Within-host modelling of primaquine-induced haemolysis in hemizygote glucose-6-phosphate dehydrogenase deficient healthy volunteers

Primaquine is the only widely available drug to prevent relapses of Plasmodium vivax malaria. Primaquine is underused because of concerns over oxidant haemolysis in glucose-6-phosphate dehydrogenase (G6PD) deficiency. A pharmacometric trial showed that ascending-dose radical cure primaquine regimens causing ‘slow burn’ haemolysis were safe in G6PD deficient male volunteers. We developed and calibrated a within-host model of primaquine haemolysis in G6PD deficiency, using detailed serial haemoglobin and reticulocyte count data from 23 hemizygote deficient volunteers given ascending-dose primaquine (1,523 individual measurements over 656 unique timepoints). We estimate that primaquine doses of ∼0.75mg base/kg reduce the circulating lifespan of deficient erythrocytes by ∼30 days in individuals with common Southeast Asian G6PD variants. We predict that 5mg/kg primaquine total dose can be administered safely to G6PD deficient individuals over 14 days with expected haemoglobin drops of 18 to 43% (2.7 to 6.5g/dL drop from a baseline of 15g/dL).