Excessive sensitivity to the hyponatremic effect of chlorpropamide in a patient with diabetes mellitus and anterior pituitary insufficiency.

A 67-year-old diabetic woman with undiagnosed anterior pituitary insufficiency developed hyponatremic coma within 5 weeks after initiation of chlorpropamide therapy. A provocation test with 500 mg chlorpropamide orally led within five hours to hyponatremia and sopor with high urinary sodium excretion. This rapid development of the hyponatremic syndrome excludes water retention due to ADH as the dominant cause. It is more probable that known defects in renal sodium conservation, brought about by the anterior pituitary failure, have been potentiated by chlorpropamide.