Effect of the mode of calcitriol administration on PTH-ionized calcium relationship in uraemic patients with secondary hyperparathyroidism.

To assess the effect of the different modes of calcitriol administration on PTH-ionized calcium relationship we conducted a prospective clinical trial in 33 patients on chronic haemodialysis with secondary hyperparathyroidism (four times upper normal limit intact PTH) who were randomly assigned, with stratification to PTH levels, to receive daily oral, intermittent oral, or intermittent intravenous calcitriol at the same dose of 0.045 micrograms/kg/weekly. PTH-iCa curves were generated by inducing hypo- or hypercalcaemia in sequential haemodialysis 1 week apart, before and after 10 weeks on treatment. All patients were dialysed against a dialysate calcium concentration of 2.5 mEq/l throughout the study period. After drop-outs, 26 patients completed the study: 11 on intravenous calcitriol (mean basal PTH +/- SD: 666 +/- 280 pg/ml), eight on intermittent oral calcitriol (mean basal PTH: 831 +/- 361), and seven on daily oral calcitriol (mean basal PTH: 719 +/- 280). Serum ionized calcium and phosphorus significantly increased in intravenous and daily oral groups after calcitriol treatment, but not in the intermittent oral group. Basal PTH did not significantly change in the three groups after 10 weeks on treatment. Maximal PTH significantly decreased in intravenous group (1449 +/- 660 versus 1122 +/- 691 pg/ml, P = 0.0085) and at the limit of statistical significance in the intermittent oral group (1701 +/- 774 versus 1445 +/- 634, P = 0.12), but it did not change in the daily oral group. Minimal PTH did not modify in the three groups. In all three groups, a shift to the right in the PTH-iCa relationships were observed, with significant changes in the set point of calcium.(ABSTRACT TRUNCATED AT 250 WORDS)