Drug interactions with antisecretory agents.

Antisecretory agents may affect the absorption, metabolism, and renal excretion of other drugs. Inhibition of gastric acid secretion may decrease the gastrointestinal absorption of drugs such as ketoconazole that dissolve poorly in the absence of adequate acid. With anti-secretory agents, the drug interaction mechanism most likely to result in adverse effects is the inhibition of hepatic oxidative drug metabolism, primarily a problem with cimetidine. Omeprazole also appears to inhibit the hepatic metabolism of some drugs, but available evidence indicates that it interacts with fewer drugs than cimetidine and the magnitude of the inhibition is lower. Cimetidine decreases the renal clearance of procainamide and its active metabolite, N-acetylprocainamide, probably through interference with active renal tubular secretion. In therapeutic doses, other H2-receptor antagonists probably have minimal effects on renal procainamide elimination.