TABLE 2

Probe drug and activity used to measure microsomal P450 enzyme activity rate (pmol/mg protein/min) and interindividual variability therein

Liver microsomes were prepared and P450 enzyme activity rates were determined as described under Materials and Methods.

Enzyme	Probe Drug/Activity	Minimum	Maximum	Variability (-Fold)	Mean Activity Level	S.D.
	pmol/mg protein/min
CYP1A2	7-Ethoxyresorufin O-dealkylation	5.9	175	30	39	43
CYP2A6	Coumarin 7-hydroxylation	91.5	4000	44	958	1179
CYP2B6	S-Mephenytoin N-demethylation	13	1280	98	191	315
CYP2C8	Paclitaxel 6α-hydroxylation	37.4	2040	55	512	623
CYP2C9	Diclofenac 4′-hydroxylation	210	3530	17	1748	774
CYP2C19	S-Mephenytoin 4′-hydroxylation	2.69	344	128	94	89
CYP2D6	Dextromethorphan O-demethylation	85.5	870	10	392	170
CYP2E1	Chlorzoxazone 6-hydroxylation	358	4270	12	2057	974
CYP3A4/5	Testosterone 6β-hydroxylation	201	20,300	101	5081	6196