Cimetidine in elderly patients: review of uses and risks.

Cimetidine is widely prescribed but has numerous potential side effects, especially in elder patients, who require a lower dosage, e.g., 300 mg twice daily. Antacids may be more effective than cimetidine in preventing acute gastrointestinal bleeding in critically ill elderly patients. Cimetidine increases the risk of toxicity of other commonly used drugs such as phenytoin, diazepam, chlordiazepoxide, propranolol, theophylline, warfarin, and carbamazepine. Elderly patients taking cimetidine are at risk for neuropsychiatric changes, which may be temporarily reversed by physostigmine. Other side effects and indications for use are reviewed.