Pharmacokinetics of the H2- receptor antagonist ranitidine in man.

1 Ranitidine pharmacokinetics were studied in six healthy volunteers. Following an overnight fast, doses of 20 mg intravenously 20, 40 and 100 mg orally and 100 mg orally with a standard meal, were administered to each subject on separate occasions. 2 Following intravenous administration there was a bioexponential decline in plasma levels from 576 +/- 56 ng/ml at 4 min to 10 +/- 2 ng/ml at 8 h. The distribution half-life (T 1/2 alpha) was 6.1 +/- 0.9 min, elimination half-life (T 1/2 beta) was 1.9 +/- 0.1 h, the volume of distribution (Vd beta) was 115 +/- 7 l and systemic plasma clearance (Cltp) was 709 +/- 62 ml/min. 3 Following 20 mg oral doses, peak levels were reached at 1.6 +/- 0.2 h and the systemic availability was 88 +/- 10%. Elimination half-life (T 1/2 beta) was unaffected by dose and the area under the curve increased linearly with dose and was unaffected by food. 4 Renal excretion (24 h) of unmetabolized ranitidine accounted for 50-70% of the dose with a further 1-3% appearing as desmethyl ranitidine.