Vitamin-D treatment in hypoparathyroidism

Renal handling of calcium in hypoparathyroidism

Treatment of hypoparathyroidism usually requires the use of pharmacological doses of parent vitamin D or near physiological amounts of the hydroxylated metabolites, calcitriol or alphacalcidol. Vitamin D intoxication and hypercalcaemia may be a problem but can be minimised by the use of small doses of vitamin D or its metabolites combined with large amounts of oral calcium. The response to treatment can be easily monitored by measuring serum and urinary calcium and creatinine concentrations. This allows the derivation of two simple indices reflecting calcium load presented to the kidney (calcium excretion in mmol/l glomerular filtrate) and renal tubular calcium reabsorption (TmCa/GFR). These can be used to predict the requirement of calcium supplements and also identify those patients at particular risk of hypercalcaemia.

Calcitriol dosage in osteomalacia, hypoparathyroidism and attempted treatment of myositis ossificans progressiva

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-hydroxycholecalciferol (calcifediol), 1 alpha-hydroxycholecalciferol (alfacalcidol) and 1 alpha, 25-hydroxycholecalciferol (calcitriol). With the 1 alpha-hydroxylated derivatives, initial dosage of 2 to 6 micrograms daily was required to achieve optimal healing rates by comparison with other responses. Mineral retention was markedly enhanced by supplementation with microcrystalline hydroxyapatite compound (MCHC); untreated X-linked hypophosphataemic rickets healed in 7 weeks on 10 micrograms alfacalcidol daily and 6 grams 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 l): vitamin D2 (or D3) l: 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 (greater than 4 years) vitamin D. In 2 patients with myositis ossificans progressiva treated with 10 to 20 micrograms 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.

Vitamin D therapy in hypoparathyroidism and pseudohypoparathyroidism: weight-related dosages for initiation of therapy and maintenance therapy

The aims of this study were to determine the dose of vitamin D2 that maintains the serum calcium level within the normal range in hypoparathyroid and pseudohypoparathyroid children and to establish a safe and quickly acting dose for initiating therapy in symptomatic patients. The dose requirement for maintenance therapy was studied in 11 patients and initiation therapy was studied in five newly diagnosed hypocalcemic patients. The results show that (1) the maintenance requirement of vitamin D2 is proportional to body weight and averages 2,000 IU (50 microgram)/kg/day for children of all ages and with all types of hypoparathyroid disorders and the (2) in newly diagnosed symptomatic patients, carefully controlled administration of 8,000 IU (200 microgram) vitamin D2/kg/day for the first one to two weeks corrects hypocalcemia quickly and safely.

The interactions of thiazide diuretics with parathyroid hormone and vitamin D. Studies in patients with hypoparathyroidism

In order to clarify the mechanisms of thiazide diuretic-induced hypocalciuria, the effect of a thiazide was studied for 7 days in seven patients with hypoparathyroidism on Vitamin D and one on calcium infusion, and seven euparathyroid patients with hypercalciuria. In the control group, calcium excretion (mg/24 hr) fell by 44% from 415 to 232 within 4 days and remained at this level. Plasma total calcium corrected for total protein did not change. In the hypoparathyroid group, calcium excretion fell by 11% from 351 to 311 and then returned to the base line level. Plasma total calcium (mg/100 ml) increased from 10.09 to 10.88, 11.29 and 10.77 at the end of the 2nd, 4th, and 7th day of thiazide administration. In the patient having i.v. calcium and no Vitamin D, neither plasma nor urinary calcium changed significantly. In both groups sodium excretion increased on the first 2 days and fell to or below base line level thereafter. Urinary phosphate, magnesium, and potassium increased, plasma phosphate rose, and magnesium and potassium fell. It is concluded that: (a) The hypocalciuric effect of thiazides requires the presence of parathyroid hormone and is not solely a result of sodium depletion. (b) The hypercalcemic effect of thiazides in hypoparathyroidism is due to increased release of calcium from bone and requires the presence of a pharmacologic dose of Vitamin D. (c) Thiazides enhane the action of parathyroid hormone on bone and kidney; Vitamin D can replace parathyroid hormone in this interaction in bone but not in kidney.