Hydroxychloroquine Therapy and G6PD Genotype

Excerpt

Hydroxychloroquine, which is closely related to chloroquine, can be used for the prevention and treatment of some forms of malaria and rheumatic conditions such as systemic lupus erythematosus (SLE) and rheumatoid arthritis. Malaria is an infection caused by the Plasmodium parasite, transmitted via mosquito bites. Hydroxychloroquine sulfate is indicated for the prevention and treatment of uncomplicated malaria due to sensitive strains of Plasmodium falciparum (P. falciparum), Plasmodium vivax (P. vivax), Plasmodium malariae (P. malariae), Plasmodium ovale (P. ovale), and Plasmodium knowlesi (P. knowlesi) by both the US Centers for Disease Control (CDC) and World Health Organization (WHO) (1, 2). Resistance to chloroquine and hydroxychloroquine has been reported in Plasmodium species, thus hydroxychloroquine therapy is not recommended if the infection arose in a region with known resistance. Most P. falciparum infections are resistant to the 4-aminoquinolines (chloroquine and hydroxychloroquine), and as such these drugs are no longer used widely for these infections. Hydroxychloroquine must be co-administered with an 8-aminoquinoline compound for the radical cure of P. vivax or P. ovale infection to eliminate the hypnozoite forms of these parasites. (3) Additionally, hydroxychloroquine is indicated for the treatment of many rheumatoid conditions in adults, including chronic discoid lupus erythematosus, systemic lupus erythematosus, as well as acute and chronic rheumatoid arthritis. Hydroxychloroquine has also been used in an off-label capacity for the management of Sjögren syndrome (4).

Hydroxychloroquine accumulates in cellular acidic compartments such as the parasitic food vacuole and mammalian lysosomes, leading to alkalinization of these structures. Among antimalarial medications, hydroxychloroquine is less likely than other medicines to cause hemolysis in glucose-6-phosphate dehydrogenase (G6PD)-deficient individuals; however, the U.S. FDA-approved drug label states there is still a risk of acute hemolytic anemia (AHA) (Table 1) (3). In contrast, the Clinical Pharmacogenetics Implementation Consortium (CPIC) performed a systematic review of the available clinical literature and found low-to-no risk of AHA for individuals with G6PD deficiency who take hydroxychloroquine (5). It should be noted that G6PD deficiency has a range of severity; CPIC advises caution for all medications when used by an individual with a severe G6PD deficiency with chronic non-spherocytic hemolytic anemia (CNSHA) (Table 2) (5). Regardless of G6PD phenotype, chronic use of hydroxychloroquine can cause irreversible retinal damage and regular visual exams are recommended by the FDA (3).