When researchers combined trials of all types of probiotics, they found that patients with a range of conditions – from ear infections to sepsis – were 42% less likely to get diarrhoea if they were also taking a probiotic.
One-quarter to one-third of people treated with an antibiotic typically get diarrhoea as a result of their normal gut flora getting wiped out, researchers said.
"More than likely, what (probiotics) do is they start to actually restore the normal bacteria in the gut, in the intestines," said Dr Sydne Newberry from the RAND Corporation in Santa Monica, California, who worked on the study.
Lactobacillus probiotics are common
Her team reviewed 63 trials in which researchers had randomly assigned a total of almost 12 000 patients needing antibiotic treatment to probiotics or a placebo pill or nothing.
Dr Newberry and her colleagues calculated that 13 people being treated with antibiotics would need to take a probiotic for one case of diarrhoea to be prevented, according to findings published the Journal of the American Medical Association.
In a subset of 44 double-blind studies, patients on the probiotics were still 39% less likely to get diarrhoea.
The researchers couldn't tell from their analysis whether one type of probiotic in particular was any better than others, especially since most of the studies used a combination of multiple bacterial strains. The most common probiotics used were from the genus Lactobacillus.
Best strains to recommend unknown
Not being able to differentiate the benefits of different strains is a limitation, according to some researchers – because as with antibiotics, each strain of probiotic can have very different effects.
"You still can't take this information, go to a store, and grab a probiotic off the shelf and say, 'I know this is going to work,'" said Dr Shira Doron, who has studied probiotics and diarrhoea at Tufts Medical Center in Boston but wasn't involved in the new review.
"We don't really know which strains are the best to recommend," agreed Dr Mary Hickson, from Imperial College London.
What's more, "what we're not very clear on is exactly how big a dose we need to give, and for how long we should give it," Dr Hickson, who has also studied the effects of probiotics, said.
Probiotics are cheap
Probiotics can be bought over-the-counter as capsules for 50 cents to R1 per day, and are also present in some yoghurt products.
Most of the studies included in the analysis were small and didn't report on side effects from the probiotics. But those that did concluded the supplements seemed safe.
For that reason, while it's not clear doctors should be giving out specific probiotics to all of their patients on antibiotic treatment, it probably won't hurt to try one out, researchers said.
Probitics harmful to kids
"It's a relatively safe intervention (and) it's a relatively harmless intervention, so if you know you're prone to antibiotic-associated diarrheal, and if it's an antibiotic that's prone to cause antibiotic-associated diarrhoea, that's when I think of using it," Dr Doron said.
For small babies or very sick patients, however, researchers warned probiotics could be harmful.
Dr Doron told Reuters Health there's some evidence that probiotics may have a beneficial effect as an add-on therapy in patients with recurrent Clostridium difficile. But as with other types of antibiotic-related diarrhoea, there's a need for more research to come to definitive conclusions on which strains may help and which won't, she said.
(Genevra Pittman, Reuters Health, 2012)
(Photo of toilet paper from Shutterstock)