Vitamin A
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More Specific Terms
Dosage
- 1 mg = 3333 units severe deficiency:
- Capsule: 25,000 units, 50,000 units
Pharmacokinetics
- retinyl esters are storage forms of vitamin A
Adverse-effects
- not common (1-10%)
- irritability, vertigo, lethargy, malaise, fever, headache, drying or cracking of skin, hypercalcemia, weight loss, visual changes, hypervitaminosis
- 2-fold increase risk of fractures in postmenopausal women not taking hormone replacement therapy with high intake of vitamin A
- high serum levels of retinol (but not beta-carotene) associated with 1.6 fold increased risk of fracture in 50-75 year old men [4]
Drug-interactions
- carbamazepine: increased clearance of carbamazepine
- cholestyramine, mineral oil: decreased absorption of vit A
- oral contraceptives: increased absorption of vit A
- isotretinoin, etretinate: increased toxicity
- vitamin A can antagonize the ability of vitamin D to enhance Ca+2 absorption [3]
More General Terms
Additional Terms
References
- Drug Information & Medication Formulary, Veterans Affairs, Central California Health Care System, 1st ed., Ravnan et al eds, 1998
- Kaiser Permanente Northern California Regional Drug Formulary, 1998
- Prescriber's Letter 9(2):8 2002
- Journal Watch 23(5):42, 2003 Micahaelsson K et al Serum retinol levels and the risk of fracture. N Engl J Med 348:287, 2003 PMID: [1] Lips P Hypervitaminosis A and fractures. N Engl J Med 348:347, 2003 PMID: [2]
- Department of Veterans Affairs, VA National Formulary
