Table 6.
Chemical structure and pharmacokinetic characteristics of vitamin D compounds and activated forms.
Ergocalciferol | Cholecalciferol | Calcifediol (or Calcidiol) |
Calcitriol | |
---|---|---|---|---|
Chemical Structure |
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Absorption | Intestine (bile required) | Intestine (bile required) | Intestine, readily absorbed * | Intestine, readily absorbed * |
DBP dissociation constant | 10−7 | 10−7 | 10−9 | 10−7 |
Volume of distribution | very limited in plasma compartment; rapidly stored in fat tissue | very limited in plasma compartment; rapidly stored in fat tissue | larger than plasma volume | plasma compartment |
Tissue distribution for long-term | adipose tissue, muscle | adipose tissue, muscle | blood, adipose tissue, muscle | blood and tissues |
Circulating half-life | 2 days | 2 days | 3 weeks | 4–8 h |
Functional half-life | 2–3 months | ≤2 months | 2–3 months | 4–8 h |
* Faster absorption than ergocalciferol and cholecalciferol. DBP: vitamin D binding protein.