Medical Health Encyclopedia

Ultraviolet A (UVA) is the other main part of sunlight. The treatment using UVA requires a photosensitizing medication (usually psoralen) in combination with UVA radiation to be effective. Therefore the treatment is referred to as PUVA. This approach is very potent and is effective in more than 85% of patients that use it. However, it poses a higher risk for skin cancers than UVB.

PUVA treatments cause inflammation and redness in the skin to develop within two to three days after treatment. Such damage inhibits skin cell proliferation and reduces psoriasis plaque formation. PUVA employs a combination of a psoralen drug and ultraviolet A (UVA) radiation. Forms of psoralen include methoxsalen, 8-methoxypsoralen (8-MOP), or bergapten (5-MOP). The effectiveness of the treatment is based on a chemical reaction in the skin between the psoralen and light, which creates redness and inflammation that prevents the psoriasis disease process.

People should avoid this treatment if they are taking drugs or have conditions that cause them to be light sensitive. They should also take protective measures before, during, and after each treatment.

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Initial PUVA Treatment Phase. The initial phase typically follows these steps:

• Psoralen is typically taken by mouth in the form of 8-methoxypsoralen (e.g., Oxsoralen) 75 minutes to two hours before the treatment starts. Psoralen reaches the skin through the bloodstream, where it increases the skin's sensitivity to UVA radiation.
• Topical preparations of psoralen are alternatives to pills. They can be "painted on" or applied to the affected areas by soaking or bathing in a psoralen solution. PUVA-bath therapy may be especially useful for persistent psoriasis on the palms and soles or for patients with liver disease or who get severe nausea from taking the pill form. UVA should be administered within 15 minutes of these procedures.
• The patient then enters the "light box," a unit lined with ultraviolet lamps, in which patients typically stand in. Initial time is very short (seconds to several minutes) and then increases to 20 minutes or longer. The amount of time a person is exposed to UVA rays depends on the skin type, with the shortest times recommended for fair-skinned patients.
• Treatments may be repeated two or three times a week. They should never be performed more frequently than once every other day, since the full effects of the treatments are not evident for 48 hours.