Hypophosphatemic vitamin D-resistant rickets: metabolic balance studies in a child receiving 1,25 dihydroxyvitamin D3, phosphate, and ascorbic acid.

A child with hypophosphatemic vitamin D-resistant rickets was treated for three years with the conventional vitamin D-inorganic phosphate supplementation followed by a new therapeutic regimen consisting of 1,25 dihydroxyvitamin D3 (1,25 (OH)2D3) and half of the previous phosphate supplementation. The effectiveness of the two treatment regimens was compared by calcium, phosphate, and magnesium balance techniques and by serial radiological examinations as well as careful height measurements. In addition, the lowering of the urinary pH with ascorbic acid supplementation seems to be associated with improvement in the renal tubular reabsorption of phosphate, but its distinct effect, separate from the rest of the treatment modalities, was not tested in this study. The conventional treatment did not correct the hypophosphatemia and alkaline phosphatase elevation, whereas the 1,25 (OH)2 D3-inorganic phosphate regimen is well tolerated and effective in achieving a sustained normalization of these variables. In addition, the improved growth and healing of rickets further attest to the efficacy of the new treatment.