[Relation of the kinetics of the antisecretory effect and kinetics of blood concentration in man. Comparing cimetidine and ranitidine].

The time course of antisecretory effects of ranitidine and cimetidine and their relationship to plasma concentration were studied in 4 healthy volunteers. Placebo, cimetidine (266 mg) or ranitidine (100 mg) were infused during one hour preceding the 90 minute assessment of food-stimulated gastric acid secretion (intragastric titration); cimetidine and ranitidine blood levels and gastric acid outputs were measured at 15 min intervals. For each test a significant (p less than or equal to 0.01) correlation was found between concentration and effect. The half-life effect of ranitidine (t1/2 E) was significantly (p less than or equal to 0.05) greater than t1/2 E of cimetidine whereas their plasma half-lives (t1/2) were similar. The ratio t1/2 E/t1/2 was significantly (p less than or equal to 0.05) lower with cimetidine than with ranitidine. Explanations for this discrepancy are analyzed according to various hypotheses. The determination of t1/2 E seems to be a good approach to the duration of action of H2-antagonists. Our results show that the ratio t1/2 E/t1/2 and the t1/2 E might be important pharmacokinetic parameters to compare various H2-receptor antagonists.