Human Pharmacology of Urapidil

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Abstract
Urapidil is a phenylpiperazine-substituted uracil derivative used in hypertension. It is rapidly absorbed when given by mouth. Peak blood concentrations of the slow release capsule occur 4 to 6 hours after administration. Oral bioavailability is 78% (range 72 to 84%) and distribution half-life and terminal half-life are about 35 minutes and 3 hours, respectively. Plasma clearance is 12 L/h and renal clearance 1.8 L/h. Seventeen percent appears in urine as the parent compound within 24 hours of dosing. There is extensive hepatic metabolism to the parahydroxylated(34% in urine), N-demethylated (4% in urine) and O-demethylated (3% in urine) products. Elimination is not saturable at usual clinical doses. The major action of urapidil is post-synaptic α1adrenergic blockade, with a minor degree of β1-adrenergic blockade and a centrally mediated reduction in sympathetic outflow which has an as yet unidentified basis.