Drug interactions of H2-receptor antagonists.

Three drug interactions of nizatidine and of other antisecretory agents were studied comparatively. First, the effects of nizatidine, cimetidine and ranitidine on the dispositional kinetics of theophylline were evaluated in chronic obstructive pulmonary disease (COPD) patients. Second, the effect of magnesium/aluminium hydroxide on the relative bioavailability of nizatidine, famotidine, cimetidine and ranitidine was evaluated in healthy volunteers. Finally, the effects of nizatidine and omeprazole on the dispositional kinetics of phenytoin were evaluated in healthy volunteers. Only cimetidine altered the steady-state kinetics of oral theophylline, slowing theophylline clearance by 25%. Each of the H2-receptor antagonists exhibited a modest decline in relative bioavailability when ingested with antacid. Antacid ingestion decreased the bioavailability of famotidine, ranitidine and cimetidine by 20-25%, and the bioavailability of nizatidine by 12%. Each of these effects was statistically significant. Finally, it was found that neither omeprazole nor nizatidine affected the single dose kinetics of phenytoin.