EFFECTIVE SUPPRESSION OF PARATHYROID-HORMONE BY 1-ALPHA-HYDROXY-VITAMIN-D-2 IN HEMODIALYSIS-PATIENTS WITH MODERATE TO SEVERE SECONDARY HYPERPARATHYROIDISM

Calcitriol, as used for treating secondary hyperparathyroidism, has a low therapeutic index. The safety and efficacy of the vitamin D analog , 1 alpha(OH)-vitamin D-2 (1 alpha D-2), which has less toxicity in an imals than 1 alpha(OH)-vitamin D-3, was tested in a multicenter study of 24 hemodialysis patients with secondary hyperparathyroidism [serum intact (i) PTH > 400 pg/ml]. Calcium-based phosphate binders alone wer e used to maintain serum phosphorus less than or equal to 6.9 mg/dl. A fter eight weeks without calcitriol (washout), oral 1 alpha D-2, 4 mu g/day or 4 mu g thrice weekly, was started, with thr dose adjusted ove r 12 weeks to maintain serum IPTH between 130 and 250 pg/ml. Pre-treat ment serum iPTH fell from 672 +/- 70 pg/ml (SEM) to 289 +/- 36 after t reatment (P < 0.05). The maximal decrease in serum iPTH was 48 to 96%, with 87.5% of patients reaching target IPTH levels. The final dose of 1 alpha D-2 averaged 14.2 mu g/week. Pre-treatment serum calcium rose modestly from 8.8 +/- 0.2 mg/dl to 9.5 +/- 0.2 after treatment (P < 0 .001). Only once did modest hypercalcemia (serum Ca > 11.2 mg/dl) nece ssitate stopping treatment. Neither the average serum P level, the inc idence of hyperphosphatemia, nor the dose of phosphate binders changed from washout to treatment. Thus, oral 1 alpha D-2, is highly efficaci ous in suppressing secondary hyperparathyroidism in hemodialysis patie nts and is safe despite exclusive use of calcium-based phosphate-binde rs. Future studies should clarify the optimal dosage regimen.