standardized data extraction[26,27]. Abstracts of all citations and retrieved studies were reviewed and rated for inclusion. Full articles were retrieved if specific treatments were given for IBS. In some cases, only published abstracts from meetings were available. Published abstracts from meetings were included to lessen the potential for publication bias due to failure to publish negative findings.

 

INCLUSION AND EXCLUSION CRITERIA

The primary objective of this meta-analysis was to determine the overall efficacy of probiotics for IBS by comparing a common outcome in treated patients with a control group. Inclusion criteria included: randomized, controlled, blinded efficacy trials in humans published as full articles or meeting abstracts in peer-reviewed journals. Exclusion criteria included: pre-clinical studies, safety studies, case reports or case series, phase 1 studies in volunteers, reviews, duplicate reports, trials of unspecified treatments, uncontrolled studies, prebiotic treatments only (no living organisms) or insufficient data in article.

 

Assessment of methodological quality

Studies that met the inclusion criteria were graded for quality using the Linde Internal Validity Scale (LIVS), which includes the following six items: method of allocation to groups, concealment of allocation, baseline comparability of intervention and placebo groups, blinding of patients, blinding of evaluators, and intention to treat/handling of withdrawals and drop-outs[28-29]. If no information was provided for an item or it was unclear, authors were contacted for more information. If available information was still inadequate, then zero points were given for that item. Total possible scores range from 0 to 6.
All trials included in the meta-analysis had a total quality score of 3 or more and those with a score less than 3 were excluded. Two independent reviewers independently assessed inclusion criteria and quality of the trials. Inconsistencies were resolved by discussion.

 

Intent-to-treat (ITT) analysis

Studies were considered to have adhered to intention-to-treat principles if all subjects who were randomized were analyzed with the group to which they were originally assigned and if exclusions were primarily due to patient withdrawal or loss to follow-up. If the investigators excluded patients after randomization due to use of non-study medications or antibiotics, noncompliance with assigned treatment, or non-response to therapy, the analysis was not considered to be ITT.

 

Data extraction

Information on study design, methods, interventions, outcomes, adverse effects and treatments was extracted from each article using a standardized extraction table. When necessary, authors were contacted for data not reported in the original article.

 

Outcomes and definitions

We documented the types of outcomes for trials involving IBS and probiotic in the literature. Outcomes were reported by different studies as either the proportion of subjects reporting improvement or the change in symptom scores from baseline. We did not attempt to synthesize results from studies reporting changes in symptom scores because of numerous challenges including heterogeneity in scales and scoring systems across studies and inconsistent or incomplete reporting of numeric symptom scores. Thus, we selected the proportion of subjects with improvement in global IBS symptoms as the primary outcome for this meta-analysis. Secondary outcomes included the proportion of subjects with improvement in one of three common IBS symptoms: abdominal pain, bloating or flatulence. Documentation of the outcome was based on subject self-report and/or clinician assessment. 

 

Meta-analysis methods

To estimate pooled relative risks across studies, we first evaluated heterogeneity between and within trials using the c2 test[30]. The relative risks of responding to probiotic therapy were pooled using a random-effects model if significant heterogeneity was found or a fixed-effects model if the studies were homogenous[31]. The number needed to treat (NNT) was calculated using the reciprocal of the pooled absolute risk reduction. P values less than 0.05 were considered significant. Analyses were performed using Stata software version 9.2 (Stata Corporation, College Station, Texas).

 

Publication bias

We used a funnel scatterplot to assess the potential for publication bias[32]. Risk ratios were plotted against the standard error of the risk ratio (a surrogate for study size) of each study to detect asymmetry in the distribution of trials. Larger studies usually provide a more precise estimate of the true effect of the treatment and form the narrow spout of the funnel plot. Smaller trials provide less precise estimates, and the increased variability results in a wider cone of the funnel plot. A gap in the funnel plot (commonly, the absence of small studies with negative findings) suggests potential publication bias or methodological problems in smaller studies. Begg’s test was also used to assess potential publication bias[33,34].

 

Study characteristics predictive of positive findings

Because there was heterogeneity across studies, we examined study design characteristics that we hypothesized could be associated with results favoring probiotics over placebo. These analyses examined results for the primary outcome variable, reduction in global IBS symptoms. We classified studies as favoring probiotics if the unpooled RR was 0.67 or less. The study by Whorwell et al included 3 different probiotic dose arms but was considered as a single study for the purposes of this analysis[35]. Since one of the 3 arms showed results favoring probiotic, we classified this study as favoring probiotics. Characteristics examined as possible predictors included sample size, LIVS quality score, proportion of female subjects, probiotic dose, treatment duration, attrition > 20%, ITT analysis and use of a proprietary (commercial) vs nonproprietary product. To explore possible predictive variables, we first examined descriptive statistics (median and interquartile range for continuous variables, proportions for categorical variables). To test for statistical significance, we used the Wilcoxon rank-sum test for continuous data and Fisher’s exact test for categorical data.

 

Literature screening

The literature search yielded 3552 citations on probiotics, of which 789 addressed probiotics and IBS. Based on review of abstracts, 115 were selected for detailed screening.

