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Taking antibiotics? Probiotics may not prevent diarrhoea if you’re older

Probiotics - often called ‘friendly bacteria’ - do not reduce the chance of diarrhoea among older people taking antibiotics, a large study suggests.

BMJ Group News

What do we know already?

strawberry and yogurt

Antibiotics are widely prescribed to treat infections caused by bacteria. They usually work well and are safe, but some people do get side effects, including diarrhoea. Although the diarrhoea is typically mild, it can be more serious for people who are older or in poorer health, particularly if the diarrhoea is caused by bacteria called Clostridium difficile.

It’s not entirely clear why taking antibiotics increases the chance of diarrhoea, but researchers think it’s probably because antibiotics kill some of the helpful bacteria in the gut. This may allow harmful bacteria to multiply, leading to diarrhoea.

To help prevent this, doctors sometimes recommend taking probiotics along with antibiotics. These so-called ‘friendly bacteria’ are thought to replace some of the good bacteria killed by antibiotics. Probiotics are available in yoghurts and drinks, as well as in capsules.

Some studies have suggested that probiotics can help adults and children avoid diarrhoea when taking antibiotics. However, there hasn’t been much good-quality research about whether they help older people taking antibiotics.

Researchers have now done a large, high-quality study that included nearly 3,000 people aged 65 and older who were being treated with antibiotics in five hospitals in England and Wales. The people were randomly selected to take either a capsule containing probiotics for 21 days, or an identical capsule with no probiotics (a placebo). The researchers then compared how many people in the two groups got diarrhoea over eight weeks, and how often the diarrhoea was caused by Clostridium difficile.

What does the new study say?

The researchers found little difference between the groups - about 10 in every 100 people got diarrhoea whether they took the probiotic or placebo capsule.

There also wasn’t much difference in how many people had diarrhoea caused by Clostridium difficile, or in the severity of people’s diarrhoea, how long they stayed in hospital, or how they rated their quality of life.

How reliable is the research?

These findings should be reliable. This was a type of study called a randomised controlled trial, which is the best type of study for finding out the effects of a treatment. It was also ‘double blind’, which means that neither the participants nor the researchers knew until the end of the study who was taking the probiotics. As a result, people’s expectations and biases couldn’t influence the findings.

However, it’s worth noting that the study looked only at a specific group of people - those aged 65 and older who were receiving antibiotics in hospital. The probiotic capsules also included only four types of bacteria (two strains of lactobacilli and two strains of bifidobacteria). So we can’t be certain these findings apply to other groups of people, or to other combinations of probiotics.

What does this mean for me?

This study provides strong evidence that probiotics may not prevent diarrhoea among older people taking antibiotics. Experts will now need to weigh these findings against those from previous studies, to gauge whether this treatment is likely to help.

However, studies do agree that probiotics are generally safe. So, if you are older and decide to take probiotics along with an antibiotic, this is unlikely to harm you. We just don’t know whether it will help.

Published on August 09, 2013

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