Aliases: 1,25-(OH)₂-D3, 1α,25-dihydroxycholecalciferol, Rocaltrol, Active vitamin D
Pharmacological Mechanism
The fully activated vitamin D hormone — formed by renal CYP27B1 1α-hydroxylation of calcifediol. Binds VDR with ~1000× higher affinity than the precursors; drives the classical genomic actions (intestinal Ca²⁺/P absorption via TRPV6/calbindin, bone remodelling, PTH suppression). Narrow therapeutic window — skips all regulatory hydroxylation, so hypercalcemia and soft-tissue calcification are dose-limiting. Used clinically when the kidney cannot perform the 1α-hydroxylation step (CKD stage 4–5).
Dosing Guidelines
PO: Typical 0.333 mcg (Range: 0.25–0.5 mcg)
IV: Typical 0.333 mcg (Range: 0.25–0.5 mcg)
Target Organ Systems
endocrine
digestive
renal
musculoskeletal
Interactions
Vitamin D3 (caution): Concomitant D3 can unmask hypercalcemia; use only under monitoring.
Calcium (caution): Maximally stimulated Ca²⁺ absorption — risk of hypercalcemia is dose-proportional.
Magnesium (synergistic): Cofactor for VDR activation; ensure Mg sufficiency before dose escalation.