Probiotics Do Not Prevent Antibiotic-Associated Diarrhea

A new study shows that Saccharomyces boulardii is ineffective in reducing the occurrence of antibiotic-associated diarrhea (AAD) or Clostridium difficile-associated diarrhea (CDAD) in hospitalized patients.

Researchers at Alessandro Manzoni Hospital (Lecco, Italy) conducted a single-center, randomized, double-blind, placebo-controlled trial involving 562 consecutive eligible patients (mean age 79 years) who were being prescribed antibiotics or on antibiotic therapy. Exclusion criteria were ongoing diarrhea, recent assumption of probiotics, lack of informed consent, inability to ingest capsules, and severe pancreatitis. Patients received a capsule containing S. boulardii or placebo twice daily within 48 hours of beginning antibiotic therapy, continued treatment for 7 days after antibiotic withdrawal, and were followed for 12 weeks after ending antibiotic treatment.

The results showed that a total of 275 patients were randomized to the study, while 204 (98 on placebo) completed the follow-up. AAD developed in 13.3% of the patients receiving placebo and in 15.1% of those receiving S. boulardii. Five cases of CDAD occurred, two in the placebo group (2.0%) and three in the probiotic group (2.8%). There was no difference in mortality rates (12.7% versus 15.6%). The study was published in the June 2012 issue of the American Journal of Gastroenterology.


“In clinical trials, the administration of S. boulardii has been associated both with an overall 53% relative reduction of the risk of developing AAD and a reduction in CDAD recurrence. However, several methodological drawbacks affected most clinical studies that have investigated the possible prophylactic action of probiotics against AAD and CDAD,” concluded lead author Pietro Pozzoni, MD, “including a limited or noncalculated sample size, inadequate study power, lack of generalizability of the results due to manner of the selection of the enrolled patients, and unspecified information about the application of nonpharmacological infection control measures.”

Probiotic organisms are live microorganisms which when administered in adequate amounts confer a health benefit on the host. Lactic acid bacteria (LAB) and bifidobacteria are the most common types of microbes used as probiotics; but certain yeasts and bacilli may also be used. Probiotics are commonly consumed as part of fermented foods with specially added active live cultures, such as in yogurt, soy yogurt, or as dietary supplements. Probiotics are also delivered in fecal transplants, in which stool from a healthy donor is delivered like a suppository to an infected patient.

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Alessandro Manzoni Hospital