Br J Clin PharmacolBritish Journal of Clinical Pharmacology DOI:10.1111DOI:10. /j.1365DOI:10. -2125DOI:10. .2004
AimsThis study was undertaken to evaluate removal of 22-oxacalcitriol (OCT), an active and intravenously used vitamin D3 analogue with less calcaemic activity, by polysulphone haemodialyser in vivo and in vitro . We further compared the pharmacodynamic efficacy [suppression of intact parathyroid hormone (iPTH)] when g iven intravenously either during or at the end of the haemodialysis.
Methods(i) Drug clearance by the polysulphone dialyser was measured during a single continuous infusion (5 m g) for 30 min into the arterial side of the dialyser in endstage renal failure patients with secondary hyperparathyroidism ( n = 7). (ii) The drug adsorption by the hollowfibre membrane during incubation for 30 min was measured in vitro . (iii) To evaluate efficacy, the drug was given (i.v. bolus) during or at the end of haemodialysis for 4 weeks in a cross-over fashion with a washout period of 8 weeks ( n = 9). Serum Ca 2 + , phosphate (P) and iPTH concentrations just before the initiation of the dialysis were monitored every week.
Results(i) OCT was significantly cleared by the polysulphone haemodialyser, but the clearance declined in a time-dependent manner to approach zero at 30 min. Arterial (at the place between the drug infusion site and the haemodialyser column) drug concentrations did not change during the infusion (mean = 2064 ± 233 pg ml -1 ). Venous (just after the dialyser) drug concentrations at 10 min after the infusion were significantly lower than those of the arterial side (mean = 784 ± 84 pg ml -1 ); however, they increased with time and reached those of the arterial side at 30 min. (ii) In vitro , OCT was adsorbed by the membrane. The amount of adsorption was concentration-dependent and was lower in the presence of human serum (55 ± 4% without and 23 ± 4% with serum at 600 pg ml -1 of OCT). (iii) Although serum Ca 2 + and P increased and iPTH decreased by both treatment regimens (i.e. OCT administered either during or at the end of haemodialysis), these changes did not significantly differ. Mean differences (and 95% confidence interval) of Ca 2 + , P, and iPTH at the end of the trial were 0.03 ( -0.04, 0.09) m M , 0.41 ( -0.43, 1.26) mg dl -1 and 38 ( -42, 88) pg ml -1 , respectively.
ConclusionOCT is adsorbed by polysulphone dialyser in vitro and in vivo . However, the pharmacodynamic effectiveness was largely independent of the administration reg imen of OCT given either during or at the end of haemodialysis.
Adsorption of oxacalcitriol by haemodialyserBr J Clin Pharmacol 58 :5 489