Intravenous calcitriol lowers serum calcium concentrations in uraemic patients with severe hyperparathyroidism and hypercalcaemia

We studied the effects of intravenous calcitriol in four persistently hypercalcaemic patients established on haemodialysis. All had marked hyperparathyroidism and had been previously shown to be intolerant to vitamin D by mouth. Calcitriol was administered at the end of each dialysis session in doses of 0.5-2.5 micrograms for 2 months and continued for 7 and 8 months in two patients. A significant decrease in serum calcium was observed after 2 weeks, which was maintained throughout treatment despite increasing the dose of calcitriol. This was associated with a decrease in serum concentrations of iPTH (28% of the initial value at 4 weeks), suggesting a shift in the set-point for PTH secretion. During longer-term treatment, serum calcium values increased, but lower concentrations of iPTH were maintained. We conclude that an increment in serum calcium is not a prerequisite for the suppressive action of calcitriol on parathyroid secretion and that the presence of hypercalcaemia does not preclude its use. Longer-term studies on a larger number of patients are required to assess the therapeutic potential of intravenous calcitriol in hypercalcaemic patients.