Overview of the safety profile of the H2-receptor antagonists.

Reports of adverse drug reactions due to histamine H2-receptor antagonists (H2RAs) are rare considering their wide usage. Cimetidine produces central nervous system and endocrine toxicities more often than other H2RAs. Drug-drug interactions are of potentially greater concern with H2RAs, especially because the critically ill patient routinely receives many drugs. H2RAs may alter the absorption, metabolism, or renal excretion of concurrently administered drugs. Gastrointestinal absorption of drugs, such as ketoconazole, that dissolve poorly in the absence of adequate acid may be reduced. Inhibition of hepatic oxidative drug metabolism of agents such as warfarin, theophylline, and phenytoin, is primarily a problem with cimetidine. Adverse effects will be seen in predisposed individuals and the time course will depend on the pharmacokinetics of the object drug. The other H2RAs are less likely to inhibit drug metabolism and affect renal clearance of procainamide than is cimetidine.