Retinoic acid (RA) is a metabolite of vitamin A (retinol). It promotes growth and development, controls anterior/posterior patterning in early embryonic developmental stages and is necessary for spermatogenesis in humans.

Retinoic acid activates the RAR retinoic acid receptors and RXR retinoid X receptors. These are nuclear hormone receptors.

Retinoic acid analogues are used in oncology and dermatology. Because of the importance of RA in differentiation and fetal development these drugs are considered potential teratogens, which may cause fetal harm if significant absorption occurs in a woman who is pregnant.

First generation retinoids:

All-trans RA (ATRA, tretinoin), is the most abundant naturally occurring RA isoform. It is used to induce remission in acute promyelocytic leukaemia patients.

9-cis-RA (alitretinoin) is a naturally occurring endogenous retinoid used topically to treat severe chronic hand eczema refractory to potent topical corticosteroids. May be used in some countries to inhibit the growth of Kaposi’s sarcoma.

13-cis RA (isotretinoin) is primarily used to treat cystic acne, either topically or by mouth (under expert supervision).

Second generation retinoids:

Etretinate, was used to treat severe psoriasis, but was withdrawn from many markets due to the high risk of birth defects.

Acitretin, a metabolite of etretinate is used to treat severe extensive psoriasis resistant to other forms of therapy, palmoplantar pustular psoriasis, severe congenital ichthyosis and severe keratosis follicularis (Darier’s disease).

Third generation retinoids:

Tazarotene is used to treat mild to moderate plaque psoriasis affecting up to 10% of the skin area.

Bexarotene is used to cause regression of cutaneous T-cell lymphoma.

Adapalene is used to treat mild to moderate acne vulgaris.