 

Study Selection

The study selection process is shown in a QUOROM (Quality of Reporting of Meta-analysis) flow diagram (Figure 1)[27]. Overall, 95 studies that were screened failed to meet 1 or more of the inclusion criteria: 63 (66%) were reviews, 13 (14%) were pre-clinical studies, 6 (6%) had no control group[36-41], 3 (3%) were not randomized[42-44], and 10 (10%) were excluded for a variety of reasons. A total of 20 articles met inclusion criteria and provided data on 23 probiotic treatment arms for 1404 patients with IBS (Table 1)[17,35,45-62]. An additional seven trials were excluded after article retrieval and screening for issues related to quality and/or study design (Table 2)[63-68].

 

Study quality

The study quality of 23 treaments was assessed, and 20 trials with LIVS quality scores > 3.0 were included (Table 3).
The median quality score was 4 (range 3 to 6). Nine studies did not describe the method of randomization, 8 did not provide baseline comparison of groups, 14 did not specifically state that evaluators were blinded and 20 did not perform intention-to-treat analysis and/or did not fully describe withdrawals. For six studies, the published article or abstract did not contain sufficient information to allow quality scoring, requiring communication with the authors. Only three studies (15%) clearly documented their adherence to intention-to-treat principles[45,50,60].

There were a variety of ways in which studies failed to adhere to ITT principles. Seven studies excluded participants who used prohibited/non-study medications, including antibiotics, during the treatment phase[17,46,48,49,51,55,59], while five studies excluded subjects who demonstrated poor compliance with study medications[47,52,54,56,61]. Three studies reported that subjects either dropped out or were excluded due to inadequate response to treatment[49,58,62], while in 4 studies, subjects were excluded for worsening abdominal pain[51,52,54,56]. Often, it was unclear whether subjects with inadequate response or worsening symptoms were excluded at the investigators’ discretion or withdrew from the study of their own accord.

 

Description of included studies

A standardized data extraction table (Table 1) was used to characterize each clinical trial. Twenty randomized controlled trials provided adequate data regarding efficacy in a total of 1404 patients with IBS. In 20 trials, 23 probiotic treatment arms were compared to placebo control arms. Eighteen studies compared a single probiotic treatment arm to placebo, one study compared two probiotic treatments to placebo[17], and one study compared three doses of one probiotic against placebo[35]. The number of patients in each of these studies was generally small, with a median of 54 randomized subjects (range, 25-363; Figure 2). The daily dose of probiotic treatment ranged from 450 to 1 × 1012 colony-forming units (cfu)/day (median = 9 × 109). For the most part, the length of treatment in these studies was brief (median = 4 wk), with 90% of studies having a treatment phase of 8 wk or less.

 

Probiotic strain

Only two probiotics were tested in multiple trials: Lactobacillus rhamnosus GG in three trials[49,52,60] and Bifidobacterium infantis in two trials[17,35]. None of the L. rhamnosus GG trials provided evaluable data on either the primary or secondary outcomes, which prevented analysis by strain type.

 

Assessment and reporting of outcomes

The outcomes assessed and reported varied widely across the 20 studies. The effect on global IBS symptoms (measured as either proportion with symptom improvement or a reduction in severity scores) was reported in 15/20 (75%) of studies (Table 4) and was the primary outcome for 7 (35%) of studies. Effects on abdominal pain were reported by all studies. But, only 4 (20%) used this as a primary outcome measure[35,50,52,60].

Other symptoms were less consistently assessed (e.g. flatulence, 13/20 studies; mucus in stool, 3/20 studies; bloating, 15/20 studies). Only five studies collected some measure of quality of life[17,54,56,61,62]. Seven studies reported data for 3 or more symptoms or outcomes without specifying a primary outcome[17,46,48,49,53,54,56].

Some studies reported the number and proportion of subjects with improvement, while others reported change in numeric symptom scores since baseline. The scales used to measure the severity of IBS symptoms varied widely between studies, making it challenging to compare results across studies. Visual analogue scales were most often used, but still only used by 6 studies[17,46,48,51,55,57]. Likert scales were used by 3 studies[17,49,52], and specific validated scales were used by several studies Gastrointestinal Symptom Rating Scale (GSRS)[52,58] and IBS Severity Scoring System (IBS-SSS)[56,58,62]. Several studies used their own study-specific scale or scoring system[17,35,45,47,50,53,54,59-61]. Often it was unclear whether this scale had been validated.

While many studies assessed a wide range of IBS symptoms, few reported detailed results across the spectrum of symptoms (Table 4), making it more difficult to combine data across studies. For instance, only 8 of 13 studies reporting that they had collected data on flatulence provided this data in their paper and only 5 of 15 reporting they had collected data on stool frequency reported any such data in their paper.

 

Global responders

The primary outcome selected for this analysis was the proportion of patients in each group with global IBS symptoms by the end of treatment, with ‘responders’ being a dichotomous variable defined by study investigators (Table 5). Of the 23 treatment arms, 14 (61%) had evaluable data for this outcome. Eight treatment arms either did not collect data on global symptom relief[49,52,55,60] or reported change in symptom scores rather than proportion with improvement[17,53,56,57].

