Table 1.

Recommended in vitro probe substrates and inhibitors for CYPs.

	Substrates		Inhibitors
CYP	‘Preferred’	‘Acceptable’	‘Preferred’	‘Acceptable’
1A2	Ethoxyresorufin	Caffeine	Furafylline	α-naphthoflavone
	Phenacetin	(low turnover)		(but can also activate and inhibit CYP3A4)
		Theophylline
		(low turnover)
		Acetanilide
		(mostly applied in hepatocytes)
		Methoxyresorufin
2A6	Coumarin			Coumarin (but high turnover)
2B6	S-Mephenytoin (N-desmethyl	Bupropion (availability of metabolite standards?)		Sertraline (but also inhibits CYP2D6)
2C8	Paclitaxel		(‘glitazones’ – availability of standards?)
	(availability of standards?)
2C9	S-Warfarin	Tolbutamide	Sulphaphenazole
		Diclofenac	(low turnover)
2C19	S-Mephenytoin (4-hydroxy metabolite)			Ticlopidine (but also inhibits CYP2D6)
	Omeprazole			Nootkatone (but also inhibits CYP2A6)
2D6	Bufuralol	Metoprolol	Quinidine
	Dextromethorphan	Debrisoquine
		Codeine (all with no problems, but less commonly used)
2E1	Chlorzoxazone	4-nitrophenol		4-methyl pyrazole
		Lauric acid
3A4	Midazolam	Nifedipine	Ketoconazole	Cyclosporin
	Testosterone (strongly recommended to use at least two structurally unrelated substrates)	Felodipine Cyclosporin	(but recent evidence indicates that it is also a potent inhibitor of CYP2C8)
		Terfenadine
		Erythromycin	Troleandomycin
		Simvastatin