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Primaquine
General information
The 8-aminoquinolines were the first synthetic antimalarial drugs to be introduced into medicine. Pamaquine (Plasmochin) was the first to be marketed in 1926, but primaquine proved to have the highest chemotherapeutic index of the many compounds tested.
Primaquine is rapidly absorbed, extensively distributed, and predominantly cleared by non-renal elimination. Its principal metabolite is carboxyprimaquine. While primaquine itself is rapidly eliminated from the plasma, the drug is effective when given once daily or even once weekly [ ]. The pharmacokinetics in children, pregnant women, and patients with renal or hepatic dysfunction are unknown.
Primaquine is mainly used to eradicate the exoerythrocytic stages of Plasmodium vivax and Plasmodium ovale , which if untreated cause late relapse [ ]. Primaquine resistance of P . vivax has been reported [ ].
Drug studies
Observational studies
Primaquine base 0.5 mg/kg/day in the prophylaxis of Plasmodium falciparum and P . vivax malaria for a year did not cause noteworthy adverse effects. General complaints were less than in the placebo group but about the same as in those treated with chloroquine. None of the volunteers (smokers or non-smokers) had a methemoglobin concentration greater than 13% [ ].
A randomized, placebo-controlled trial of supervised malaria prophylaxis with primaquine (30 mg/day for 20 weeks) in 97 non-immune adults with normal glucose-6-phosphate dehydrogenase (G6PD) concentrations in Papua New Guinea showed 93% protective efficacy of primaquine against malaria (95% CI = 71, 98%) [ ]. The most common adverse events were headache, abdominal pain, cough, and nausea, but these were not more frequent than with placebo. Transient rises in methemoglobin concentrations (mean 3.4% on the last day of prophylaxis, resolving by day 18) were asymptomatic.
Supervised treatment of P . vivax malaria with chloroquine (600 mg on day 1, 450 mg on days 2 and 3) and primaquine (15 mg/day for 14 days) has been studied in 50 patients in a non-endemic area of Brazil in a prospective open trial [ ]. G6PD status was not checked. The relapse-free cure rate at 6 months was 86%. There were no important adverse events. Risk factors for relapse included lower doses of primaquine. In patients over 60 kg in weight, the dose of primaquine can fall short of recommendations (0.25–0.3 mg/kg/day), and this can contribute to the risk of relapse.
Combination therapy
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