When the meta-analysis model was fitted, the c2 test for heterogeneity was 41.0 (P <0.001), indicating a high degree of heterogeneity; so a random-effects model was used to pool these results. The forest plot, weighted on sample size, is shown in Figure 3. Compared to placebo, probiotics were significantly protective (less global IBS symptoms compared to placebo at the end of the study) [pooled relative risk (RRpooled) = 0.77; 95% confidence interval (95% CI), 0.62-0.94]. The number needed to treat was 7.3. The funnel plot (Figure 4) is generally symmetrical, showing little evidence of publication bias. Begg’s test did not show statistically significant publication bias (z = 0.93, P = 0.35).

 

Sensitivity analyses

We repeated the meta-analysis weighting by study quality score rather than sample size, with similar results (RRpooled = 0.65; 95% CI, 0.52-0.82). As it appeared that the pooled risk estimate was heavily influenced by one large study[59], we re-ran the analysis excluding the study, but similar results were found (RRpooled = 0.82; 95% CI, 0.67-0.99).

 

Secondary outcomes

A priori secondary outcomes for this study included the proportion of subjects who reported one of three IBS symptoms: abdominal pain, bloating/distension, or flatulence (gas). Of 23 treatment arms, 12 (52%) had evaluable data on at least one of these secondary outcomes. Fourteen treatment arms either did not collect data on these secondary outcomes[45,47,51,58,61,62] or reported symptom scores rather than proportion with symptoms[17,53,56,57]. As only five treatment arms reported proportion of subjects with reduced bloating[46,49,52,54,55] and four reported proportion with improved flatulence[46,48,50,54], further statistical analyses were not performed for these outcomes.

Eight trials (11 probiotic treatment arms) had evaluable data for the proportion of patients reporting abdominal pain at the end of follow-up (Table 6)[35,46,48-50,52,54,59,60]. There was a high degree of heterogeneity (c2 = 36.6, P < 0.001), and so a random-effects model was used. The forest plot, weighted on sample size, is shown in Figure 5. Compared to placebo, probiotics were associated with less risk of abdominal pain (RRpooled = 0.78; 95% CI, 0.69-0.88). The number needed to treat was 8.9. The funnel plot was generally symmetrical, showing little evidence of publication bias, and Begg’s test did not show statistically significant publication bias (z = -0.70, P = 0.48). The pooled relative risk for abdominal pain was similar when weighted by study quality (RRpooled = 0.61; 95% CI, 0.45-0.81) and after exclusion of the two trials conducted in children (RRpooled = 0.77; 95% CI, 0.68-0.88)[52,60].

 

Study characteristics predicting positive results

We compared the characteristics of six studies that favored probiotics over placebo (study RR < 0.67 for improvement in global IBS symptoms)[35,46,48,50,54,59] with six studies showing a weak effect or no benefit[45,47,51,58,61,62]. Studies with a stronger probiotic effect were larger than those showing weak or no effect (median 80.5 subjects vs 50 subjects, P = 0.20) and had shorter duration of treatment (median 4 wk vs 6 wk, P = 0.60). but, these differences were not statistically significant. Two-thirds of studies showing strong protective effects used proprietary (commercial) products, compared to 100% of those showing weak or no effect (P = 0.46). In bivariate analyses, no characteristics differed significantly between the two types of studies.  

 

Adverse events

Most studies (17/20, 85%) provided only minimal information about adverse events. Fourteen studies (70%) stated that no serious adverse reactions were noted, but failed to provide any information on how adverse events were ascertained or what types of reactions were considered. Three (15%) of the trials did provide limited data on adverse reactions, including reactions such as “increased intestinal symptoms”, “epistaxis”, “aftertaste”, “anxiety” and “angina”, but did not report rates of adverse reactions by treatment group[17,49,54]. Three trials (15%) did not report any safety data[47,58,59].

We identified 20 clinical trials that met inclusion criteria and provided relevant information about the efficacy of probiotics for IBS symptoms. These trials included 23 probiotic treatment arms and 1404 subjects. Trials were generally small and of short duration and had moderate quality. But, the majority did not follow intention-to-treat principles. Overall, probiotic use was associated with less likelihood of global IBS symptoms compared to placebo (RR = 0.77; 95% CI, 0.62-0.94) and with abdominal pain by the end of follow-up (RR = 0.78; 95% CI, 0.69-0.88). There was not sufficient data to examine other individual IBS symptoms or the efficacy of individual probiotic strains.

 

Strengths and limitations

We performed a comprehensive review of the literature and made an effort to minimize publication bias by including recent studies as well as those published only as meeting abstracts. Validated quality scoring and data extraction were performed by two reviewers independently, using standardized templates, and differences were resolved by discussion. We excluded studies of poor quality, limiting the impact of serious study design flaws. We selected a primary outcome (global improvement in IBS symptoms) that is clinically relevant and of great concern to IBS patients, as is also true for our secondary outcome (relief of abdominal pain). Communication with study authors was a productive tool for obtaining data not reported in detail in some studies.

