Aliases: Vitamin A, Preformed Vitamin A, Retinyl palmitate, Retinyl acetate
Pharmacological Mechanism
Retinol is oxidised to retinal (11-cis-retinal in rhodopsin → vision) and further to retinoic acid, which binds RAR/RXR nuclear receptors and regulates >500 genes controlling epithelial differentiation, immune function, and embryonic development. Stored in liver as retinyl esters; preformed vitamin A accumulates (unlike β-carotene where conversion is regulated).
Dosing Guidelines
PO: Typical 1467 mcg (Range: 700–3000 mcg)
Target Organ Systems
endocrine
immune-hematologic
Interactions
Isotretinoin (contraindicated): Additive hypervitaminosis A — preformed vitamin A and systemic retinoids share RAR/RXR-mediated toxicity (mucocutaneous, hepatic, pseudotumor cerebri). Supplemental vitamin A is held during an isotretinoin course. [Silverman 1987]