Vitamin A

Oleovitamin A, Retinol

Mechanism :

It is a beta-carotene, fat-soluble vitamin. It is used in the production of the eye pigment (rhodopsin) necessary for vision and for maintenance of the normal structure and texture of skin. The principal and most active substance is all-trans retinol (vitamin A alcohol). Derivatives of vitamin A such as tretinoin (all trans-retinoic acid) and isotretinoin (13-cis-retinoic acid) are used in the treatment of acne and certain other skin disorders.

Indication :

• Night blindness
• Vitamin A deficiency
• Malabsorptive states
• Cholestasis
• Ichthyosis

Contraindications :

Hypervitaminosis A; hypersensitivity to vitamin A or any component of a vitamin A containing pharmaceutical preparation.

Dosing :

RDA:

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

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

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

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

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

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

Treatment of Vitamin A Deficiency:

Infants: Initially, 7500-15,000 units IM daily for 10 days, follow with 5000-10,000 units orally daily for 2 months.

1-8 years of age: Initially, 17,500-35,000 units IM daily for 10 days, follow with 5000-10,000 units orally daily for 2 months.

>8 years of age: 100,000 units IM daily for 3 days, then 50,000 units IM daily for 2 weeks. Follow with 10,000-20,000 units of vitamin A orally daily for 2 months.

Xerophthalmia: Oral

Infants <6 months of age: Initially, 50,000 units daily for 2 days; repeat with 50,000 units at least 2 weeks later (total of 3 doses).

Children 6-12 months of age: Initially, 100,000 units daily for 2 days, then 100,000 units at least 2 weeks later (total of 3 doses).

Children >12 months of age: Initially, 200,000 units daily for 2 days, then 200,000 units at least 2 weeks later (total of 3 doses).

Prevention of Deficiency:

Children living in underdeveloped countries where vitamin A deficiency resulting in keratomalacia and blindness is common: 50,000-200,000 units every 4-6 months have been given.

Children with Measles:

Oral or IM: 50,000 units once daily for 2 days; administer a third dose 2-4 weeks later if clinical manifestations of vitamin deficiency are present.

Cholestasis:

10,000-12000 U PO daily.

Adverse Effect :

Acute toxicity seen in overdoses include-increased intracranial pressure, headache, irritability, drowsiness, dizziness, lethargy, vomiting, diarrhea, bulging of fontanels in infants, diplopia, papilledema.

Chronic: Excessive ingestion may produce symptoms of pseudotumor cerebri, anorexia, weakness, arthralgias, bone pain, bone demineralization, dry skin, cracked lips, brittle nails, hair loss, splenomegaly, hepatomegaly, hypoplastic anemia, leukopenia, optic neuropathy, and blindness.

Interaction :

Mineral Oil: Excessive use of mineral oil as a laxative may reduce the utilization of the provitamin by carrying away large amounts in the faeces.
Cholestyramine and neomycin: May affect drug absorption.
Isotretinoin: Vitamin A should not be used concurrently with isotretinoin since toxic effects may be additive.
Contraceptives: Women on oral contraceptives have shown a significant increase in plasma vitamin A concentrations.

Hepatic Dose :