Our findings should be interpreted with caution due to important limitations of the existing literature. Two important limitations in the existing trials included the lack of ITT analysis and the presence of heterogeneity in both outcome assessment and study design. A crucial issue is the quality of included studies, with only 3 of 20 studies performing true intention-to-treat analyses. In many studies, participants were excluded from final analyses for reasons such as noncompliance, failure to respond to treatment, or use of prohibited medications. It is difficult to predict how these exclusions may have affected results. But, it is certainly possible that substantial bias could have been introduced, which could account for the apparent beneficial effects observed when data were pooled across studies. Missing values may cause both systematic and unpredictable bias in controlled trial results[69-71]. A recent meta-analysis of chondroitin for osteoarthritis found that small trials and those not analyzed according to ITT principles were more likely to report benefits from chondroitin, while larger studies with greater methodological rigor did not find an effect[72]. Larger studies utilizing ITT have not been performed to examine probiotics as potential therapy for IBS.

Heterogeneity was another important limitation of the published literature, including heterogeneity in the strain and dose of probiotic (which prevented analysis of effects of specific strains); sample size (smaller studies resulted in low power to detect effects in individual studies); duration of treatment and follow-up (short trials do not allow adequate follow-up given the chronic relapsing nature of IBS); and in the assessment and reporting of outcomes. All these sources of heterogeneity made it difficult to combine data from all twenty studies. Another important problem is the lack of systematic data collection and reporting about adverse effects. As a result, it is difficult to be sure that the probiotics studied have been adequately evaluated for safety.

 

Comparison with other systematic reviews

To date, no other meta-analysis of probiotics for IBS has been published. Recent published reviews of probiotics for IBS included fewer studies (range, 4 to 12) and focused primarily on evaluating the rationale and potential mechanisms for probiotics as treatment for IBS[9,13,73]. No prior reviews have attempted to calculate a pooled estimate of efficacy, and few reviews provided a detailed summary of individual studies’ outcome data or unpooled risk estimates.

 

Implications for future research

This review highlights important considerations for the design of future studies of probiotics as a potential treatment for IBS (Table 7). There is a need for standardized outcome assessments and larger studies, preferably with longer duration of treatment and follow-up. Future studies should make every effort to minimize loss-to-follow-up and to adhere to ITT principles, analyzing all subjects with the group to which they were originally assigned, notwithstanding potential noncompliance with treatment or the use of other (non-study) medications. Following these methodological principles will provide greater assurance that results are not due to bias. Future studies would benefit from better standardization of outcomes to be studied, including the use of uniform symptom scales. We recommend that future studies examine overall relief of IBS symptoms as an outcome. Although many prior studies primarily reported symptom scores, a statistically significant reduction in symptom score may not be meaningful to an individual patient suffering from IBS. Bijkerk et al examined the validity of 10 methods to assess IBS response and found a single question asking about ‘adequate relief of IBS-related symptoms’ was as valid as more detailed questionnaires on outcome[74]. In order to determine if one probiotic strain is more effective for IBS than others, confirmatory trials with the same probiotic strains are required.

Finally, it is important that future studies systematically assess potential adverse effects and provide detailed results, including rates of adverse effects in the treatment and placebo groups.

 

Implications for clinical practice

While our findings provide preliminary evidence that probiotics may be useful in treating IBS, it is too soon to recommend their use in clinical practice. The pooled relative risks reported here are based on studies with significant methodological limitations, and bias cannot be ruled out as the explanation for these positive findings. Since we did not find any evidence of significant adverse effects from these treatments, and given the lack of available conventional treatments, clinicians should strongly consider discussing the evidence of benefits and risks of probiotics with their patients with IBS. Although the costs of probiotics vary widely, the cost may be similar to other over-the-counter remedies for IBS (such as loperamide).

An important consideration is the lack of regulation of the commercial probiotic products that are currently available. No universal quality assurance programs exist to ensure that commercial products contain the probiotic strain and concentration that are claimed, or to ensure the absence of contamination that could pose risks to consumers. Some resources are available to provide further information about product testing; for example, ConsumerLab is an independent company in the U.S. that tests commercially available health and nutrition products and publishes data about the contents of various commercial products, including the presence of contaminants (http://www.consumerlab.com). They also offer a voluntary certification program. In the summer of 2007, the Food and Drug Administration issued new rules regarding good manufacturing practices for supplement manufacturers, aimed at ensuring more uniform quality of supplements. It remains to be seen whether these new rules will substantially improve the quality and safety of nutritional supplements.

 

CONCLUSION

In summary, the present meta-analysis suggests that probiotics offer promise for the treatment of IBS. Results should be interpreted cautiously given the methodological limitations of published studies. Future studies are needed, in particular larger studies of longer duration with greater methodological rigor. In addition, more data are needed regarding which specific strains and doses are most likely to be effective. The use of probiotics for IBS warrants further study, particularly given the chronic nature of this condition, its major impact on patients’ quality of life, and the dearth of other effective treatments.

