Background: No standard methods exist for determining the onset of action of gastric antisecretory agents in human subjects.
Methods: Intragastric pH was measured when placebo, ranitidine 150 mg, ranitidine 75 mg or famotidine 10 mg were administered 30 min after the end of a meal.
Results: When the onset of action was defined as the earliest time that mean gastric pH with active treatment was statistically significantly higher (P < 0.05) than the corresponding placebo value, the onsets of action of ranitidine 75 mg and 150 mg were 55 min, and of famotidine 10 mg, 90 min. When onset was defined in terms of a particular decrease in gastric acid concentration for the group as a whole or for individual subjects, there was an important variation in the relative times of onset of ranitidine 75 mg and famotidine 10 mg.
Conclusions: When administered after a meal, the onset of action of ranitidine and famotidine on gastric pH can be determined for individual subjects as well as for the group as a whole. When onset was determined for the group using statistical significance, which does not depend on arbitrary cut-off points, ranitidine 75 mg had an earlier onset of action than did famotidine 10 mg.