Even for proponents, there are caveats
However, all the researchers recommending the use of probiotics did so with caveats. First and foremost, they advise clinicians that the term “probiotics” is an imprecise catchall and is essentially meaningless.
“A lot of products label themselves as probiotic. It’s a great marketing scheme, but many of the products out there aren’t really probiotics; they’re not proven with randomized control trials and don’t have the scientific background,” said Dr. McFarland. “We’ve found that the efficacy is extremely strain specific and disease specific. A strain may work for one disease and not work for another.”
In 2018, Dr. McFarland coauthored an evidence-based practical guide to help clinicians and patients identify the specific strain that works in certain indications. Dr. Cresci recommends that clinicians consult websites such as Probiotics.org or the National Institutes of Health’s database to find the strains that have been proven to work in well-designed clinical trials.
There was also agreement that, to date, the most robust data support probiotics for the treatment of antibiotic-associated diarrhea.
Although the optimal timing of probiotics is a subject of debate, most proponents agreed that the general rule is “the sooner the better.”
Dr. McFarland recommended incorporating probiotics within 24 hours of starting an antibiotic “because the damage done to your GI tract microbiome is pretty quick, and the probiotics work best if they’re established before major disruption occurs.” She added that patients should continue taking probiotics for 2-8 weeks after stopping antibiotics.
“It takes a long time for your normal flora to get restored,” she said. “It’s best to cover your bases.”
For others, the evidence is not definitive
Opinions on the value of probiotics to combat antibiotic-related GI side effects are divergent, though.
“I would not recommend the routine use of probiotics, and certainly not in the prevention of C. difficile or antibiotic-related diarrhea,” said David A. Johnson, MD, professor of medicine and chief of gastroenterology at Eastern Virginia Medical School, Norfolk. “I think the evidence does not support that, and I stand strongly on that recommendation.”
Dr. Johnson cited the 2020 guidelines from the American Gastroenterological Association, which offer only a conditional recommendation for the use of specific probiotics and only in preventing antibiotic-associated C. difficile infection.
Geoffrey A. Preidis, MD, PhD, an assistant professor of pediatrics in the section of gastroenterology, hepatology, and nutrition at Baylor College of Medicine, Houston, served as a coauthor of the AGA’s guidelines. He noted that after reviewing 39 published trials of approximately 10,000 patients given probiotics while receiving antibiotics, the authors “did find some evidence that specific probiotics might decrease the risk of C. difficile diarrhea, but the quality of that evidence was low.”
Dr. Preidis attributed this to the lack of well-designed multicenter trials that can isolate the effects of certain strains and determine their benefit in this application.
“The majority of published trials have not reported safety data as rigorously as these data are reported in pharmaceutical trials, so the risk of side effects could be higher than we think,” said Dr. Preidis. “As living microbes, probiotics can move from the intestines into the bloodstream, causing sepsis. Contamination in the manufacturing process has been reported. There might be other long-term effects that we are not yet aware of.”
When asked to characterize the available data on probiotics, Dr. Johnson replied, “I’d generally label it, ‘caveat emptor.’ ”
Dr. McFarland agreed that the field would benefit from better-designed studies and called out meta-analyses that pool outcomes with various strains for particular criticism.
“When researchers do that, it’s no longer valid and shouldn’t have been published, in my opinion,” she told this news organization.