 

ACKNOWLEDGMENTS

We would like to thank Dr. David Arterburn for his helpful feedback on this manuscript. The views expressed in this article are those of the authors and do not necessarily reflect the position or policy of the Department of Veterans Affairs.

 

REFERENCES

1      Cain KC, Headstrom P, Jarrett ME, Motzer SA, Park H, Burr RL, Surawicz CM, Heitkemper MM. Abdominal pain impacts
        quality of life in women with irritable bowel syndrome. Am J Gastroenterol 2006; 101: 124-132
   PubMed   DOI

2      Ford AC, Forman D, Bailey AG, Axon AT, Moayyedi P. Initial poor quality of life and new onset of dyspepsia: results from
        a longitudinal 10-year follow-up study. Gut 2007; 56: 321-327
   PubMed   DOI

3      Cremonini F, Talley NJ. Irritable bowel syndrome: epidemiology, natural history, health care seeking and emerging risk
        factors. Gastroenterol Clin North Am 2005; 34: 189-204
   PubMed   DOI

4      Saito YA, Cremonini F, Talley NJ. Association of the 1438G/A and 102T/C polymorphism of the 5-HT2A receptor gene
        with irritable bowel syndrome 5-HT2A gene polymorphism in irritable bowel syndrome. J Clin Gastroenterol 2005; 39:
        835; author reply 835-836
   PubMed   DOI

5      Spiller R, Aziz Q, Creed F, Emmanuel A, Houghton L, Hungin P, Jones R, Kumar D, Rubin G, Trudgill N, Whorwell P.
        Guidelines on the irritable bowel syndrome: mechanisms and practical management. Gut 2007; 56: 1770-1798

        PubMed   DOI

6      Ruigomez A, Garcia Rodriguez LA, Panes J. Risk of irritable bowel syndrome after an episode of bacterial
        gastroenteritis in general practice: influence of comorbidities. Clin Gastroenterol Hepatol 2007; 5: 465-469
   PubMed

        DOI

7      Agrawal A, Whorwell PJ. Irritable bowel syndrome: diagnosis and management. BMJ 2006; 332: 280-283   PubMed

        DOI

8      Cremonini F, Talley NJ. Treatments targeting putative mecha-nisms in irritable bowel syndrome. Nat Clin Pract
        Gastroenterol Hepatol 2005; 2: 82-88
   PubMed   DOI

9      Quigley EM, Flourie B. Probiotics and irritable bowel syndrome: a rationale for their use and an assessment of the
        evidence to date. Neurogastroenterol Motil 2007; 19: 166-172
   PubMed   DOI

10    Spiller RC. Role of infection in irritable bowel syndrome. J Gastroenterol 2007; 42 Suppl 17: 41-47   PubMed   DOI

11    Lin HC. Small intestinal bacterial overgrowth: a framework for understanding irritable bowel syndrome. JAMA 2004;
        292: 852-858
   PubMed   DOI

12    Malinen E, Rinttila T, Kajander K, Matto J, Kassinen A, Krogius L, Saarela M, Korpela R, Palva A. Analysis of the fecal
        microbiota of irritable bowel syndrome patients and healthy controls with real-time PCR. Am J Gastroenterol 2005; 100:
        373-382
   PubMed   DOI

13    Andresen V, Baumgart DC. Role of probiotics in the treatment of irritable bowel syndrome: potential mechanisms and
        current clinical evidence. Inter J Probiotics Prebiotics 2006; 1: 11-18
  

14    McFarland LV. Normal flora: diversity and functions. Microb Ecol Health Dis 2000; 12: 193-207   DOI

15    Elmer GW, McFarland LV, McFarland M. Introduction. Chapter 1. In: The Power of Probiotics: Improving Your Health
        with Beneficial Microbes., Binghamton, New York: Haworth Press, 2007: 3-5

16    McCarthy J, O’Mahony L, O’Callaghan L, Sheil B, Vaughan EE, Fitzsimons N, Fitzgibbon J, O’Sullivan GC, Kiely B, Collins
        JK, Shanahan F. Double blind, placebo controlled trial of two probiotic strains in interleukin 10 knockout mice and
        mechanistic link with cytokine balance. Gut 2003; 52: 975-980
   PubMed   DOI

17    O’Mahony L, McCarthy J, Kelly P, Hurley G, Luo F, Chen K, O’Sullivan GC, Kiely B, Collins JK, Shanahan F, Quigley EM.
        Lactobacillus and bifidobacterium in irritable bowel syndrome: symptom responses and relationship to cytokine profiles.
        Gastroenterology 2005; 128: 541-551
   PubMed   DOI

18    Verdu EF, Bercik P, Verma-Gandhu M, Huang XX, Blennerhassett P, Jackson W, Mao Y, Wang L, Rochat F, Collins SM.
        Specific probiotic therapy attenuates antibiotic induced visceral hypersensitivity in mice. Gut 2006; 55: 182-190

        PubMed   DOI

19    Szajewska H, Ruszczynski M, Radzikowski A. Probiotics in the prevention of antibiotic-associated diarrhea in children: a
        meta-analysis of randomized controlled trials. J Pediatr 2006; 149: 367-372
   PubMed   DOI

