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Summary
Mineral retention was measured during 39 metabolic balance studies in 34 patients with nutritional osteomalacia or late rickets; they were divided into 5 treatment groups consisting of oral vitamin D, artificial ultra-violet irradiation, 25-hydroxychole-calciferol {calcifediol), 1 α-hydroxycholecalciferol (alfacalcidol) and 1α,25-dihydroxy-cholecalciferol (calcitriol). With the 1 α-hydroxylated derivatives, initial dosage of 2 to 6 μg daily was required to achieve optimal healing rates by comparison with other responses. Mineral retention was markedly enhanced by supplementation with micro-crystalline hydroxyapatite compound (MCHC); untreated X-linked hypophosphataemic rickets healed in 7 weeks on 10 μg alfacalcidol daily and 6 g MCHC daily without developing hypercalcaemia. By contrast, adult-presenting hypophosphataemic osteomalacia developed early hypercalcaemia on the same treatment; additional phosphate supplementation, without changing other treatment, abolished hypercalcaemia and improved calcium retention. A long-term crossover trial of the vitamins D in 6 patients with hypoparathyroidism suggested that relative potencies were as follows {assigning to vitamin D an arbitrary potency of 1): vitamin D2 (or D3) 1: dihydrotachysterol (DHT) 3: calcifediol 10: alfacalcidol 750: calcitriol 1500. The two-fold superiority of calcitriol over alfacalcidol was evident. Calcifediol and vitamin D controlled plasma calcium at comparable levels of circulating 25-hydroxyvitamin D (25-OH-D), elevated 25-OH-D persisting at least 1 to 2 years after discontinuing long-term (>4 years) vitamin D. In 2 patients with myositis ossificans progessiva treated with 10 to 20 μg calcitriol daily, hypercalcaemia was minimized by a low-calcium diet supplemented with cellulose phosphate, suggesting that bone resorption did not play a major role in vitamin D intoxication. Net mineral loss was documented in a young male patient but not in a menopausal female, suggesting that calcitriol treatment was not likely to produce post-menopausal osteoporosis.