[A long-term comparative study of calcitriol versus alphacalcidol in patients with secondary hyperparathyroidism on...

Calcitriol has traditionally been the most widely used treatment for secondary hyperparathyroidism (SHPT) in uremic patients. There are currently no crossover equivalence studies of alphacalcidol versus calcitriol establishing which of the two derivatives is more active and better tolerated. The objective of this study was to compare the long term effect on control of PTH of similar doses of alphacalcidol versus calcitriol in the treatment of SHPT in these patients.

We conducted a retrospective study on 21 hemodialysis patients with stable SHPT of varying severity treated with intravenous calcitriol. In July 2002, the pharmacy of the reference hospital decided to substitute calcitriol for alphacalcidol based on the similarity of the two drugs. The conversion was made substituting a similar amount of drug. Mean absolute serum levels and percentage change in PTH, calcium and phosphorus were compared between the two periods and at 0, 3, 6, 9, 12 and 15 months after starting treatment with alphacalcidol. Student's t-test for paired means was used to compare the values between the two periods.

In the calcitriol period, mean PTH levels were 275.2 +/- 111.7 pg/ml. The mean dose of drug used was 1.7 +/- 0.8 mcg postdialysis, and serum calcium and phosphorus levels were 10.1 +/- 0,5 mg/dl and 5,2 +/- 0,9 mg/dl, respectively (p < 0.01). Mean dialysate calcium content was 2,9 +/- 0,3 mEq/l. In the alphacalcidol period, PTH increased (441.6 +/- 178.3 pg/ml) (p < 0.001) and the percentage of patients with PTH < 300 pg/ml decreased (24% at the end of the period), in spite of significantly increasing the mean drug dose (2,3 +/- 0,9 mcg postdialysis) (p < 0.05). Serum calcium levels did not show significant differences (10.2 +/- 0.7 mg/dl) (p = NS), but phosphorus control was improved (4,7 +/- 0,5 mg/dl) (p < 0.01). The percentage of patients with PTH < 300 pg/ml decreased progressively from the start of treatment with alphacalcidol from 75% to 24% at the end of follow-up. Our results seem to suggest that the dose of alphacalcidol and calcitriol are not equivalent and we need to increase the dose of alphacalcidol to obtain a similar result to calcitriol on suppression of PTH in uremic patients with SPTH.