The combined use of intravenous and oral calcium for the treatment of vitamin D dependent rickets type II (VDDRII)

Abstract

Objective: Some patients with rickets are resistant to vitamin D and its analogues; we therefore assessed whether or not normal mineralization could be achieved in the absence of an intact 1,25(OH)2D3 receptor-effector system, by the use of intravenous high dose calcium infusion, followed by high dose oral calcium.

Design: We studied two patients with vitamin D dependent rickets type II and with absent responses to either high dose calcitriol or to oral calcium alone. Daily infusions equivalent to up to 1.4 g elemental calcium supplemented with oral phosphate were given for a period of 3.5 months for the elder sister and 2 months in the younger brother. Both patients were then treated by weekly calcium infusions for 5 months, followed by maintenance on oral calcium equivalent to up to 6 g elemental calcium per day.

Patients: Two siblings of consanguineous parents, a girl aged 28 months and a boy aged 10 months with vitamin D dependent rickets type II.

Measurements: Measurements of serum and urine calcium, phosphate and serum alkaline phosphatase were obtained before, during and after the calcium infusions. Twenty-four-hour urinary minerals, electrolytes, creatinine clearance, serum PTH and vitamin D metabolites were measured prior to calcium infusion, then repeated at 2-monthly intervals. Glomerular filtration rate, kidney ultrasound and CT scan were done at 6-monthly intervals. A scalp biopsy was done at the end of i.v. calcium treatment.

Results: The daily infusions of calcium supplemented with oral phosphate resulted in biochemical responses with normalization of calcium and phosphate in 3-5 days, and of alkaline phosphatase and PTH in 1.5-2 months. Radiological evidence of healing was seen in 42 days. A total of 3.5 months of daily calcium infusion in the elder sister and 2 months in the younger brother resulted in complete healing biochemically and radiologically, with improvement in height. The patients are under current follow-up, with no evidence of nephrocalcinosis or deterioration of glomerular filtration rate.

Conclusions: (a) The use of intravenous high dose calcium infusions followed by high dose oral calcium is an effective method of treatment of vitamin D dependent rickets type II. (b) The treatment was more effective since it was started early in the course of the disease and led to early healing and better growth with prevention of bone deformities. (c) Early treatment may also lead to improvement in alopecia, the mechanism for which needs to be elucidated.

Abbreviations: 1,25(OH)2D3, 1,25-dihydroxyvitamin D3 (calcitriol); 24-OHase, 25-(OH)D(3),24-hydroxylase; 1 alpha-(OH)D3, 1 alpha-hydroxyvitamin D3; 25(OH)D3, 25-hydroxyvitamin D3; 1 alpha-OHase, 1 alpha-hydroxylase; PTH, parathyroid hormone.