Ergocalciferol
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Ergocalciferol (vitamin D2)
Drisdol, Calcidol; also many OTC preparations
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Summary
Classes
Common uses
Vitamin D deficiency0, Osteomalacia0, Hypoparathyroidism (with calcium)0, Nutritional rickets0
Pharmacy
Starting dose
Deficiency: 50,000 IU PO weekly for 8-12 weeks, then maintenance 800-2,000 IU/day; maintenance OTC dosing typically 800-2,000 IU/d
Preparations
50,000 IU capsules (Rx); 8,000 IU/mL oral solution (Rx); 400-5,000 IU OTC tablets and softgels
US FDA Max
Not strictly fixed; long-term Upper Limit ~4,000 IU/d in adults (Institute of Medicine)
Pharmacology
Routes
Oral
Onset
Days to weeks to raise 25(OH)D; clinical effect on bone over months
Duration
Long; fat-soluble, stored in adipose
Half-life
~24 hours (parent); ~15 days (25(OH)D); 25(OH)D stores persist for months[1]
Bioavailability
~75% (oral; fat-soluble, absorption requires intact biliary/lipid digestion)[1]
Pregnancy
Safe at replacement doses; deficiency is itself a risk in pregnancy and lactation.[citation needed]
Legal status
OTC (low-dose) and Rx-only (50,000 IU and concentrated solutions) in US
Purported mechanism
Ergocalciferol (D2) and cholecalciferol (D3) are hydroxylated in the liver by CYP2R1 to 25-hydroxyvitamin D (the storage form measured clinically) and then in the kidney by CYP27B1 to 1,25-dihydroxyvitamin D (calcitriol), the active hormone that binds the vitamin D receptor (VDR) to drive transcription of genes governing intestinal calcium absorption, bone mineralization, and broad immunomodulation.0 D3 (cholecalciferol) is more potent at raising serum 25(OH)D per dose; D2 remains widely prescribed in the US Rx 50,000 IU formulation[1].
References
- ↑ 1.0 1.1 1.2 FDA Prescribing Information, Drisdol (ergocalciferol), Sanofi-Aventis, current revision. https://www.accessdata.fda.gov/drugsatfda_docs/label/2017/006535s029lbl.pdf