20    McFarland LV. Meta-analysis of probiotics for the prevention of antibiotic associated diarrhea and the treatment of
        Clostridium difficile disease. Am J Gastroenterol 2006; 101: 812-822
   PubMed   DOI

21    McFarland LV, Elmer GW and McFarland M. Meta-analysis of Probiotics for the Prevention and Treatment of Acute
        Pediatric Diarrhea. Internl J Probiotics Prebiotics 2006; 1: 63-76
    

22    McFarland LV. Meta-analysis of probiotics for the prevention of traveler’s diarrhea. Travel Med Infect Dis 2007; 5: 97-
        105
   PubMed   DOI

23    Kuhbacher T, Ott SJ, Helwig U, Mimura T, Rizzello F, Kleessen B, Gionchetti P, Blaut M, Campieri M, Folsch UR, Kamm
        MA, Schreiber S. Bacterial and fungal microbiota in relation to probiotic therapy (VSL#3) in pouchitis. Gut 2006; 55:
        833-841
   PubMed   DOI

24    Mimura T, Rizzello F, Helwig U, Poggioli G, Schreiber S, Talbot IC, Nicholls RJ, Gionchetti P, Campieri M, Kamm MA.
        Once daily high dose probiotic therapy (VSL#3) for maintaining remission in recurrent or refractory pouchitis. Gut 2004;
        53: 108-114
   PubMed   DOI

25    Shaw RL, Booth A, Sutton AJ, Miller T, Smith JA, Young B, Jones DR, Dixon-Woods M. Finding qualitative research: an
        evaluation of search strategies. BMC Med Res Methodol 2004; 4: 5
   PubMed   DOI

26    Egger M, Smith GD, Phillips AN. Meta-analysis: principles and procedures. BMJ 1997; 315: 1533-1537   PubMed  

27    Moher D, Cook DJ, Eastwood S, Olkin I, Rennie D, Stroup DF. Improving the quality of reports of meta-analyses of
        randomised controlled trials: the QUOROM statement. QUOROM Group. Br J Surg 2000; 87: 1448-1454
   PubMed   DOI

28    Lim B, Manheimer E, Lao L, Ziea E, Wisniewski J, Liu J, Berman B. Acupuncture for treatment of irritable bowel
        syndrome. Cochrane Database Syst Rev 2006; CD005111
   PubMed  

29    Linde K, Ramirez G, Mulrow CD, Pauls A, Weidenhammer W, Melchart D. St John’s wort for depression--an overview
        and meta-analysis of randomised clinical trials. BMJ 1996; 313: 253-258
   PubMed  

30    Clarke M, Oxman AD, eds. Analyzing and Presenting Results: Cochrane Reviewers’ Handbook 4.2 (updated November
        2002- Section 8.) In: the Cochrane Library. Oxford: Update Software; 2003, issue 1, cited January 23, 2008. Available
        from: URL: http://www.cochrane.org/ resources/handbook/index.htm

31    DerSimonian R, Laird N. Meta-analysis in clinical trials. Control Clin Trials 1986; 7: 177-188   PubMed   DOI

32    Egger M, Davey Smith G, Schneider M, Minder C. Bias in meta-analysis detected by a simple, graphical test. BMJ 1997;
        315: 629-634
   PubMed  

33    Begg CB, Mazumdar M. Operating characteristics of a rank correlation test for publication bias. Biometrics 1994; 50:
        1088-1101
   PubMed   DOI

34    Sutton AJ, Duval SJ, Tweedie RL, Abrams KR, Jones DR. Empirical assessment of effect of publication bias on meta-
        analyses. BMJ 2000; 320: 1574-1577
   PubMed   DOI

35    Whorwell PJ, Altringer L, Morel J, Bond Y, Charbonneau D, O’Mahony L, Kiely B, Shanahan F, Quigley EM. Efficacy of an
        encapsulated probiotic Bifidobacterium infantis 35624 in women with irritable bowel syndrome. Am J Gastroenterol
        2006; 101: 1581-1590
   PubMed   DOI

36    Adler SN. The probiotic agent Escherichia coli M-17 has a healing effect in patients with IBS with proximal inflammation
        of the small bowel. Dig Liver Dis 2006; 38: 713
   PubMed   DOI

37    Bazzocchi G, Gionchetti P, Almerigi PF, Amadini C, Campieri M. Intestinal microflora and oral bacteriotherapy in irritable
        bowel syndrome. Dig Liver Dis 2002; 34 Suppl 2: S48-S53
   PubMed   DOI

38    Brigidi P, Vitali B, Swennen E, Bazzocchi G, Matteuzzi D. Effects of probiotic administration upon the composition and
        enzymatic activity of human fecal microbiota in patients with irritable bowel syndrome or functional diarrhea. Res
        Microbiol 2001; 152: 735-741
   PubMed   DOI

