Retinoids and phototherapy for psoriasis.

Retinoids are the most widely used agents for systemic treatment of psoriasis; as structural and functional analogs of vitamin A, they are involved in the regulation of several biologic functions. Acitretin is the oral retinoid currently used, alone or in combination with other treatments, for plaque type, erythrodermic, and pustular psoriasis. Due to its high teratogenic effect, therapeutic contraception is required for women taking the drug. Narrowband ultraviolet B (nbUVB, 311 +/- 2 nm) is effective for guttate and plaque-type psoriasis. At the molecular level, UV light acts (1) directly (type I reaction) inducing the formation of pyrimidine dimers that, in turn, cause a transient cellular growth arrest; and (2) indirectly (type II reaction) through the generation of reactive oxygen species that act on key molecules such as lipids (in particular lipid membranes), proteins, and nucleic acids. Several studies show that UV rays can cause a transient decrease in DNA, RNA, and protein synthesis. These events are accompanied by a temporary normalization of cell kinetics of psoriatic keratinocytes. Phototherapy is carried out 3 times a week alone or in combination with topical treatments and/or acitretin. Several studies have confirmed that oral retinoids together with nbUVB (ReUVB) reduce the recovery time and also the doses of both acitretin and nbUVB. The regimen is carried out treating the patient with acitretin alone (0.5 mg/kg bw) for 2 weeks, then the dose of acitretin is reduced to 0.3 mg/kg bw, and the nbUVB is added 3 times a week until complete resolution of disease. As retinoids exert an anticarcinogenic effect, the ReUVB regimen could lower skin cancer risk resulting from longterm UVB therapy.