CQ and QN had no effect on the primary amine oxidation products (CPQ or PQ alcohol or the cyclized aldehyde) (Fig. 6). However, surprisingly they did inhibit substantially the appearance of the glucuronides of CPQ and PQ alcohol. They also inhibited the appearance of the m/z 257 metabolite with a similar pattern, suggesting that it may be derived from the CPQ conjugate. The formation of 4-OH-PQ and the quinone-imine (m/z 274) were essentially completely suppressed, and the m/z 422 metabolite was very strongly suppressed (90–95 %) by both CQ and QN. The apparent quinone-imine of CPQ (m/z 289) was partially suppressed, but more prominently by CQ than QN. The carbamoyl glucuronide of PQ (m/z 480) was not affected.Fig. 6The inhibitory effects of chloroquine and quinine on the formation of metabolites from primaquine and its (+)- and (−)-enantiomers after one-hour incubation in human hepatocytes. Each point represents mean of 4 determinations. The major metabolites were carboxyprimaquine [predominantly from (−)-PQ], carbamoyl primaquine glucuronide [exclusively from (+)-PQ] and glycosylated primaquine (formed from both enantiomers). The inhibitory effect of chloroquine and quinine on the formation of carboxyprimaquine and carbamoyl primaquine glucuronide was mild