Effect of cimetidine on serum calcium levels in an elderly patient.

A 92-year-old woman with a normal serum calcium level received cimetidine postoperatively. She became severely hypocalcemic and exhibited tetany, seizures, and impaired mental status. Her condition responded to intravenous diazepam, phenytoin sodium, and gluconate calcium. Normal serum calcium levels were maintained by calcium infusions until the cimetidine treatment was stopped. Cimetidine may have been responsible for the observed complications due to its effect on serum parathyroid hormone level.