Psoralens with ultraviolet A

This is a form of photochemotherapy. It combines the use of a psoralen e.g. the photosensitizing drug methoxsalen with ultraviolet A phototherapy (PUVA) in the range of 320 to 400 nm.

The proposed mechanisms of action of PUVA include:

• suppression of cell-mediated immunity
• suppression of cell proliferation by interference with DNA synthesis

PUVA is highly effective in the treatment of psoriasis with resolution of skin lesions in over 85% of patients after 20 to 30 treatments combining drug use and ultraviolet A irradiation.

• oral psoralen can cause nausea - patients must wear protective eyewear on the treatment days to prevent cataract formation
• topical PUVA - patients apply psoralen paint or gel to the skin or soak in a bath of psoralen solution prior to light exposure
  • does not require wearing eyewear or taking tablets
• there is a risk of nonmelanoma skin cancers associated with prolonged PUVA therapy
• PUVA therapy is often combined with other treatments such as retinoids and vitamin D analogues to reduce the number of exposures required for clearance

Reference:

1. Prescriber (2005); 16(8).
2. Wood AJ, (1995). Treatment of psoriasis, NEJM; 332 (9): 581-7.