12 CLINICAL PHARMACOLOGY
12.1 Mechanism of Action
Doxercalciferol is a synthetic vitamin D2 analog that requires metabolic activation to form the active 1α,25-(OH)2D2 metabolite, which binds to the vitamin D receptor (VDR) to result in the selective activation of vitamin D responsive pathways. Vitamin D and doxercalciferol have been shown to reduce PTH levels by inhibiting PTH synthesis and secretion.
In healthy volunteers, peak blood levels of 1α,25-(OH)2D2, the major metabolite of doxercalciferol, are attained at 8 hours after a single intravenous dose of doxercalciferol.
The mean elimination half-life of 1α,25-(OH)2D2 after an oral dose is approximately 32 to 37 hours with a range of up to 96 hours.
Patients with renal impairment
The mean elimination half-life of 1α,25-(OH)2D2 in patients with end-stage renal disease (ESRD) and in healthy volunteers appears to be similar following an oral dose. Doxercalciferol Injection is not approved for oral use.
Hemodialysis causes a temporary increase in 1α,25-(OH)2D2 mean concentrations, presumably due to volume contraction. 1α,25-(OH)2D2 is not removed from blood during hemodialysis.