Anaphylaxis to 5-methoxypsoralen during photochemotherapy

Photochemotherapy is very effective for the treatment of skin diseases such as psoriasis, as well as for the prophylactic 'hardening' therapy of patients suffering from polymorphic light eruption. The photosensitizers most widely used for oral photochemotherapy are the furocoumarins 8-methoxypsoralen and 5-methoxypsoralen. Beside light-induced phototoxic reactions due to the photosensitizing activity of psoralens, side-effects after the oral intake of psoralens are nausea and vomiting, headaches, anxiety and sleeplessness. We report a rare case of anaphylaxis to 5-methoxypsoralen that developed during prophylactic 'hardening' therapy in a 36-year-old woman suffering from polymorphic light eruption. Anaphylaxis to 5-methoxypsoralen was established by placebo-controlled oral provocation tests.