Prospective comparison of the effects of maxacalcitol and of intravenous calcitriol on secondary hyperparathyroidism in chronic hemodialysis patients

To compare the effect of maxacalcitol and of intravenous calcitriol on secondary hyperparathyroidism, we conducted a 24-week prospective study for 20 chronic hemodialysis patients. Five or ten μg of maxacalcitol (5μg for patients with intact parathyroid hormone (PTH) less than 500pg/mL and 10μg for those with intact PTH higher than 500pg/mL) was administered intravenously to 10 patients, and 0.5 or 1.0μg of calcitriol (0.5μg for patients with intact PTH less than 500pg/mL and 1.0μg for those with intact PTH higher than 500pg/mL) was administered intravenously to 10 patients, at the end of every hemodialysis session. Dosage was changed according to PTH and serum calcium. We compared whole PTH, a new immunoradiometric assay exclusively for biologically active PTH (1-84), carboxy-terminal fragment (7-84) of PTH, intact PTH, bone-specific alkaline phosphatase (BAP), intact osteocalcin (iOC), amino-terminal propeptide of type I procollagen (PINP), serum calcium ajusted for albumin (Ca) and phosphorus (P).<br>Both maxacalcitol and calcitriol suppressed whole PTH 4 weeks after the start of administration. Calcitriol had less suppressing effect on whole PTH from 8 to 12 weeks of the study. From 16 to 24 weeks of the study, maxacalcitol and calcitriol showed almost equal whole PTH-suppressing effects. Intact PTH, 7-84 PTH, BAP, iOC and PINP showed almost similar changes as in whole PTH. However, the changes in BAP, iOC and PINP in patients treated with calcitriol were comparable. Ca increased and P showed no significant change. At the end of the study, there was no significant difference in these parameters between maxacalcitol and calcitriol. The effect of maxacalcitol was found to be 7 times higher than that of calcitriol.<br>In conclusion, maxacalcitol and calcitriol had almost equal effects on PTH, calcium and phosphorus, if dosages of these drugs are adjusted. The efficacy ratio of maxacalcitol to calcitriol was considered about 1:7.