Fexofenadine is a pharmacologically active metabolite of Terfenadine, a non-sedating antihistamine. It is a second-generation, long lasting H₁ receptor antagonist which has a selective peripheral H₁ antagonistic action. Fexofenadine blocks the H₁ receptor and thus prevents activation of cells by histamine in the GI tract, large blood vessels and bronchial smooth muscle. This leads to relief of the allergic symptoms. Unlike most other antihistamines, Fexofenadine does not enter into the brain from the blood and therefore, does not cause drowsiness. Fexofenadine lacks the cardiotoxic potential, since it does not block the potassium channel involved in repolarization of cardiac cells.