Primaquine is an 8-aminoquinoline.
Primaquine has a broad spectrum of activity against all stages of the plasmodium development in humans but uniquely induce radical cure (anti-relapse therapy) of P. vivax and P. ovale malaria. It has activity against Pneumocystis (carinii) jiroveci.
Most of the antimalarial activity of primaquine is probably derived from hydroxylated metabolites which may become oxidised and initiate radical formation and reactive oxygen species.
Primaquine is rapidly and nearly completely absorbed after oral administration. Its elimination half-life is 5-7 hours. Primaquine is extensively metabolized and less than 2% of the dose is excreted unaltered into the urine.
The classical dosage regimen is once daily 15 mg for 14 days. However there are significant geographic differences in susceptibility to primaquine with respect to strains of P. vivax. Thus, dose recommendations are usually determined by the geographic source of the infection (Table 1).
A daily dose of 0.5 mg/kg primaquine, taken with breakfast and extended for one week after leaving the endemic area offers good prophylaxis against P. vivax and P. falciparum.
Primaquine is contraindicated in pregnancy. The fetus is relatively deficient in G6PD.
Primaquine can induce haemolysis but not all individuals are equally sensitive to this effect. A red cell defect, caused by deficiency of glucose-6-phosphate dehydrogenase (G6PD) is responsible for haemolysis in primaquine sensitive individuals. Primaquine may induce methaemoglobinaemia irrespective of the G6PD status of the patient.