Successful treatment with captopril of an elderly man with polydipsia and hyponatremia.

A case of severe hyponatremia in a polydipsic 64-year-old man is described. He was unsuccessfully treated with both demeclocycline and lithium carbonate. However, low-dose captopril reversed the polydipsia and resulted in sustained normal serum sodium levels. We believe the antidipsogenic effect of captopril may benefit some patients with polydipsia and hyponatremia.