Terfenadine occurs as prodrug, generally wholly metabolised to the active form fexofenadine by intestinal CYP3A4. Terfenadine itself, all the same, has the cardiotoxic consequence & can be absorbed & email myocytes whenever the patient is at the same time ingesting a CYP3A4 inhibitor (e.g. erythromycin, grapefruit juice).

A chance of arrhythmia has intended that terfenadine has largely been superseded by fexofenadine preparations.