Alpha adrenergic blocking activity of urapidil in man

Urapidil is a new antihypertensive vasodilator agent whose pharmacologic action in man has not yet been fully defined. We have assessed the alpha adrenergic blocking activity of urapidil 15 and 30 mg given intravenously in a single blind study in 8 healthy volunteers. Urapidil produced dose-dependent parallel shift of the phenylephrine log dose/blood pressure response curve, consistent with significant competitive peripheral alpha 1 antagonism. Mean dose ratios were 2.99 and 5.48 for the 15 mg and 30 mg doses respectively. The pA2 for alpha 1 blockade is 7.3. Given these data, the major mechanism of antihypertensive effect of urapidil may be alpha 1 antagonism in the peripheral vasculature.