PQ was steadily depleted to varying degrees in the incubation mixtures with recombinant CYP2D6 such that by 2 h, 65, 50 and 72 % of the racemic, (+)- and (−)-PQ remained, respectively. Both CQ and QN suppressed this depletion with all three substrates such that more than 90 % of the substrates remained after 2 h (Fig. 2a–c).Fig. 2The influence of chloroquine and quinine on the CYP2D6-mediated depletion of racemic PQ (a) and its enantiomers (b, c); and formation of 2-hydroxyprimaquine from racemic PQ (d) and e, f over 2 h of incubation. Each point represents values: mean ± S.D. (n = 4)