Piroxicam-induced photosensitivity. In vivo and in vitro studies of its photosensitizing potential.

A 36-year-old woman developed a photolocalized erythematous papulovesicular eruption while taking piroxicam. Histologic study revealed a superficial and deep spongiotic dermatitis. Phototesting with ultraviolet B (UVB) and ultraviolet A (UVA) was abnormal at the time the patient was seen and after oral challenge with the drug for 5 days. A modified lymphocyte transformation test was positive. The photosensitizing potential of the drug was evaluated in vivo and in vitro. In vivo studies consisted of phototesting twelve medical students before and after intake of piroxicam during 5 consecutive days. No lowering of the minimal erythema dose (MED) values or abnormal reactions to UV and visible light were observed in these students. In vitro studies by the Candida plate method and by photohemolysis showed negative results. Our studies suggest a systemic photoallergy mechanism requiring wavelengths in the UVA range for the reaction. This drug should be avoided in patients receiving photochemotherapy.