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

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Abstract
Ranitidine i.v. was shown to reduce pentagastrin-stimulated gastric secretion. Normal men (8) received, in randomized order, 60 mg ranitidine or 300 mg cimetidine i.v. over 2 min. Both ranitidine and cimetidine induced decreases in volume H+ content and pepsin activity of stimulated gastric juice. Ranitidine half-life (t1/2) was 2.1 .+-. 0.1 h and cimetidine (t1/2) was 1.5 .+-. 0.1 h. Ranitidine volume of distribution was 1.6 .+-. 0.1 l/kg and that of cimetidine was 1.12 .+-. 0.12 l/kg. Ranitidine clearance was 0.54 .+-. 0.04 l/kg per h and that of cimetidine was 0.5 .+-. 0.05 l/kg per h. The i.v. loading dose of ranitidine necessary to attain a serum concentration of 200 .mu.g/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 per h.