AIM: To summarize the evidence from randomized controlled trials (RCTs) regarding the effect of probiotics by using a meta-analytic approach.

METHODS: In July 2013, we searched PubMed, EMBASE, Ovid, the Cochrane Library, and three Chinese databases (Chinese Biomedical Literature Database, Chinese Medical Current Content, and Chinese Scientific Journals database) to identify relevant RCTs. We included RCTs investigating the effect of a combination of probiotics and standard therapy (probiotics group) with standard therapy alone (control group). Risk ratios (RRs) were used to measure the effect of probiotics plus standard therapy on Helicobacter pylori (H. pylori) eradication rates, adverse events, and patient compliance using a random-effect model.

RESULTS: We included data on 6997 participants from 45 RCTs, the overall eradication rates of the probiotic group and the control group were 82.31% and 72.08%, respectively. We noted that the use of probiotics plus standard therapy was associated with an increased eradication rate by per-protocol set analysis (RR = 1.11; 95%CI: 1.08-1.15; P < 0.001) or intention-to-treat analysis (RR = 1.13; 95%CI: 1.10-1.16; P < 0.001). Furthermore, the incidence of adverse events was 21.44% in the probiotics group and 36.27% in the control group, and it was found that the probiotics plus standard therapy significantly reduced the risk of adverse events (RR = 0.59; 95%CI: 0.48-0.71; P < 0.001), which demonstrated a favorable effect of probiotics in reducing adverse events associated with H. pylori eradication therapy. The specific reduction in adverse events ranged from 30% to 59%, and this reduction was statistically significant. Finally, probiotics plus standard therapy had little or no effect on patient compliance (RR = 0.98; 95%CI: 0.68-1.39; P = 0.889).

CONCLUSION: The use of probiotics plus standard therapy was associated with an increase in the H. pylori eradication rate, and a reduction in adverse events resulting from treatment in the general population. However, this therapy did not improve patient compliance.

Since its identification in 1982 by Barry Marshall and Robin Warren, Helicobacter pylori (H. pylori) has been studied for more than 30 years. The infection rate of this single dominant pathogen in the stomach varies between 1.2% and 95% according to age, geographic area, socioeconomic status, and other factors[1-5]. Infection with this organism results in a chronic effect by causing duodenal or gastric ulcers[6,7], gastric cancer[8,9], and gastric mucosa-associated lymphoid-tissue lymphoma[6,10]. The therapy used for the eradication of H. pylori also prevents the development of the diseases mentioned above in patients who are at high risk[8,11-13]. The success rate of standard therapy ranges from 60% to 90% using first-line treatment, and around 70% with second-line treatment[14-16]. Furthermore, the disruption of coevolved human and H. pylori genomes might play an important role in the high incidence of gastric disease[17,18]. Hence, the development of improved strategies is still under investigation to increase the efficiency of eradication or to increase patient compliance, which may contribute to a greater clinical value because of the prevalence of H. pylori infection in large populations[19]. Probiotics have a positive effect on H. pylori eradication since these compounds also induce anti-inflammatory and anti-oxidative mechanisms that regulate intestinal microbiota[20-23].

Although several meta-analyses[24-27] have assessed the efficacy and safety of probiotics plus standard therapy, most of these studies have investigated these effects with respect to specific strains or certain formulations of probiotics[24-26]. Tong et al[27] demonstrated that the administration of probiotics can both improve the eradication rate and reduce adverse events, but their study did not examine the effect of probiotics on patient compliance. The benefits of probiotics supplementation in the treatment of antibiotic resistant H. pylori are still unclear due to the lack of supporting evidence[28]. In this study, we performed a meta-analysis of available randomized controlled trials (RCTs) to evaluate the effect of probiotics on H. pylori eradication, adverse events, and patient compliance.

Based on the literature search strategy, 4531 titles and abstracts were found from the 4 English databases; 102 of them were further searched based on abstracts or full articles, and 38 studies were enrolled. Another 7 studies from Chinese databases were enrolled later. Finally, 45 articles with 6997 participants were included[39-83] (PRISMA Flowchart). The characteristics of the 45 studies are listed in Table 1.

