Clarithromycin is a macrolide antibiotic, which extends the duration of the heart's electrical activity, and it is this mechanism that is believed to increase the risk of fatal heart rhythms.
Researchers estimate the drug increases the risk by 76 per cent compared to penicillin V, another antibiotic with no known heart risks. In absolute terms, clarithromycin causes 37 cardiac deaths per 1 million courses of treatment, say researchers from Denmark.
The researchers discovered the risk after they analysed five million course treatments among Danish adults of clarithromycin, penicillin V and roxithromycin. During the 14 years of the study, 285 cardiac deaths were recorded, including 18 among those taking clarithromycin.
(Source: BMJ, 2014; 349: g4930)