39    Colecchia A, Vestito A, La Rocca A, Pasqui F, Nikiforaki A, Festi D. Effect of a symbiotic preparation on the clinical
        manifestations of irritable bowel syndrome, constipation-variant. Results of an open, uncontrolled multicenter study.
        Minerva Gastroenterol Dietol 2006; 52: 349-358
   PubMed  

40    Drisko J, Bischoff B, Hall M, McCallum R. Treating irritable bowel syndrome with a food elimination diet followed by food
        challenge and probiotics. J Am Coll Nutr 2006; 25: 514-522
   PubMed  

41    Fan YJ, Chen SJ, Yu YC, Si JM, Liu B. A probiotic treatment containing Lactobacillus, Bifidobacterium and Enterococcus
        improves IBS symptoms in an open label trial. J Zhejiang Univ Sci B 2006; 7: 987-991
   PubMed   DOI

42    Astegiano M, Pellicano R, Terzi E, Simondi D, Rizzetto M. Treatment of irritable bowel syndrome. A case control
        experience. Minerva Gastroenterol Dietol 2006; 52: 359-363
   PubMed  

43    Tsuchiya J, Barreto R, Okura R, Kawakita S, Fesce E, Marotta F. Single-blind follow-up study on the effectiveness of a
        symbiotic preparation in irritable bowel syndrome. Chin J Dig Dis 2004; 5: 169-174
   PubMed   DOI

44    Sen S, Mullan MM, Parker TJ, Woolner JT, Tarry SA, Hunter JO. Effect of Lactobacillus plantarum 299v on colonic
        fermentation and symptoms of irritable bowel syndrome. Dig Dis Sci 2002; 47: 2615-2620
   PubMed   DOI

45    Maupas JL, Champemont P, Delforge M. Treatment of irritable bowel syndrome. Double blind trial of Saccharomyces
        boulardii. Medecine Chirurgie Digestives 1983; 12: 77-79
    

46    Gade J, Thorn P. Paraghurt for patients with irritable bowel syndrome. A controlled clinical investigation from general
        practice. Scand J Prim Health Care 1989; 7: 23-26
   PubMed   DOI

47    Halpern GM, Prindiville T, Blankenburg M, Hsia T, Gershwin ME. Treatment of irritable bowel syndrome with Lacteol
        Fort: a randomized, double-blind, cross-over trial. Am J Gastroenterol 1996; 91: 1579-1585
   PubMed  

48    Nobaek S, Johansson ML, Molin G, Ahrne S, Jeppsson B. Alteration of intestinal microflora is associated with reduction in
        abdominal bloating and pain in patients with irritable bowel syndrome. Am J Gastroenterol 2000; 95: 1231-1238

        PubMed   DOI

49    O’Sullivan MA, O’Morain CA. Bacterial supplementation in the irritable bowel syndrome. A randomised double-blind
        placebo-controlled crossover study. Dig Liver Dis 2000; 32: 294-301
   PubMed   DOI

50    Niedzielin K, Kordecki H, Birkenfeld B. A controlled, double-blind, randomized study on the efficacy of Lactobacillus
        plantarum 299V in patients with irritable bowel syndrome. Eur J Gastroenterol Hepatol 2001; 13: 1143-1147
   PubMed

        DOI

51    Kim HJ, Camilleri M, McKinzie S, Lempke MB, Burton DD, Thomforde GM, Zinsmeister AR. A randomized controlled trial
        of a probiotic, VSL#3, on gut transit and symptoms in diarrhoea-predominant irritable bowel syndrome. Aliment
        Pharmacol Ther 2003; 17: 895-904
   PubMed   DOI

52    Bausserman M, Michail S. The use of Lactobacillus GG in irritable bowel syndrome in children: a double-blind
        randomized control trial. J Pediatr 2005; 147: 197-201
   PubMed   DOI

53    Bittner AC, Croffut RM, Stranahan MC. Prescript-Assist probiotic-prebiotic treatment for irritable bowel syndrome: a
        methodologically oriented, 2-week, randomized, placebo-controlled, double-blind clinical study. Clin Ther 2005; 27: 755-
        761
   PubMed   DOI

54    Kajander K, Hatakka K, Poussa T, Farkkila M, Korpela R. A probiotic mixture alleviates symptoms in irritable bowel
        syndrome patients: a controlled 6-month intervention. Aliment Pharmacol Ther 2005; 22: 387-394
   PubMed   DOI

55    Kim HJ, Vazquez Roque MI, Camilleri M, Stephens D, Burton DD, Baxter K, Thomforde G, Zinsmeister AR. A randomized
        controlled trial of a probiotic combination VSL# 3 and placebo in irritable bowel syndrome with bloating.
        Neurogastroenterol Motil 2005; 17: 687-696
   PubMed   DOI

56    Niv E, Naftali T, Hallak R, Vaisman N. The efficacy of Lactobacillus reuteri ATCC 55730 in the treatment of patients with
        irritable bowel syndrome--a double blind, placebo-controlled, randomized study. Clin Nutr 2005; 24: 925-931
   PubMed

        DOI

57    Kim YG, Moon JT, Lee KM, Chon NR, Park H. The effects of probiotics on symptoms of irritable bowel syndrome. Korean
        J Gastroenterol 2006; 47: 413-419
   PubMed  

