Reduction of ferricytochrome C and oxidation of haemoglobin was used to examine redox properties of primaquine, metabolites and photodegradation products of the drug. The influence of oxygen radicals (O2·- and OH·) were studied by the addition of oxygen radical scavengers. Photodecomposition of primaquine (80 mW/cm2, xenon lamp, 290-800 nm) prior to dark-incubation resulted in a substantial accelerated drug-induced O2·- formation and haemoglobin oxidation. Formation of OH (dark reaction) could be detected after photochemical degradation of primaquine. In the presence of erythrocytes the formation of oxygen radicals induced by the photodecomposition products was even more pronounced. A high oxygen content in the medium during irradiation accelerated the photodecomposition-rate of primaquine. The metabolite 6-desmethyl primaquine was a more potent O2·- producer and haemoglobin oxidizer than primaquine (dark reactions). During irradiation (80 mW/cm2, 290-800 nm) primaquine formed more O2·- and produced a detectable level of OH· compared to the dark reactions.
Kristensen, S., Grinberg, L., & Tønnesen, H. H. (1997). Photoreactivity of biologically active compounds XI. Primaquine and metabolites as radical inducers. European Journal of Pharmaceutical Sciences, 5(3), 139–146. https://doi.org/10.1016/S0928-0987(97)00268-6