The major metabolites from CYP-2D6-mediated pathway were 2-, 3-, and 4-hydroxyprimaquine, 5,6-orthoquinone product from 5-hydroxyprimaquine and PQ alcohol (as earlier reported) . The formation of 2-hydroxyprimaquine and the 5,6-orthoquinone predominated with (+)-PQ, while the 3-hydroxy- and 4-hydroxyprimaquine were formed more from the (−)-PQ. Quantitatively, 2-hydroxyprimaquine was four times more abundant from (+)-PQ than from (−)-PQ. Although the concentration of 2-hydroxyprimaquine peaked at 20 min with all substrates, 50 % of the peak concentration was already achieved by 5 min. CQ and QN completely suppressed the initial metabolite surge, with some metabolite appearing after an initial lag time (Fig. 2).