Primaquine is primarily used to prevent relapse of malaria due to Plasmodium vivax and Plasmodium ovale. It eliminates hypnozoites, the dormant liver form of the parasite, after the organisms have been cleared from the bloodstream. If primaquine is not administered to patients with proven P. vivax or P. ovale infection, a very high likelihood of relapse exists for weeks or months. Use in combination with quinine or chloroquine each of which is very effective at clearing P. vivax from blood, improves outcomes; they appear to also potentiate the action of primaquine. As of 2016, the US Centers for Disease Control and Prevention recommended the use of primaquine for primary prophylaxis prior to travel to areas with a high incidence of P. vivax, and for terminal prophylaxis after travel. A single dose of primaquine has rapid and potent ability to kill gametocytes of P. falciparum and P. vivax in blood; it also kills asexual trophozoites of P. vivax in blood, but not of P. falciparum. Because of its action against gametocytes, the WHO recommends it for use in reducing transmission to control P. falciparum infections.
''Pneumocystis'' pneumonia
Primaquine is also used in the treatment of Pneumocystis pneumonia, a fungal infection commonly occurring in people with AIDS and, more rarely, in those taking immunosuppressive drugs. To treat PCP effectively, it is usually combined with clindamycin.
Special populations
Primaquine has not been studied extensively in people 65 and older so it is not known if dosing should be adjusted for this population. Primaquine should not be administered to anyone with G6PD deficiency because a severe reaction can occur, resulting in hemolytic anemia. However, the WHO has recommended that a single dose of primaquine is safe to give even in individuals with G6PD deficiency, for the purpose of preventing transmission of P. falciparum malaria. Primaquine is contraindicated in pregnancy, because the glucose-6-phosphate dehydrogenase status of the fetus would be unknown. Primaquine overdose can cause a dangerous reduction in various blood cell counts, and therefore should be avoided in people at risk for agranulocytosis, which include people with conditions such as rheumatoid arthritis and lupus erythematosus, and those taking concurrent medications that also decrease blood cell counts.
Adverse reactions
Common side effects of primaquine administration include nausea, vomiting, and stomach cramps. In persons with cytochrome b5 reductase deficiency, primaquine causes methemoglobinemia, a condition in which the blood carries less oxygen that it does normally. Overdosing can reduce the number of function of various kinds of blood cells, including loss of red blood cells, methemoglobinemia, and loss of white blood cells. Persons with glucose-6-phosphate dehydrogenase deficiency may develop hemolytic anemia from primaquine.
Pharmacology
Mechanism of action
Primaquine is lethal to P. vivax and P. ovale in the liver stage, and also to P. vivax in the blood stage through its ability to do oxidative damage to the cell. However, the exact mechanism of action is not fully understood.
Pharmacokinetics
Primaquine is well-absorbed in the gut and extensively distributed in the body without accumulating in red blood cells. Administration of primaquine with food or grapefruit juice increases its oral bioavailibity. In blood, about 20% of circulating primaquine is protein-bound, with preferential binding to the acute phase proteinorosomucoid. With a half-life on the order of 6 hours, it is quickly metabolized by liver enzymes to carboxyprimaquine, which does not have anti-malarial activity. Renal excretion of the parent drug is less than 4%.
It is on the World Health Organization's List of Essential Medicines, the safest and most effective medicines needed in a health system. It is a generic drug and is available under many brand names worldwide, including Jasoprim, Malirid, Neo-Quipenyl, Pimaquin, Pmq, Primachina, Primacin, Primaquina, Primaquine, Primaquine diphosphate, Primaquine Phosphate, and Remaquin.
