Phototoxic properties of quinine and quinidine: two quinoline methanol isomers

Clinical photoreactions have been reported for quinine and quinidine after systemic and topical administration. We have investigated the phototoxic properties of these two quinoline methanol isomers in vitro using the Candida albicans inhibition test and photohemolysis, and in vivo with the mouse tail phototoxicity test. Both isomers were phototoxic in the hemolysis model, quinine being the more potent compound. In the Candida test only quinidine was phototoxically active. In the mouse tail model, measuring edema, the phototoxic activity of quinidine was comparatively low, causing a 7.3% wet weight increase of tail tissue at a dose of 150 mg/kg intraperitoneally of drug and 54 J/cm2 of UVA. In spite of its structural similarity to quinidine, quinine was not phototoxic in the mouse. These studies support the assumption, based on clinical data, that quinine photoreactions probably have a non-phototoxic mechanism. For quinidine, however, light-induced reactions based on phototoxicity can not be ruled out, since low-grade phototoxic properties were demonstrated in vivo.