We acquired data relating to 6601 individuals to assess the effect of probiotics plus standard therapy on eradication rates. The pooled eradication rates for the probiotics group and the control group by PPS analysis were 86.23% and 76.60%, respectively. Overall, probiotics plus standard therapy significantly increased the eradication rates (RR = 1.11; 95%CI: 1.08-1.15; P < 0.001; Figure 1). Similarly, in ITT analysis, the pooled eradication rates for the probiotics group and the control group were 82.31% and 72.08%, respectively. Probiotics plus standard therapy significantly increased the eradication rates (RR = 1.13; 95%CI: 1.10-1.16; P < 0.001; Figure 2). Although there was significant heterogeneity across the trials by PPS analysis, a sensitivity analysis was conducted and the results suggested that the data were not affected by the sequential exclusion of any particular trial from the pooled analysis.

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Figure 1 Effects of probiotics plus standard therapy on eradication rate by per-protocol set analysis compared with standard therapy alone. CI: Confidence interval.

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Figure 2 Effects of probiotics plus standard therapy on eradication rate by intention-to-treat analysis compared with standard therapy alone.

We acquired data on 5312 individuals to assess the effect of probiotics plus standard therapy on adverse events, and reported 1499 adverse events. We noted that probiotics plus standard therapy significantly reduced the risk of adverse events (RR = 0.59; 95%CI: 0.48-0.71; P < 0.001; Figure 3). Substantial heterogeneity was observed in the magnitude of the effect across the trials (I² = 81.6%; P < 0.001). However, following sequential exclusion of each trial from the pooled analysis, we found that the outcome was not affected by the exclusion of any specific trial. The incidence rates were 21.44% and 36.27% in the probiotics group and the control group, respectively, which demonstrated a favorable effect of probiotics on the reduction of adverse events during H. pylori eradication therapy. As presented in Table 2, the combined effects of probiotics were statistically significant for all the listed adverse events, which clarified the protective effects of probiotics against these adverse events.

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Figure 3 Effects of probiotics plus standard therapy on total adverse events compared with standard therapy alone.

We acquired data on 4033 individuals to assess the effect of probiotics plus standard therapy on compliance, and reported 132 events of non-compliance. The inclusion of probiotics in the H. pylori eradication treatment regimen did not improve patient compliance according to the results of the pooled analysis (RR = 0.98; 95%CI: 0.68-1.39; P = 0.889; without evidence of heterogeneity; Figure 4).

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Figure 4 Effects of probiotics plus standard therapy on patients compliance compared with standard therapy alone.

The studies were divided into subgroups based on the age of the patients, single or multiple probiotic strains, dosage of probiotics, duration of probiotics intake, duration of standard eradication therapy, duration between the end of the therapy and assessment, probiotic strains and types of eradication therapy (Table 3). Overall, we noted that Clostridium had no significant effect on the eradication rate, and furthermore, probiotics did not affect the eradication rate if patients received a second-line standard therapy. Subgroup analyses based on other factors were associated with a statistically significant increase in the eradication rate.

A review of funnel plots did not exclude the potential for publication bias for the eradication rate, adverse events, and patient compliance. The Egger test[37] results showed potential publication bias for the eradication rate, adverse events, and patient compliance. The Begg test[38] results showed potential publication bias for patient compliance. The conclusions did not change after adjustment for publication bias by using the trim and fill method[84].

Through systematic review and meta-analysis using the results from 45 studies as solid supporting evidence, the effectiveness of the use of probiotics in H. pylori eradication therapy is based on 3 criteria: eradication rate, adverse events, and patient compliance. Our results suggest that additional probiotic supplementation significantly increases the eradication rate, and reduces adverse events. However, there is no significant effect on patient compliance.

The eradication rate of H. pylori using standard therapy plus probiotics has been significantly improved by about 13% compared with standard therapy alone. The value of RR is small because both the probiotics group and the control group have a relatively large eradication rate. Therefore, an improved eradication rate is the best indicator of the effectiveness of probiotics supplementation. Hence, the addition of probiotics to standard H. pylori eradication therapy improves the H. pylori eradication success rate within a population.

The duration of antibiotic treatment, different regimens of standard therapy, patient age, dosage of probiotics, different strains of probiotics[4,40,85-87], and different types of standard therapy have been reported to potentially influence the eradication outcome. In our study, there was a statistically significant increase in eradication rates in nearly all the subgroups when these factors were also taken into consideration. These subgroups showed similar outcomes with strong statistical significance, which may be influenced by a large sample size. We consider that probiotics had a comparable effect on the H. pylori eradication rate in all these subgroups of more than 500 patients. More studies are needed to assess the outcome in groups with fewer patients, such as groups of children and patients who received second-line therapy.

