Treatment of Vitamin D-Resistant Hypoparathyroidism With 25-Hydroxycholecalciferol

Twenty-five-hydroxycholecalciferol (25-HCC) is believed to be the biologically active metabolite of vitamin D₃circulating in the blood. Its clinical usefulness was determined in four patients with hypoparathyroidism, three of whom were resistant to vitamin D. Two patients with Vitamin D resistance responded to 25-HCC (5,000 units or less per day) with a significant increase in serum calcium concentration and in urinary calcium excretion. A similar response was shown in a patient with idiopathic hypoparathyroidism who was probably not vitamin D-resistant. In all three patients, 25-HCC significantly increased the gastrointestinal absorption of calcium. In one patient, it increased the urinary excretion of hydroxyproline. In a fourth patient, who had shown resistance to dihydrotachysterol and cholecalciferol, 25-HCC did not significantly affect serum calcium concentration. This patient, unlike the rest, had a degree of moderate renal failure.