Hypocalcemia after therapeutic use of magnesium sulfate.

It is now recognized that magnesium plays an important role in calcium homeostasis. Although the effects of hypomagnesemia have been frequently reported, little has been written to suggest a clinically important role for hypermagnesemia. A case is reported in which severe hypocalcemia, with a low plasma parathyroid hormone (PTH) concentration, resulted from the therapeutic use of magnesium sulfate for toxemia of pregnancy. Following recovery, the parathyroid glands were shown to respond normally to a phosphate load. It is suggested that the hypermagnesemia directly suppressed PTH secretion, resulting in symptomatic hypocalcemia.