IC50: 121 μM (CYP2D6)
Ki: 54 μM (CYP2D6)

CYP2D6 reveals the highest metabolic activity for the generation of 9-O-demethylEmetine, whereas this enzyme also shows a significant metabolic activity for the generation of Cephaeline. The IC ₅₀ s of Cephaeline against CYP2C9, CYP2D6 and CYP3A4 is over 1000, 121 and 1000 μM, respectively. Further experiments are performed to determine inhibition constants (K _i ) for Cephaeline on the CYP2D6 and CYP3A4 activities Graphic analysis of Dixon plots at various Cephaeline concentrations for each of the two CYP enzyme assays yield K _i s of 54 and 355 μM for CYP2D6 and CYP3A4, respectively.