The metabolite of seldane (terfenadine), fexofenadine, was launched in the USA. A histamine H1 receptor antagonist, fexofenadine is more effect
than its parent compound without the associated side-effects.
Fexofenadine HCl (Allegra) is a selective, specific H1 antagonist that is structurally
related to the butyrophenone tranquilizer haloperidol. It is the active
carboxylic acid metabolite of terfenadine (no longer commercially available in
the United States). It binds mainly to the peripheral H1 receptors, with minimal
crossing of the blood–brain barrier and hence minimal sedative effects. Fexofenadine
lacks the cardiotoxic effects of its parent drug, terfenadine. However, it has
been associated with increased QT interval, syncope, and ventricular arrhythmia
in at least one susceptible patient with preexisting cardiovascular risk. To date, no
significant interactions have been demonstrated with fexofenadine when administered
concomitantly with azole antifungals or macrolide antibiotics. Indicated
for seasonal allergic rhinitis and chronic idiopathic urticaria.
