Psoralens are furocoumarins that are used in combination with long wave ultraviolet light (UVA) to treat proliferative skin diseases. Important psoralen derivatives include bergapten, xanthotoxin and angelicin. Psoralens for medical purposes are obtained synthetically, but they are naturally occurring substances in a variety of plants – parsley, parsnip, celery and citrus fruits.
Simultaneous use of photosensitizers – psoralens and ultraviolet light with length 320 – 4 20 nm is used to cure different skin diseases – this method is called photochemotherapy, or PUVA. Psoralens are type I pho-tosensitizers – they produce a chemical reaction in the DNA molecule when exposed to UVA rays and are oxygen-independent.
In most cases of photochemotherapy the psoralen used is xanthotoxin, contained in the patent medicine Methoxalen, Oxoralen, Puvalen, etc. The medicine is resorbed fast by the skin and its highest concentration is in the first 2 – 4 hours. After that a part is disintegrated in the liver and the rest is excreted with the urine. The medicine is applied as a 0.15% solution of ethyl and isopropyl alcohol or in the form of tablets. The pa-tient is exposed to UVA rays one hour after spreading the solution or two hours after the tablet intake.
Psoralens are mainly used to treat psoriasis – genetically determined disease, characterized by patches of abnormal skin – papulo-squamosus dermatosis. PUVA therapy is also used to treat alopecia, cutaneous lymphomas – such as folliculotropic mycosis fungoides, vitiligo and atopic dermatitis. Side effects include itching, erythema, blisters, and skin cancers, caused by the cancerogenic effect of the UVA rays.
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