Phototoxicity from nalidixic acid: oxygen dependent photohemolysis.

Erythrocyte lysis photosensitized by nalidixic acid was investigated. This photohemolysis was found to be oxygen dependent. The effects of various antioxidants and hydroxyl radical scavengers on photohemolysis induced by nalidixic acid suggested a photo-oxidative step. In addition, using the oxygen quencher histidine and the deuterium oxide effect on the singlet oxygen lifetime we obtained evidence indicative of a photodynamic mechanism mediated by oxygen singlet and hydroxyl radicals. On the other hand, pre-irradiated nalidixic acid was not lytic to erythrocytes, yet photoproducts of nalidixic acid demonstrated a greater photohemolytic potential than nalidixic acid itself.