Tafenoquine versus primaquine to prevent relapse of Plasmodium vivax malaria

To the Editor: Cytochrome P-450 2D6 (CYP2D6) screening has been used to improve the safety and efficacy of primaquine to prevent the clinical relapse of Plasmodium vivax malaria on the recommendation of the Centers for Disease Control and Prevention.1 Tafenoquine, a primaquine analogue, requires CYP2D6-mediated metabolic activation for antimalarial efficacy.2 In the trial by Llanos-Cuentas et al. (Jan. 17 issue)3 on the prevention of relapse of P. vivax malaria, we note that the reported percentages of patients in whom treatment with either primaquine or tafenoquine had failed were similar to percentages of predicted CYP2D6 reduced-function phenotypes in comparable geographic or . . .