Chronotherapy of high-dose 1,25-dihydroxyvitamin D3 in hemodialysis patients with secondary hyperparathyroidism: a single-dose study

Adsorption of oxacalcitriol by polysulphone haemodialyser in patients with secondary hyperparathyroidism

AIMS

This 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 given 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 microg) for 30 min into the arterial side of the dialyser in end-stage 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) mm, 0.41 (-0.43, 1.26) mg dl(-1) and 38 (-42, 88) pg ml(-1), respectively.

CONCLUSION

OCT is adsorbed by polysulphone dialyser in vitro and in vivo. However, the pharmacodynamic effectiveness was largely independent of the administration regimen of OCT given either during or at the end of haemodialysis.

Chronotherapy of high-dose active vitamin D3 in haemodialysis patients with secondary hyperparathyroidsm: a repeated dosing study

AIMS

Renal osteodystrophy is the major complication in patients with end-stage renal failure. Oral or intravenous vitamin D3 (D3) is given to these patients, but severe hypercalcaemia sometimes interrupts this therapy. This study was undertaken to determine whether the effectiveness and safety of D3 also depend on its dosing time during a repeated treatment.

METHODS

A higher dose (3 micro g) was given orally to 13 haemodialysis patients at 08.00 h or 20.00 h for 12 months by a randomized, cross-over design.

RESULTS

Three patients were withdrawn due to severe hypercalcaemia after switching from 08.00 h to 20.00 h dosings. The elevation in serum calcium concentration was significantly (P < 0.001) greater during the 08.00 h dosing in the remaining ten patients. Mean serum Ca concentration after the trial was 10.92 (95% confidence interval (CI) 10.79, 11.06) and 9.55 mg dl-1 (95% CI 9.30, 9.71) by 08.00 h and 20.00 h dosing, respectively. On the other hand, the suppression of the elevated serum parathyroid hormone (PTH) and subsequent increment in bone density were significantly greater during the 08.00 h dosing. Mean PTH concentration after the trial was 414 (95% CI 360, 475) and 220 pg ml-1 (95% CI 202, 249) by 08.00 h and 20.00 h dosing, respectively (P = 0.02). Mean increment of bone density after the trial was 22 (95% CI 8, 32) and 57 g cm-3 (95% CI 43, 83) by 08.00 h and 20.00 h dosing, respectively (P = 0.04).

CONCLUSION

These results indicate that a higher dose of oral D3 is more effective and safe after dosing at evening in patients with renal osteodystrophy.