Hypomagnesaemia-induced hypocalcaemia: concentrations of parathyroid hormone, prolactin and 1,25-dihydroxyvitamin D during magnesium replenishment.

Three patients with hypomagnesaemia-induced hypocalcaemia were investigated during the phase of magnesium replenishment. Before treatment, serum levels of 25-hydroxyvitamin D and 1,25-dihydroxyvitamin D were at the lower limit of normal. In spite of a rapid rise of parathyroid hormone (PTH) after intravenous administration of magnesium, a reactive increase in 1,25-dihydroxyvitamin D in serum was absent or delayed. The increase of serum calcium into the normal range occurred before any consistent change in the concentrations of this vitamin D metabolite. The rise of serum prolactin in response to the increase in PTH was blunted or absent, and is a further example of a transient PTH resistance during the phase of magnesium replenishment.