Cholecalciferol

Vitamin D analog, Fat-soluble vitamin

Cholecalciferol (vitamin D3)

Many OTC; Rx 50,000 IU also available

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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

Common uses

Classification(s)

Classes

Vitamin D analog, Fat-soluble vitamin

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.