The effect of intravenous magnesium sulphate on parathyroid function in primary hyperparathyroidism

Ten patients with primary hyperparathyroidism caused by enlargement of a single parathyroid gland were studied preoperatively. An intravenous bolus of 4 g magnesium sulphate followed by a continuous infusion of 2 g per hour for 3 hours increased serum magnesium from 0.76 to 2.12 mmol/l (median values , p < 0.005). Serum C‐terminal parathyroid hormone (PTH) decreased from 94 to 78 pmol/l ( p < 0.005), and serum intact PTH from 7.0 to 4.8 pmol/l ( p < 0.008). The PTH changes preceded decreases in serum total calcium from 2.79 to 2.55 mmol/1 ( p < 0.01), and serum ionized calcium from 1.52 to 1.45 mol/1 ( p < 0.007). Urinary calcium excretion increased and urinary phosphate excretion decreased. Serum phosphorus, pH, albumin, creatinine, alkaline phosphatase, and urinary cyclic AMP showed no significant changes. The study showed that an intravenous magnesium sulphate infusion which at least doubled the normal serum magnesium concentration significantly suppressed PTH secretion in patients with primary hyperparathyroidism and subsequently reduced the serum calcium concentration .