Clinical indications for vitamin A

Although chemically related, retinoic acid and retinol have distinctly different therapeutic applications. Retinol and its carotenoid precursor are used as dietary supplements, whereas various forms of retinoic acid are useful in dermatology (Fig. 1).

Figure 1: Summary of actions of retinoids. Compounds in are available as dietary components or as pharmacologic agents.
1. Deficiency: Vitamin A, administered as retinol or retinyl esters, is used to treat patients who are deficient in the vitamin. Night blindness (nyctalopia) is one of the earliest signs of vitamin A deficiency. The visual threshold is increased, making it difficult to see in dim light. Prolonged deficiency leads to an irreversible loss in the number of visual cells. Severe deficiency leads to xerophthalmia, a pathologic dryness of the conjunctiva and cornea, caused, in part, by increased keratin synthesis. If untreated, xerophthalmia results in corneal ulceration and, ultimately, in blindness because of the formation of opaque scar tissue.
The condition is most commonly seen in children in developing tropical countries. Over 500,000 children worldwide are blinded each year by xerophthalmia caused by insufficient vitamin A in the diet.
2. Skin conditions: Dermatologic problems such as acne are effectively treated with retinoic acid or its derivatives (see Fig. 1). Mild cases of acne and skin aging are treated with tretinoin (all-trans retinoic acid).
Tretinoin is too toxic for systemic (oral) administration in treating skin conditions and is confined to topical application. [Note: Oral tretinoin is used in treating acute promyelocytic leukemia.] In patients with severe cystic acne unresponsive to conventional therapies, isotretinoin (13-cis retinoic acid) is administered orally. An oral synthetic retinoid is used to treat psoriasis.