The safety profile of probiotic VSL#3®. A meta-analysis of safety data from double-blind, randomized, placebo-controlled clinical trials

OBJECTIVE: A high-concentration of a multi-strain probiotic mixture, VSL#3® is widely used ‘whenever it is useful to promote the balance of intestinal flora’. As a food supplement, VSL#3® has been so far scarcely investigated on the aspect of safety. To fill this gap, in this paper, we analyzed the adverse events (AEs) recorded during the conduct of three (3) double-blind, randomized, placebo-controlled trials carried out to explore the efficacy of VSL#3® in various clinical settings. Data from a large open-label observational trial were also considered. MATERIALS AND METHODS: All trials included in the analysis were carried out according to good clinical practice (GCP) rules. AEs were classified by System Organ Class (SOC), Preferred Term (PT) and frequency. Differences vs. placebo control were considered as statistically significant if the p-value was < 0.05. RESULTS: A total of 120 patients were analyzed, 70 patients being included in the randomized controlled trials. In this population, 45 patients had at least one AE, 20 (64.5%) in the placebo group and 25 (64.1%) in the VSL#3® group. 29 patients had at least one related AE, 14 (45.2%) and 15 (38.5%) in the two treatment groups, respectively. Only one AE was assessed as serious, i.e., Foetal malformation, which occurred in the placebo group and was considered unrelated. No significant difference was found between VSL#3® and placebo for any of the SOC considered, with the exception of Injury, poisoning and procedural complications, which was in favor of VSL#3®. CONCLUSIONS: Based on GCP-quality data from clinical trials, we conclude that VSL#3® is a safe and well-tolerated agent.