Risk of torsades de pointes from oral erythromycin with concomitant carbimazole (methimazole) administration

There are many reports of intravenous erythromycin causing QT prolongation and torsades de pointes, but this complication is seldom ascribed to orally administered erythromycin, which is by far the most commonly prescribed ro ute. This report describes a case of torsades de pointes associated with or al erythromycin as a result of a previously undescribed interaction with ca rbimazole, an antithyroid drug that is metabolized to the active drug methi mazole, and the potential pharmacokinetic and pharmacodynamic mechanisms ar e highlighted.