Ranitidine kinetics and dynamics: II. Intravenous dose studies and comparison with cimetidine

Intravenous ranitidine has been shown to reduce pentagastrin‐stimulated gastric secretion. Eight normal men received, in randomized order, 60 mg ranitidine or 300 mg cimetidine intravenously over 2 min. Both ranitidine and cimetidine induced decreases in volume hydrogen ion content and pepsin activity of stimulated gastric juice. Ranitidine half‐life (t½) was 2.1 ± 0.1 hr and cimetidine (t½) was 1.5 ±0.1 hr. Ranitidine volume of distribution was 1.6 ±0.1 l/kg and that of cimetidine was 1.12 ± 0.12 l/kg. The clearance of ranitidine was 0.54 ± 0.04 l/kg hr −1 and that of cimetidine was 0.5 ± 0.05 l/kg hr −1 . It is suggested that the intravenous loading dose of ranitidine necessary to attain a serum concentration of 200 μg/l (which would achieve a 50% inhibition of gastric acid) is 0.3 mg/kg, followed by an infusion rate of 0.11 mg/kg hr −1 . Clinical Pharmacology and Therapeutics (1981) 30, 545–550; doi: 10.1038/clpt.1981.201