TABLE 4

Bupropion glucuronidation kinetics^a

Substrate	K_m or S₅₀ (µM)	V_max	Cl_int^{^d} or Cl_max^{^e}
	μM	pmol/min/mg	µl/min/mg
(S,S)-hydroxybupropion glucuronide^a	172 ± 38.9	739 ± 59.6	4.31
(R,R)-hydroxybupropion glucuronide^a	488 ± 98.3	5550 ± 507	11.4
(1R,2R)-hydrobupropion glucuronide^{^b}	343 ± 37.5	3290 ± 269	7.7
(1S,2S)-hydrobupropion glucuronide^{^b}	248 ± 27.1	358 ± 25.5	1.1
EGLUC1^{^c}	373 ± 63.0	1740 ± 212	3.1
EGLUC2^{^c}	360 ± 55.2	2280 ± 241	3.8

Values represent the parameter estimate ± S.E. obtained by fitting the Michaelis-Menten^a (hydroxybupropion) or Hill.
↵^b Glucuronide 1 and glucuronide 2 denoted based on retention times in Figs. 1–3 and outlined in Table 2. Erythro-hydrobupropion glucuronide (EGLUC).
↵^c (threo- and erythro-hydrobupropion) equation to [substrate] versus metabolite formation velocity using Phoenix WinNonlin (version 6.4).
↵^d Intrinsic clearance (Cl_int), calculated as the ratio of V_max to K_m.
↵^e Maximal clearance (Cl_max), calculated as the ratio of V_max × (h − 1) to S₅₀ + h(h − 1)^1/h.