Terfenadine: Where do we stand?
The United States Food and Drug Administration (FDA) recently withdrew terfenadine (Seldane; Hoechst Marion Roussel) from the market. Terfenadine was introduced almost 17 years ago as the first nonsedating antihistamine. Since 1992 it has been known that both terfenadine and astemizole (Hismanal; McNeil Consumer Products) are cardiotoxic in a dose-dependent fashion. The risk of ventricular arrhythmia is increased in the presence of liver disease, cardiac disease, electrolyte imbalance, overdose or the presence of drugs that inhibit drug clearance. While terfenadine is cardiotoxic, its active metabolite, fexofenadine, is not. Fexofenadine is now marketed as Allegra (Hoechst Marion Roussel) in the United States but is still under review in Canada. Because patients who take terfenadine can now use fexofenadine, the FDA made a move to protect patients. In Canada we have a different situation, which requires a different management strategy. Patients should not be started on terfenadine or astemizole, but if they feel they cannot change drugs, then they must be informed of the risks. This is the responsibility of the physician and pharmacist.