Aminopropylidine diphosphonate (APD) in mild primary hyperparathyroidism: effect on clinical status

Mild hypercalcaemia associated with primary hyperparathyroidism has been increasingly recognized with the use of automated biochemical screening. Management is often difficult as symptoms are often absent or non-specific. Accordingly, we employed the hypocalcaemic effect of the diphosphonate APD to assess the effect of an acute fall in plasma calcium on indices of general well being, blood pressure, and vasoactive hormones in patients with mild primary hyperparathyroidism. Ten patients were studied in a randomized single blind, placebo-controlled cross-over study, using 30 mg APD intravenously or control saline infusion, over 2 h. Metabolic measurements, formal tests of muscle strength and cognitive function, and a standardized questionnaire were assessed 7 days after infusions. Albumin corrected plasma calcium was significantly lower (mean 2.49 +/- 0.04 SEM mmol/l) after APD when compared to control values (2.70 +/- 0.06 mmol/l, P less than 0.001). Twenty-four-hour urinary calcium, plasma magnesium and absolute monocyte count decreased significantly, whereas plasma parathyroid hormone increased after APD (P less than 0.05). There was no significant change in hypercalcaemic symptoms, muscle strength or cognitive function, and blood pressure, renin, aldosterone and atrial natriuretic peptide did not change. Side-effects, when they occurred, were mild. It is concluded that APD is a safe and effective means of lowering plasma calcium in mild primary hyperparathyroidism, but these acute reductions are associated with little or no improvement in clinical status in these patients.