Ranitidine bioavailability and kinetics in normal male subjects

Abstract

Ranitidine is a potent histamine H2-receptor blocker that inhibits histamine- and pentagastrin-induced gastric acid secretion. After doses of 100 mg both i.v. and orally ranitidine kinetics and bioavailability were investigated in a single dose 2-way crossover study in 12 normal men. Serum concentrations of ranitidine were determined by radioimmunoassay and urine concentrations by an ion-pair HPLC [high performance liquid chromatography] method. I.v. data were fitted to exponential equations with the computer program NONLIN; model-independent kinetic parameters were calculated. Elimination t1/2 [half-life], plasma clearance, renal clearance, hepatic clearance and volume of distribution for ranitidine after i.v. injection were 2 h, 10.4 ml/(min .times. kg), 7.2 ml/(min .times. kg), 3.1 ml/(min .times. kg), and 1.82 l/kg, respectively; after oral doses mean t1/2 was 2.7 h and mean bioavailability was 52%. The average cumulative urinary excretion of ranitidine as percent of dose was 69.4 .+-. 6.1 and 26.7 .+-. 7.2% after i.v. and oral doses.