Table 3

K_i values for rosiglitazone, pioglitazone, and troglitazone against drug oxidation activities catalyzed by human hepatic microsomes

Isoform	Troglitazone	Rosiglitazone	Pioglitazone
	K _{i (μM)}
CYP2C8	2.59	5.59	1.69
CYP2C9	0.63	29.9	32.1
CYP2C19	10.2	N.D.	N.D.
CYP2D6	N.D.	29.5	N.D.
CYP3A4	1.6	36.3	11.8

Incubations were conducted with pooled microsomes (n = 15) under the conditions outlined under Materials and Methods. The substrate probes were used at 0.2 to 3 times the in vitro K_m values. Inhibitor concentrations were chosen based on the results from the IC₅₀ determinations (Table 2). A Micromass Quattro II or an LC tandem quadrupole mass spectrometer was used to monitor ions of the respective P450 marker metabolites.

N.D., not determined.