Table 5

Influence of quinidine on warfarin metabolism in human liver microsomes^5-a

Quinidine	10-Hydroxylation ofR-Warfarin		4′-Hydroxylation ofS-Warfarin
Quinidine	K_m 5-b	V_max 5-b	K_m 5-b	V_max 5-b
μM	mM	pmol/min/mg	mM	pmol/min/mg
0	0.24 ± 0.04	133 ± 12	0.12 ± 0.02	13 ± 1
1	0.25 ± 0.07	147 ± 17	0.13 ± 0.02	16 ± 1
5	0.26 ± 0.05	282 ± 22	0.14 ± 0.04	23 ± 2
10	0.22 ± 0.04	359 ± 27	0.13 ± 0.03	27 ± 2
25	0.23 ± 0.04	499 ± 34	0.12 ± 0.02	33 ± 2
50	0.21 ± 0.03	568 ± 31	0.11 ± 0.02	34 ± 2
100	0.20 ± 0.03	658 ± 39	0.13 ± 0.02	37 ± 2
200	0.22 ± 0.04	654 ± 44	0.13 ± 0.01	34 ± 1

↵5-a Warfarin in methanol and quinidine in distilled water were added to human liver microsomes suspended in phosphate buffer (0.1 M, pH 7.4) containing EDTA.
↵5-b The kinetic parameters were determined based on the Michaelis-Menten equation. Data are presented as mean ± S.E.