The combination of clarithromycin and disopyramide can lead to dangerous QTc prolongation and Torsades de Pointes, likely due to CYP3A4 inhibition by clarithromycin.
May warrant QTc monitoring with clarithromycin-disopyramide co-use; hypothesis-generating case report leaves open interaction incidence and severity.
We report a 76-year-old woman who developed TdP ventricular tachycardia induced by combined use of clarithromycin and disopyramide. She had a history of myocardial infarction 5 years earlier and has taken disopyramide for supraventricular arrhythmias. In addition, she had taken clarithromycin for upper respiratory tract infection. On admission, an ECG showed prolongation of QTc interval to 0.71 seconds and self-terminating TdP occurred several times. Disopyramide was metabolized by the cytochrome enzyme CYP3A4 and clarithromycin competitively inhibits this enzyme, probably resulting in an increase in plasma concentration of disopyramide. We should consider this possibility when prescribing clarithromycin in combination with antiarrhythmic agent disopyramide.
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Hayashi et al. (1999) studied this question.
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