Many more are freely available over the counter without needing a prescription.

Taking probiotics - strains of “good” bacteria - on top of a course of antibiotics may help ward off the diarrhoea that often comes with antibiotic treatment, according to a US review of past studies.

When researchers, whose findings appeared in the Journal of the American Medical Association, combined trials of all types of the gut-healthy microbes, they found that patients with a range of conditions - from ear infections to sepsis - were 42 percent less likely to get diarrhoea from their antibiotic drugs if they were also taking a probiotic.

One-quarter to one-third of people treated with an antibiotic typically get diarrhoea as a result, the researchers said. It's often not more than an unpleasant side effect, but can be serious enough to send some patients to the hospital.

“Antibiotics in doing their work actually kill off a lot of the normal flora that are supposed to exist in our gut, so things kind of go haywire,” said Sydne Newberry from the RAND Corporation in Santa Monica, California, who worked on the study.

Probiotics are strains of bacteria that research suggests can help replace some of the flora that antibiotics, especially so-called broad-spectrum antibiotics, wipe out.

“More than likely, what they do is they start to actually restore the normal bacteria in the gut, in the intestines,” Newberry said.

Probiotics can be bought over-the-counter as capsules, and are also present in some yogurt products.

Newberry's team reviewed 63 trials in which researchers had randomly assigned a total of almost 12,000 patients needing antibiotic treatment to probiotics, a placebo pill, or nothing.

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.

In a subset of 44 studies in which neither study participants nor the doctors treating them knew who was getting probiotics or placebo, the trials considered least prone to bias, patients on the probiotics were still 39 percent less likely to get diarrhoea.

The researchers couldn't tell whether one type of probiotic in particular was any better than others, especially since most of the studies used a combination of multiple bacteria strains. The most common probiotics used were from the genus Lactobacillus.

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.

Other experts said that further questions involved the size of the dose and how long it should be given.

Most of the studies were small and didn't report on side effects from the probiotics, but those that did concluded that the supplements seemed safe.

For that reason, while it's not clear that doctors should be giving out specific probiotics to all of their patients on antibiotic treatment - they may be harmful to small babies or very ill patients - it probably wouldn't hurt to try one, researchers said. - Reuters