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Antibiotics for chest infections reduce risk of pneumonia

Respiratory medicine

Respiratory medicine

A large cohort study, in the BMJ, has examined the protective effect of antibiotics against serious complications of common respiratory infections.

The study included more than 2.5 million cases of respiratory tract infection over ten years, using data from the UK General Practice Research Database. It examined patient outcome in the month following a consultation for URTI, sore throat, otitis media and chest infection and whether an antibiotic was prescribed. The primary outcome measure was the occurrence of complications, such as quinsy, mastoiditis and pneumonia, during this period.

For patients presenting with URTI, otitis media and sore throat, treatment with antibiotics made little difference to the likelihood of complications developing, with an NNT of more than 4,000.

However, prescribing antibiotics for a chest infection reduced subsequent cases of pneumonia, particularly in older patients, from 403 to 146 cases per 10,000, with an NNT of 39 in patients ? 65.

Perhaps surprisingly, the authors comment that there was no evidence that smoking status or underlying respiratory disease affected the risk of complications or the protective effect of antibiotics.

This was not a randomised trial and GPs' prescribing behaviour may have been influenced by the perceived severity of the disease and by the health of the patient, but if anything this would have further reinforced the benefits of antibiotics.

Perhaps GPs should feel a little less guilt when prescribing an antibiotic for a ‘bad chest' and have a little more resolve to avoid prescribing for other respiratory infections.

Petersen I, Johnson AM, Islam A et al. Protective effect of antibiotics against serious complications of common respiratory tract infections: retrospective cohort study with the UK general Practice Research Database. BMJ 2007 doi:10.1136/bmj.39345.405243.BE


Dr Peter Saul
GP, Wrexham and hospital practitioner in paediatrics (asthma and allergy)

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