Methapyrilene kinetics and dynamics.

A study was undertaken to characterize the H1 receptor blockade, central nervous system depressant properties, and kinetic parameters of methapyrilene in man. Eight healthy subjects received, in random order at weekly intervals, placebo and methapyrilene 20 mg intravenously and 50 mg and 25 mg orally. Methapyrilene exhibited a moderate antihistaminic effect as measured by the reduction of histamine-provoked skin wheals. Sedation and drowsiness were detected only at the first sampling time (0.75 hr) after intravenous doses. The terminal plasma half-life ranged from 1.1 to 2.1 hr, apparent volume of distribution from 2.14 to 6.61 1/kg, and plasma clearance from 0.013 to 0.048 1/min/kg. Systemic bioavailability was low and showed large interindividual differences, ranging from 4% to 46%. Recovery of unchanged drug from the 24-hr urine was under 2% of the doses.