Ten patients with
hypophosphatemic rickets (eight with X-linked familial form) were treated with
vitamin D2 (10,000 to 75,000 units per day) and oral
phosphate (1.5 to 3.6 gm) for a total of 438 treatment months.
Therapy was then changed to
calcitriol (17 to 34 ng/kg/day) and the same
phosphate dose. Patients served as their own controls, and significant biochemical changes noted were an increase in immunoreactive
parathyroid hormone from 29 +/- 9 (SD) microliters Eq/ml (pre-
phosphate) to 62 +/- 34 on
vitamin D2 plus PO4, then decreasing to 40 +/- 20 on a regimen of
1,25-dihydroxyvitamin D (1,25(
OH)2D) plus PO4; serum PO4 rose from 2.44 +/- 0.45 (SD) mg/100 ml to 3.06 +/- 0.79 and then to 3.43 +/- 0.76;
alkaline phosphatase activity decreased from 677 +/- 298 (SD) IU/liter to 457 +/- 183 to 290 +/- 176. Serum
calcium and
creatinine levels were unchanged. Both urinary
calcium excretion and
calcium-
creatinine ratio decreased after
therapy with 1,25(
OH)2D. Urinary
phosphate excretion was higher after
calcitriol administration. Serum 1,25(
OH)2D levels were low in these
vitamin D2-treated patients, and an inverse relationship between serum 25(
OH)D and 1,25(
OH)2D was found. Improved bone mineralization was evident from serial assessment by photon absorptiometry, and radial bone mineral content rose from 75.3% +/- 2.2% of expected to 82.2% +/- 1.4% (P less than .005). Stature was improved when assessed by standard deviation for chronologic age but did not reach statistical significance. Long-term 1,25(
OH)2D plus
phosphate therapy appears to be more efficacious than
vitamin D2 in this form of
rickets, particularly in improving
phosphate homeostasis.