Clarithromycin, one of the most commonly prescribed antibiotics, is used mainly to treat respiratory infections, but researchers have now found a link with fatal heart arrhythmia in some patients, with women in particular more likely to be affected.
Absolute risk is thought to be low, however, and GPs are advised to wait for further confirmation of the results before halting or changing drug prescriptions.
Researchers writing in the BMJ studied over 5m treatment courses among adults aged 40-74 in Denmark, who were prescribed seven-day courses of clarithromycin, roxithromycin or penicillin V between 1997 and 2011.
After adjusting for other factors, people taking a course of clarithromycin had a 76% higher risk of cardiac death compared to the control group on penicillin V, which has no known cardiac risk.
Clarithromycin is part of a class of antibiotics called macrolides, which are known to prolong the duration of electrical activity in heart muscle cells as a side-effect. The current study suggested this could result in fatal arrhythmia in some patients.
'Urgent' further research needed
The study suggested there would be 37 additional cardiac deaths per 1m courses with clarithromycin compared with the control group.
The researchers, from the Statens Serum Institut in Copenhagen, stressed that this absolute risk was low, and interpretation of its clinical importance was ‘delicate’.
They urged prescribers to wait until the results had been independently confirmed – which they have called upon other researchers to undertake ‘urgently’ – before changing how they prescribe the antibiotic.
But they also warned that, because many millions are prescribed the drug around the world each year, the total number of resultant, avoidable cardiac deaths ‘may not be negligible’.
They found that there was no ongoing increased risk of cardiac death after patients had completed their course of clarithromycin.
Current or past treatment with roxithromycin, which is also a macrolide, was not associated with an increased risk of cardiac death. The cardiac safety profiles of other macrolides will need to be studied in greater detail to help guide future clinical treatment decisions, researchers said.