In addition to the subgroups mentioned above, antibiotic resistance can create a significant problem in H. pylori eradication therapy because it can become a major cause of initial eradication failure[19,88-90]. The prevalence of clarithromycin resistance cases treated with clarithromycin-containing triple therapy was reported to be 10%-30%[19,91]. With an increasing number of patients infected with clarithromycin and/or fluoroquinolone resistant H. pylori[92], quadruple therapy with bismuth colloid or sequential therapy has been suggested[92,93]. Probiotic supplementation in this population has rarely been studied before. In this meta-analysis, the studies focusing on antibiotic resistant H. pylori were far fewer than expected. Therefore, we have not included a thorough discussion on the topic of antibiotic-resistant strains here. The results from studies conducted so far seem promising and worth pursuing further through the initiation of studies using a larger population of patients.

In addition to improving the eradication rate of infectious organisms, the administration of probiotics can also reduce the incidence of adverse events by preventing or reducing pathogenic adherence, inducing the production of stomach acid, hydrogen peroxide, and bacteriocins to antagonize pathogen growth, and encourage the formation of normal balanced flora[68]. In our study, all the reported adverse events had RRs < 1, which indicated that the use of probiotics effectively protected the gut flora during H. pylori eradication. The overall incidence of adverse events was reduced by approximately 41% in the probiotics group. There are also studies confirming that the administration of probiotics can prevent diarrhea[94], abdominal bloating[95], and constipation[96-98].

Since probiotics are effective in the prevention of adverse events, they were also expected to promote patient compliance[22,28]. Non-compliance may drastically affect the H. pylori eradication success rate[2]; this aspect has seldom been studied. Manfredi et al[48] reported that the improvement in patient compliance in a study administering lactoferrin and probiotics to treat H. pylori infection was not statistically significant. Most studies had no dropouts or minimal losses to follow-up. The non-compliance rate was low and may relate to intrinsic personality traits, which can only be studied using a meta-analysis approach. Unexpectedly, there was no evidence showing a lower rate of non-compliance in the probiotics group. The RR showed a slight tendency for improved patient compliance, but this did not have any practical benefit on eradication success.

In clinical practice, the overall benefit of administering prophylactic probiotics to H. pylori-infected patients is not only related to the eradication success or reduced adverse events, but also to medical expenses; the influence of the latter factor in H. pylori eradication is still unclear. As H. pylori infection is more prevalent in developing countries or areas of lower socioeconomic status[4,99], the cost-effectiveness of taking probiotics may be subtle and difficult to evaluate. Tursi et al[77] reported that the extra cost of probiotics may be a limiting factor preventing widespread use. Some researchers report that probiotics were economical[100], but more evidence is required to support this statement.

This study may have the following limitations: (1) some publications may have been neglected to be added to the study because they were not included in any of the databases that were searched, leading to publication bias. Some publications that were unavailable were requested from the corresponding author in order to include their data in this study but only a few requests were answered; (2) there is a limited number of papers that include some subgroups, such as patients infected with antibiotic resistant H. pylori who were treated with probiotics. Analysis of these subgroups was not conducted; (3) there may be bias introduced by including studies with multiple arms, and routine means of measuring heterogeneity and publication bias; and (4) probiotics were analyzed by strains instead of by preparations that are available in clinical practice. Furthermore, the eradication therapies were divided into first-line or second-line therapies instead of into specific regimens to account for study number limitations. The correlation of probiotics and standard therapy was not included, and may contribute important information to this study.

In conclusion, the use of probiotics to supplement standard therapy in patients infected with H. pylori increased the eradication rate of the organism by about 13% and decreased the overall rate of adverse events by approximately 41%, independent of patient age, genera or dosage of probiotics, time of standard therapy or assessment, and therapy regimen. Unexpectedly, the patient compliance rate did not improve with the addition of probiotics to the therapeutic regimen. An economic evaluation is required to establish the cost-effectiveness of the addition of probiotics to H. pylori eradication therapy, and to determine whether the combination of probiotics with a standard therapy would be beneficial in clinical practice.