Several systematic reviews have been conducted [71-76], most of which (although using different sets of primary studies) reached similar conclusions. One of the most recent meta-analyses (34 placebo-controlled trials) concluded that [71]:
Probiotics were associated with a significant 52 percent reduction in antibiotic-associated diarrhea (95% CI 35 to 65 percent).
Probiotics were associated with an 8 percent reduction in traveler's diarrhea (95% CI -6 to 21 percent).
Probiotics were associated with a 57 percent reduction in risk of acute diarrhea of various causes in children (95% CI 37 to 51 percent) and a 26 percent reduction in adults (95% CI 7 to 49 percent).
The protective effects did not vary significantly among the probiotics strains Saccharomyces boulardii, Lactobacillus rhamnosus GG, Lactobacillus acidophilus, Lactobacillus bulgaricus and other strains used alone or in combination of two or more strains.
A later meta-analysis that focused on studies of children found a protective effect of probiotics on antibiotic-associated diarrhea on per-protocol analysis, but results were not significant on intention-to-treat analysis [75].
In a subsequent randomized trial, 255 patients were assigned to one of three regimens using Lactobacillus acidophilus and L. casei or placebo: (A) two probiotic capsules daily, (B) one probiotic and one placebo capsule daily, or (C) two placebo capsules daily [77]. Patients receiving probiotic capsules had lower rates of antibiotic-associated diarrhea than patients receiving placebo (16 percent in group A, 28 percent in group B, and 44 percent in group C). In addition, the mean duration of antibiotic-associated diarrhea was shorter in those receiving probiotics (3 days for group A, 4 days for group B, and 6 days for group C).
In summary, systematic reviews suggest that probiotics (including various bacterial species and the yeast S. boulardii) are effective in reducing the incidence of diarrhea in patients who are taking antibiotics. However, discordant data have been published and there is little detailed information regarding the optimal dose or timing of supplementation or the effects on subgroups of patients. A more recent, larger randomized trial suggests that there is a role for probiotics for the prevention of antibiotic-associated diarrhea. It also suggests that probiotics may shorten the period of diarrhea in patients who have already developed it.
