Primaquine

Primaquine is an 8-aminoquinoline [quinoline = bicyclic N-containing aromatic structure consisting of a benzene ring with a pyridine ring]. It is inactive upon asexual blood forms. It does have an important, though only partial, causal prophylactic effect (on both P. falciparum and P. vivax), but only if it is taken 24-48 hours (max. 96 hours) after inoculation with sporozoites. It acts upon the exo-erythrocytic stages of the parasites (liver schizonts). The half-life is relatively short (4 hours). For causal prophylactic use a daily dose of 15-30 mg may be taken. These regimens are not, however, very popular and there has been little experience of them. Chemoprophylaxis with primaquine can be stopped 3 days after leaving a malarious area.

In cases of P. vivax or P. ovale malaria, hypnozoites still remain in the liver after therapy with chloroquine. These may be destroyed by primaquine. Generally 15 mg base per day is used for 14 days [26 mg primaquine biphosphate = 15 mg primaquine base]. This is contra-indicated in pregnant women and where there is a significant deficiency of G6PD (glucose-6-phosphate dehydrogenase), an enzyme in the red blood cells (risk of haemolysis). In significant G6PD-deficiency no primaquine is given, or 0.75 mg/kg once per week for 8 weeks or 30 mg once per week for 15 weeks. There are P. vivax strains (e.g. P. vivax Chesson) which are less sensitive (India, Southeast Asia) and here 22.5 mg is given per day for 21 days. This therapy is certainly sensible for those who are finally returning from the tropics or from a malaria region. Sometimes what is called terminal prophylaxis is used. Primaquine can sometimes cause nausea, especially high doses taken on an empty stomach. Nausea is much less common if primaquine is taken with food. Primaquine also acts on gametocytes and in some circumstances (e.g. refugee camps) may be given to reduce transmission. Older products which are structurally related to primaquine [8-aminoquinolines], such as pamaquine (Plasmoquine, Praequine), rhodoquine (Plasmocide), quinocide, pentaquine and isopentaquine are almost never used any more.

Mild methaemoglobinemia (usually <13%)>

Category: Medicine Notes