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Probiotics Don't Prevent Antibiotic-Associated Diarrhoea?

Well, here is a bit of "guff" that needs some explanation. A newly published study on probiotics determined that they don't work to prevent antibiotic-associated diarrhoea (AAD) in elderly patients. However, the conclusion made by these researchers, including any media misrepresenting the data, just simple goes to show how little most people understand bacteria and probiotics.

Let's first look at the study details to understand why the results are almost meaningless. This was a well-designed (multi-centre, randomised, double-blind, placebo-controlled) study in nearly 3000 people. All participants were hospital inpatients aged 65 or over and had been prescribed one or more antibiotics. About half were asked to take a capsule containing a fixed dose of live bacteria (two strains of Lactobacillus acidophilusBifidobacterium bifidum, and Bifidobacterium lactis) per day for 21 days, and between antibiotic doses where possible. The other half formed the control group received a placebo with the same dosing instruction.

Researchers analysed stool samples from around half of the patients who experienced diarrhoea in order to determine whether their stomach upset had been caused by antibiotics, or by something else. Such analysis also allowed the researchers to track how many participants’ AAD was caused by C.difficile, which is the main cause of AAD (a growing concern as C.difficile becomes increasingly resistant to antibiotics and survives any treatment, causing problems).

The researchers found that the frequency and severity of AAD were similar in both groups, and both groups scored similarly in surveys assessing quality of life during the trial. Further, the number of people whose diarrhoea was caused by C. difficile was similar in both groups. All this data led the researchers to conclude that there is no evidence to support probiotics use in preventing AAD.

Unfortunately, this conclusion is far too broad and general. The effects of probiotics are strain-specific. Just because numerous strains of the bacterial species L.acidophilus (or B. bifidum or B. lactis) has shown to exert health benefits, it doesn't mean all strains within that species will have a similar effect. I recently discussed the importance of understanding bacteria at the strain-level a few weeks ago in a study on E. coli. I highly recommend you read it so I don't have to repeat myself here.

So knowing efficacy, the potency (cfu/g needed to see a benefit), and even safety are all related to the strain used, it's critical for people to understand that the strains used (in this study at hand) were strains that have never previously shown efficacy against AAD. Only logical conclusion that can be drawn is that these particular strains are not effective in preventing AAD--we can't generalize and say "probiotics" are ineffective. It's an inappropriate conclusion to draw from this single study on very specific strains--especially considering strain selection is the single most critical factor in selecting a probiotic.

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Source: Lactobacilli and bifidobacteria in the prevention of antibiotic-associated diarrhoea and Clostridium difficile diarrhoea in older inpatients (PLACIDE): a randomised, double-blind, placebo-controlled, multicentre trial

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