In vitro metabolism of sparteine by human liver: competitive inhibition by debrisoquine

Population data indicate that the genetic control is the same for the oxidation of sparteine and debrisoquine, although whether the level of control is regulatory or enzymatic is not clear. Therefore, the influence of debrisoquine on the rates of in vitro formation of the two dehydrogenated metabolites of sparteine in the 9000 x g supernatant fractions of human liver was examined. The interaction of these two drugs was competitive, indicating that the same form of cytochrome P450 is responsible for their biotransformation. Antipyrine at concentrations as high as 4 mM had no effect on sparteine oxidation.