Bullous photoreaction to nalidixic acid

Curtaneous blisters developed after exposure to the sun in two women who were taking nalidixic acid. Blisters continued to appear even after therapy was discontinued and there was no further exposure to the sun. Phototesting showed abnormal sensitivity to both short and long wavelength ultraviolet spectra in one patient. The low incidence of this phenomenon suggests a photoallergic mechanism, but features of both photoallergy and phototoxicity are present.