Terfenadine

Terfenadine, formerly marketed under the brand name Seldane, is an antihistamine used for the treatment of allergic conditions.

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 (including grapefruit juice).

The risk of cardiac arrhythmia has meant that terfenadine has largely been superceded by fexofenadine preparations.