Primaquine is a potent antimalarial medication indicated for the radical cure of malaria caused by Plasmodium vivax (P. vivax) and Plasmodium ovale (P. ovale) species (1, 2). Malaria is a blood borne infection caused by infection of Plasmodium parasites that is spread by mosquitos. The P. vivax and P. ovale species present a particular challenge to treat because the parasitic life cycle includes a dormant, liver-specific stage that is not susceptible to other antimalarial medications. Thus, primaquine is often used with other therapies such as chloroquine or artemisinin-based medicines that target the reproductive, active forms of the parasite. Primaquine is also used to prevent transmission of malaria caused by Plasmodium falciparum (P. falciparum) species. A single, low dose (SLD) of primaquine has gametocidal activity, which does not cure the individual but does provide malaria transmission control.
Primaquine is a pro-drug that must be activated by the cytochrome P450 (CYP) enzyme system. Metabolism by the cytochrome P450 member 2D6 (CYP2D6) and cytochrome P450 nicotinamide adenine dinucleotide phosphate (NADPH):oxidoreductase (CPR) generates 2 hydroxylated active metabolites that generate hydrogen peroxide (H2O2). This causes significant oxidative stress to the malarial parasite and the host human cells. Individuals who are glucose-6-phosphate dehydrogenase (G6PD) deficient are particularly susceptible to oxidative stress and may experience acute hemolytic anemia (AHA). Before starting a course of primaquine, individuals should be tested for G6PD deficiency to ensure safe administration (1, 2). According to the FDA-approved drug label, individuals with severe G6PD deficiency should not take primaquine (Table 1) (1).
The World Health Organization (WHO) recommends that individuals with G6PD deficiency should be treated with a modified course of primaquine therapy. The recommended course for individuals with G6PD deficiency is a single dose once per week for 8 weeks, while the standard course is daily administration for 14 days (Table 2) (2). The Clinical Pharmacogenetics Implementation Consortium (CPIC) reports that the risk of adverse effects of primaquine therapy for G6PD-deficient individuals is dose-dependent, with the SLD regimen presenting the least risk (Table 3) (3).
Primaquine is contraindicated during pregnancy and is not recommended for breastfeeding individuals when the G6PD status of the baby is unknown (1, 2). Primaquine is not approved for individuals under 6 months of age. Individuals with acute illness that are prone to granulocytopenia or individuals taking another hemolytic medication are also contraindicated from taking primaquine. (1)