Terfenadine

Overview
Terfenadine is an antihistamine formerly used for the treatment of allergic conditions. It was marketed under various brand names including Seldane in the United States, Triludan in the United Kingdom, and Teldane in Australia. It was superseded by fexofenadine in the 1990s due to the risk of cardiac arrhythmia caused by QT interval prolongation.

Terfenadine is a prodrug, generally completely metabolised to the active form fexofenadine by intestinal CYP3A4. Terfenadine itself, however, has a cardiotoxic effect and may be absorbed and reach myocytes if the patient is concurrently taking a CYP3A4 inhibitor (e.g. erythromycin, grapefruit juice).