Drug information of Vitamin A

Vitamin A

Drug group:

Retinol and derivatives of retinol that play an essential role in metabolic functioning of the retina, the growth of and differentiation of epithelial tissue, the growth of bone, reproduction, and the immune response. Dietary vitamin A is derived from a variety of carotenoids found in plants. It is enriched in the liver, egg yolks, and the fat component of dairy products.

Mechanism of effect

Vision:

Vitamin A (all-trans retinol) is converted in the retina to the 11-cis-isomer of retinaldehyde or 11-cis-retinal. 11-cis-retinal functions in the retina in the transduction of light into the neural signals necessary for vision. 11-cis-retinal, while attached to opsin in rhodopsin is isomerized to all-trans-retinal by light. This is the event that triggers the nerve impulse to the brain which allows for the perception of light. All-trans-retinal is then released from opsin and reduced to all-trans-retinol.

All-trans-retinol is isomerized to 11-cis-retinol in the dark, and then oxidized to 11-cis-retinal. 11-cis-retinal recombines with opsin to re-form rhodopsin. Night blindness or defective vision at low illumination results from a failure to re-synthesize 11-cis retinal rapidly. 

Epithelial differentiation:

The role of Vitamin A in epithelial differentiation, as well as in other physiological processes, involves the binding of Vitamin A to two families of nuclear retinoid receptors (retinoic acid receptors, RARs; and retinoid-X receptors, RXRs). These receptors function as ligand-activated transcription factors that modulate gene transcription. When there is not enough Vitamin A to bind these receptors, natural cell differentiation and growth are interrupted.

Pharmacokinetics

  • Serum concentration: 300-700 ng/mL (adults); 200-500 ng/mL (infants)
  • Peak plasma time: 4-5 hr (oil solution); 304 hr (water-miscible)
  • Protein Bound: Retinol binding protein
  • Distribution: Mainly stored in liver as retinyl palmitate
  • Metabolism: hepatic glucuronidation, decarboxylation
  • Metabolites: retinoic acid, retinal
  • Excretion: Urine and feces (via bile)

Dosage

Adult

Dosage Forms

capsule

  • 7,500 U
  • 8000 U
  • 10,000 U
  • 25,000 U

injectable solution

  • 50,000 U/mL

tablet

  • 10,000 U
  • 15,000 U

RDA

Described as retinol activity equivalent (RAE)

1 RAE = Retinol 1 mcg

Males: 900 mcg/day (3000 U/day)

Females

  • 700 mcg/day (2330 U/day)
  • >18 years pregnant: 750-770 mcg/day (2500-2600 U/day)
  • >18 years breastfeeding: 1300 mcg RAE (4330 U)

Upper Intake Levels

>18 years: 3000 mcg/day RAE (10,000 U)

Pregnancy: 3000 mcg/day RAE (10,000 U)

Lactation: 3000 mcg/day RAE (10,000 U)

Vitamin A Deficiency

Malabsorption or oral administration not feasible: 100,000 U/day IM for 3 days; then 50,000 U/day for 2 weeks; follow with oral therapy.

Oral therapy: Take oral therapeutic multivitamin containing 10,000-20,000 U/day vitamin A for 2 months

Deficiency prophylaxis: 10,000-50,000 U PO qDay

Xerophthalmia (Off-label)

Recommended dose except for females of reproductive age: 200,000 units PO qDay for 2 days; repeat dose again after 2 weeks

Females of reproductive age with night blindness or Bitot's spots: 5000-10,000 units/day; 10,000 units/day maximum or ≤25,000 units once weekly for ≥4 weeks

 

Pediatric

Dosage Forms

capsule

  • 7,500 U
  • 8,000 U
  • 10,000 U
  • 25,000 U

injectable solution

  • 50,000 U/mL

tablet

  • 10,000 U
  • 15,000 U

RDA

0-6 months: 400 mcg/day RAE (1333 U/day)

6-12 months: 500 mcg/day RAE (1666 U/day)

1-3 years: 300 mcg/day RAE (1000 U/day)

3-8 years: 400 mcg/day RAE (1333 U/day)

8-13 years: 600 mcg/day RAE (2000 U/day)

13-18 years: 900 mcg/day RAE (3000 U/day)

Upper Intake Levels

0-3 years: 600/day mcg RAE (2000 U/day)

3-8 years: 900/day mcg RAE (3000 U/day)

8-13 years: 1700 mcg/day RAE (5667 U/day)

13-18 years: 2800 mcg/day RAE (9333 U/day)

13-18 years pregnant: 2800 mcg/day RAE (9333 U/day)

13-18 years breastfeeding: 2800 mcg/day RAE (9333 U/day)

Deficiency

Use IM route when oral administraiton is not possible or in malabsorption syndrome

Infants: 7500-15000 units/day for 10 days

1-8 years: 17,500-35,000 units/day for 10 days

>8 years

  • Malabsorption or oral administration not feasible: 100,000 U/day IM for 3 days; then 50,000 U/day for 2 weeks; follow with oral therapy.
  • Oral therapy: Take oral therapeutic multivitamin containing 10,000-20,000 U/day vitamin A for 2 months
  • Deficiency prophylaxis: 10,000-50,000 U PO qDay

Xerophthalmia

<6 months: 50,000 units qDay for 2 days; repeat once with single dose after 2 weeks

6-12 months: 100,000 units qDay for 2 days; repeat with single dose after 2 weeks

>1 year except females of reproductive age: 200,000 units qDay for 2 days; repeat with single dose after 2 weeks

Females of reproductive age with night blindness or Bitot's spots: 5000-10,000 units/day; 10,000 units/day maximum or ≤25,000 units once weekly for ≥4 weeks

Drug contraindications

pregnancy

Alerts

Cautions

Use caution if dose >25,000 units/day (monitor closely)

Evaluate additional vitamin deficiencies if diagnosis of vitamin deficiency occurs (single vitamin A deficiency rare)

Caution in renal impairment (toxicity reported)

Monitor prolonged administration over 25,000 units/day; take into account vitamin intake from other dietary and supplement sources

Efficacy of large systemic doses of 100,000 to 300,000 units/day vitamin A for the treatment of acne not established

Points of recommendation

Never take more than the recommended dose of vitamin A. Avoid taking more than one vitamin product at the same time unless your doctor tells you to. Taking similar vitamin products together can result in a vitamin overdose or serious side effects.

An overdose of vitamin A can cause serious or life-threatening side effects.

Do not take vitamin A without medical advice if you are pregnant. Vitamin A can cause birth defects if taken in large doses.

Before taking vitamin A, tell your doctor about all other medicines you use.


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