The 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