PARIS — A daily dose of probiotics failed to ward off diarrhea caused by antibiotics in a study of thousands of elderly patients that may deal a blow to the industry.
The study of 2,941 patients found little difference between the group of hospitalized people who, in addition to a course of antibiotics, were given strains of gut microbes known as bifidobacteria and lactobacilli, and those who unknowingly took a placebo for the same 21-day period.
The trial results, published in The Lancet on Thursday, run counter to findings from earlier tests, in which probiotics showed promise in reducing the risk of antibiotic-associated diarrhea and infections with the bug Clostridium difficile, which can cause life-threatening bowel inflammation.
The study may prompt some doctors to rethink whether to routinely prescribe probiotics along with antibiotics.
The low risk reductions in the study ‘‘question the cost-effectiveness of probiotics,’’ Daneman wrote. The test, dubbed Placide, is ‘‘a large and rigorous negative study, and we must judge whether it can tip the balance of probiotic evidence.’’
The market for probiotic supplements will be worth an estimated $2.07 billion by 2015 with sales growing almost 60 percent since 2010, according to a report by BCC Research. Demand is booming amid reports of health benefits ranging from improved digestion to better immunity.