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 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 hospitals and doctors to rethink whether to routinely prescribe probiotics along with antibiotics, Nick Daneman, of the University of Toronto's Sunnybrook Health Sciences Center, wrote in a commentary accompanying the research.
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, a U.S. market researcher. Demand is booming amid reports of health benefits ranging from improved digestion to better immunity.
The patients, age 65 and older, were selected at three hospitals in south Wales and another two in northeast England. Neither the patients nor the staff knew who was receiving a placebo and who got probiotics.
The researchers, led by Stephen Allen of Swansea University's College of Medicine, started out with evidence from other studies that suggested probiotics would show an impact on diarrhea as well as Clostridium difficile.
Now that the results are in, "we believe that there is insufficient evidence to support the use of any microbial preparation for the prevention of antibiotics-associated diarrhea in older inpatients," Allen and his colleagues wrote in the study paper.
The researchers acknowledged some flaws in the study. The scientists weren't able to reliably exclude patients who might have biased the results because they were prone to episodes of diarrhea, for example. Many of the diarrhea episodes were so short that the researchers failed to collect stool samples for testing in about 40 percent of the participants, an issue reported in other, smaller trials.
Britain's National Institute for Health Research and the Health Technology Assessment program funded the study. Allen disclosed that in the past he had been an invited guest at the Yakult Probiotic Symposium and had received research funding from Yakult Honsha Co., the maker of probiotic dairy drinks.