Diphenylhydantoin-induced Hyperglycemia and Impaired Insulin Release: Effect of Dosage

Elevated postprandial blood sugar levels were found in a forty-two-year-old Negro woman taking 400 mg. of diphenylhydantoin a day. After discontinuance of diphenylhydantoin, blood glucose levels and insulin responses were normal when oral and intravenous glucose tolerance tests and an intravenous tolbutamide test were performed. After taking 400 mg. diphenylhydantoin daily for two weeks the patient had decreased oral and intravenous glucose tolerance and an abnormal intravenous tolbutamide test with marked reduction in insulin response in all three tests. Oral glucose tolerance tests were within the limits of normal while the patient was receiving 300, 200, and 100 mg. diphenylhydantoin by mouth; however, the insulin response was decreased when the patient received 300 and 200 mg. diphenylhydantoin.