Phenytoin-induced hyperglycemia.

A case of diabetic ketoacidosis in a 64-year-old black woman with maturity-onset diabetes receiving phenytoin for a seizure disorder is reported. The woman was admitted to the hospital with a one-day history of polyuria and polydipsia. For the 10 months before admission, her diabetes was controlled with isophane insulin suspension 27 units daily. She also took phenytoin 100 mg orally three times a day. This was prescribed approximately six weeks earlier for right-sided focal seizures that were detected by electroencephalogram during a previous hospitalization for nonketotic hyperosmolar coma. No other medications were taken. The patient was treated with i.v. fluids and intermittent doses of i.v. insulin. Her condition rapidly improved and insulin zinc suspension 35 units daily was prescribed on discharge. Phenytoin was discontinued because the seizure disorder was considered secondary to the previous episode of hyperosmolar coma. A literature review of phenytoin-induced hyperglycemia is presented, including previous case reports, possible mechanisms of action, monitoring guidelines, and potential therapeutic uses. If hyperglycemia occurs in a patient taking phenytoin, especially after starting phenytoin therapy or increasing the dose, drug-induced hyperglycemia should be considered in the differential diagnosis.