Cholecalciferol
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Cholecalciferol (vitamin D3)
Many OTC; Rx 50,000 IU also available
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Summary
Classes
Common uses
Vitamin D deficiency0, Osteomalacia0, Nutritional rickets0, Osteoporosis (adjunct to calcium and antiresorptives)0
Pharmacy
Starting dose
Maintenance 800-2,000 IU PO daily; deficiency replacement 50,000 IU PO weekly for 8-12 weeks then maintenance, or equivalent daily dosing 5,000-10,000 IU/d
Preparations
OTC 400, 1,000, 2,000, 5,000 IU softgels and tablets; Rx 50,000 IU capsules; liquid drops 400-2,000 IU/drop
US FDA Max
No strict; Institute of Medicine UL 4,000 IU/d in adults for chronic use
Pharmacology
Routes
Oral, IM (rare, for severe malabsorption)
Onset
Weeks to raise 25(OH)D into reference range
Duration
Long; fat-soluble storage in adipose
Half-life
~24 hours (parent); ~15 days (25(OH)D); tissue stores months
Bioavailability
~75% (oral; absorption improved with fat-containing meal)
Pregnancy
Safe at replacement doses; deficiency is itself a risk in pregnancy and lactation.[citation needed]
Legal status
OTC (most) and Rx-only (50,000 IU) in US
Purported mechanism
Cholecalciferol (D3) is the form synthesized endogenously in skin from 7-dehydrocholesterol under UVB; like ergocalciferol (D2), it is hydroxylated by hepatic CYP2R1 to 25-hydroxyvitamin D (the storage form measured clinically) and then by renal CYP27B1 to 1,25-dihydroxyvitamin D (calcitriol), the active hormone binding the vitamin D receptor (VDR).0 D3 is more potent than D2 at raising and sustaining serum 25(OH)D per dose, and is the more common OTC formulation; D2 remains the dominant Rx 50,000 IU formulation in the US for historical reasons.