The possibility of drug toxicity (including QT interval (QTc) prolongation and retinal toxicity) should be considered prior to using hydroxychloroquine, particularly in individuals who may be more susceptible to these effects including epilepsy, porphyria, myasthenia gravis, and retinal pathology—glucose-6-phosphate dehydrogenase (G6PD) deficiency [47,49]. Here, G6PD is linked to porphyria.