Evidence Summary

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In people prescribed antibiotics, probiotics reduce the risk of getting C. difficile-associated diarrhea, without causing important side effects

Johnston BC, Ma S, Goldenberg JZ, et al. Probiotics for the prevention of Clostridium difficile-associated diarrhea: a systematic review and meta-analysis. Ann Intern Med 2012;157:878-88.

Review question

In adults and children receiving antibiotics, how effective and safe are probiotics for the prevention of C. difficile-associated diarrhea?


C. difficile bacteria cause severe diarrhea and other bowel diseases. C. difficile-associated diarrhea occurs most often in hospitalized older people receiving antibiotics. C. difficile is involved in about one third of cases of diarrhea linked to the use of antibiotics. A Canadian study of 136,877 hospital admissions showed that 1 of every 10 patients who get C. difficile will die because of it.

Probiotics are microorganisms that may counter the disturbances in the bowel. They may also reduce the risk of the spread of bad bacteria.

Common types of probiotics are L. acidophilus, L. casei, L. rhamnosus, and S. boulardii. They are increasingly available at health food stores and supermarkets as capsules and dairy-based food supplements. Their cost and occurrence of side-effects are low.

How the review was done

This summary is based on a systematic review and meta-analysis that included 20 randomized controlled trials including 3,818 adults and children. Trials were published between 1989 and 2011.

What the researchers found

Among people who had been prescribed antibiotics, probiotics reduced the number of cases of C. difficile-associated diarrhea by 66% compared with not taking a probiotic or taking a placebo.

In a population in which 5% of cases get antibiotic-related C. difficile-associated diarrhea, probiotics would prevent 33 episodes per 1,000 people. The use of probiotics did not cause any side-effects.

Strong evidence supports the protective effect of probiotics in preventing C. difficile-associated diarrhea.


In people taking antibiotics, probiotics reduce C. difficile-associated diarrhea by 66%.

Probiotics compared with no probiotics in patients receiving antibiotic treatment



No probiotics

C. difficile-associated diarrhea*



Adverse effects†



*Statistically significant difference.

†Most commonly abdominal cramping, nausea, fever, soft stools, flatulence, and taste disturbance


Advanced statistical methods contrasting and combining results from different studies.
A harmless, inactive, and simulated treatment.
Randomized controlled trials
Studies where people are assigned to one of the treatments purely by chance.
Systematic review
A comprehensive evaluation of the available research evidence on a particular topic.

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