58    Simren M, Syrous A, Lindh A, Abrahamsson H. Effects of lactobacillus plantarum 299v on symptoms and rectal sensitivity
        in patients with irritable bowel syndrome (IBS) - A randomized, double-blind controlled trial. Gastroenterology 2006;
        130 Suppl 2: A600
    

59    Enck P, Menke G, Zimmermann K, Martens U, Klosterhalfen S. Effective probiotic therapy of the irritable bowel syndrome
        (IBS): A multi-center clinical trial with primary care physicians. Gastroenterology 2007; 132 Suppl 2: A79

60    Gawronska A, Dziechciarz P, Horvath A, Szajewska H. A randomized double-blind placebo-controlled trial of
        Lactobacillus GG for abdominal pain disorders in children. Aliment Pharmacol Ther 2007; 25: 177-184
   PubMed  

61    D'haens GR, Kovacs G, Vergauwe P, Lonovics J, Bouhnik Y, Weiss W, Brunner H, Lavergne-Slove A, Di Stefano AF,
        Marteau P. A randomized controlled trial of the probiotic combination Lactibiane (R) in irritable bowel syndrome, the
        Lactibiane (R) study group. Gastroenterology 2007; 132 Suppl 2: A371

62    Simren M, Lindh A, Sammelsson L, Olsson J, Posserud I, Strid H, Abrahamsson H. Effect of yoghurt containing three
        probiotic bacteria in patients with irritable bowel syndrome (IBS) - A randomized, double-blind, controlled trial.
        Gastroenterology 2007; 132 Suppl 2: A210

63    DiBaise JK, Lof J, Taylor K, Quigley EM. Lactobacillus plantarum 299V in the irritable bowel syndrome: A randomized,
        double-blind, placebo-controlled crossover study. Gastroenterology 2000; 118 Suppl 2: A3163

64    Saggioro A. Probiotics in the treatment of irritable bowel syndrome. J Clin Gastroenterol 2004; 38: S104-S106 

        PubMed   DOI

65    Long ZR, Yu CH, Yang Y, Wang HN, Chi XX. Clinical observation on acupuncture combined with microorganism
        pharmaceutical preparations for treatment of irritable bowel syndrome of constipation type. Zhongguo Zhenjiu 2006; 26:
        403-405
   PubMed  

66    Kajander K, Korpela R. Clinical studies on alleviating the symptoms of irritable bowel syndrome. Asia Pac J Clin Nutr
        2006; 15: 576-580
   PubMed  

67    Bittner AC, Croffut RM, Stranahan MC, Yokelson TN. Prescript-assist probiotic-prebiotic treatment for irritable bowel
        syndrome: an open-label, partially controlled, 1-year extension of a previously published controlled clinical trial. Clin
        Ther 2007; 29: 1153-1160
   PubMed   DOI

68    Moon JT, Kim HS, Park HJ. Effects of probiotics on the intestinal gas volume score and symptoms in patients with
        irritable bowel syndrome. A randomized double-blind placebo-controlled study. Gastroenterology 2007; 132 Suppl 2:
        A688

69    Porta N, Bonet C, Cobo E. Discordance between reported intention-to-treat and per protocol analyses. J Clin Epidemiol
        2007; 60: 663-669
   PubMed   DOI

70    Salim A, Mackinnon A, Griffiths K. Sensitivity analysis of intention-to-treat estimates when withdrawals are related to
        unobserved compliance status. Stat Med 2008; 27: 1164-1179
   PubMed   DOI

71    Brittain E, Lin D. A comparison of intent-to-treat and per-protocol results in antibiotic non-inferiority trials. Stat Med
        2005; 24: 1-10
   PubMed   DOI

72    Reichenbach S, Sterchi R, Scherer M, Trelle S, Burgi E, Burgi U, Dieppe PA, Juni P. Meta-analysis: chondroitin for
        osteoarthritis of the knee or hip. Ann Intern Med 2007; 146: 580-590
   PubMed  

73    Camilleri M. Probiotics and irritable bowel syndrome: rationale, putative mechanisms, and evidence of clinical efficacy. J
        Clin Gastroenterol 2006; 40: 264-269
   PubMed   DOI

74    Bijkerk CJ, de Wit NJ, Muris JW, Jones RH, Knottnerus JA, Hoes AW. Outcome measures in irritable bowel syndrome:
        comparison of psychometric and methodological characteristics. Am J Gastroenterol 2003; 98: 122-127
   PubMed   DOI

 

S- Editor  Zhong XY    L- Editor  Alpini G    E- Editor  Ma WH

 

 

 

 

Reviews Add
more>>


Related Articles:
Synthesis of an enzyme-dependent prodrug and evaluation of its potential for colon targeting
Non-invasive investigation of inflammatory bowel disease
Fertility and pregnancy in inflammatory bowel disease
Prevalence, predictors, and clinical consequences of medical adherence in IBD: How to improve it?
Soluble intercellular adhesion molecule-1, D-lactate and diamine oxidase in patients with inflammatory bowel disease
more>>