Nalidixic acid-induced photodermatitis after minimal sun exposure.

More than 30 cases of bullous photodermatitis have already been associated with the administration of nalidixic acid. This reaction is reported in a 57-year-old woman whose sun exposure was minimal. Nalidixic acid-induced photoreactions generally occur in females; they affect mainly the dorsal surfaces of the hands, feet, and legs, and usually do not involve the face. Blistering is always reported, and erythema is common. Dosage regimen and duration of treatment have little influence on the onset and severity of the reaction, which is probably of allergic nature. Its duration may be long, from three to six weeks, reexposure to the sun may trigger the reappearance of blistering for several months, even in the absence of a drug rechallenge.