Many drug interactions are the result of an alteration of CYP450 metabolism.10 The non-sedating antihistamines terfenadine (Seldane) and astemizole (Hismanal), and the gastrointestinal motility agent cisapride (Propulsid), were all withdrawn from the U.S. market because metabolic inhibition by other drugs led to life-threatening arrhythmias.11 The calcium channel blocker mibefradil (Posicor) was withdrawn from the U.S. market in 1998 because it was a potent enzyme inhibitor that resulted in toxic levels of other cardiovascular drugs.