TABLE 4

IC₅₀ values for inhibition of cytochrome P450 enzymes by rhinacanthin-C

Enzyme	Substrate	Metabolite	IC₅₀ (µM)^{^a}
CYP1A2	Phenacetin	Acetaminophen	>50
CYP2A6	Coumarin	7-Hydroxycoumarin	>50
CYP2B6	Bupropion	Hydroxybupropion	>50
CYP2C8	Amodiaquine	N-desethylamodiaquine	4.45 ± 0.44
CYP2C9	Tolbutamide	Hydroxytolbutamide	1.57 ± 0.22
CYP2C19	(S)-mephenytoin	(±)-4′Hydroxymephenytoin	29.40 ± 4.16
CYP2D6	Dextromethorphan	dextrophan	>50
CYP2E1	Chlorzoxazone	6-Hydroxychlorzoxazone	>50
CYP3A4/5^{^b}	Midazolam	1′-Hydroxymidazolam	53.00 ± 4.22
	Testosterone	6β-Hydroxytestosterone	81.20 ± 6.42

↵^a IC₅₀ values are expressed as the mean ± S.E. of three independent experiments.
↵^b Tested at the concentration range of 1–100 µM.