EFFECT OF 22-OXACALCITRIOL ON HYPERPARATHYROIDISM OF DIALYSIS PATIENTS - RESULTS OF A PRELIMINARY-STUDY

Intermittent high dose administration of calcitriol or alfacalcidol is effective in suppressing secondary hyperparathyroidism in chronic dia lysis patients, however calcaemic action of these vitamin D derivative s is a major obstacle. 22-Oxacalcitriol (OCT) has been reported to hav e less calcaemic action than calcitriol, while preserving a comparable suppressive effect on parathyroid hormone (PTH) secretion. This preli minary study was conducted to examine the effects of OCT on secondary hyperparathyroidism in chronic dialysis patients. OCT was administrate d intravenously immediately after every haemodialysis session three ti mes a week for 12 weeks to three haemodialysis patients with secondary hyperparathyroidism. An initial dose of OCT of 5.5 mu g/haemodialysis session was increased stepwise by 5.5 mu g/haemodialysis up to 22 mu g/haemodialysis according to the suppression of PTH and calcaemic acti on. OCT was discontinued for at least a week when serum calcium adjust ed to albumin concentration measured just before haemodialysis exceede d 11.5 mg/dl. Marked reduction in plasma PTH, alkaline phosphatase and tartrate-resistant acid phosphatase was observed in all three patient s. Although the dose of OCT was increased to 22 mu g/haemodialysis in one patient, the final dose of OCT remained 5.5 mu g/haemodialysis in the other two patients because of hypercalcaemia. It is concluded that OCT is highly effective in suppressing PTH in dialysis patients with secondary hyperparathyroidism. Hypercalcaemia may be a major factor wh ich limits the use of OCT, though it may occur with higher doses of OC T than those of calcitriol usually given to suppress PTH hypersecretio n.