RT Journal Article
SR Electronic
T1 Ethosuximide is Primarily Metabolized by CYP3A when Incubated with Isolated Rat Liver Microsomes
JF Drug Metabolism and Disposition
JO Drug Metab Dispos
FD American Society for Pharmacology and Experimental Therapeutics
SP 78
OP 82
VO 26
IS 1
A1 Jeffrey G. Sarver
A1 Kenneth A. Bachmann
A1 Daling Zhu
A1 Wieslaw A. Klis
YR 1998
UL http://dmd.aspetjournals.org/content/26/1/78.abstract
AB The cytochrome P450 (CYP) subfamily responsible for ethosuximide metabolism was investigated by HPLC assay of ethosuximide incubations with isolated rat liver microsomes from control rats and from rats treated with inducing agents to enrich hepatic microsomes in selected CYP isoforms. Inducing agents included β-naphthoflavone (BNF, CYP1A inducer), phenobarbital (PB, CYP2B/2C/3A), isoniazid (INH, CYP2E1), clotrimazole (CTZ, CYP3A), clofibrate (CLO, CYP4A), and an imidazole CTZ-analog known as CDD3543 (CYP3A). Incubations with BNF, INH, CTZ, and control microsomes showed significantly (p<0.05) more metabolite produced by CTZ microsomes vs. BNF, INH, and control microsomes at 10, 30, 60, and 120 min incubation. Ethosuximide metabolite levels generated by CTZ microsomes at 120 min were 36.5 times those of control microsomes. Correspondingly, ethosuximide concentrations were significantly (p<0.05) lower for incubations with the CTZ microsomes compared with BNF, INH, and control microsomes at 60 and 120 min. Sixty-minute incubations with all microsome groups exhibited significantly (p<0.05) higher metabolite formation rates (nmol/nmol CYP/min) for CTZ (11.8x control) and PB (9.6x control) microsomes vs. all other groups. Antibody inhibition experiments demonstrated ethosuximide metabolite levels for PB microsomes were not affected by CYP2B1 antibodies, whereas CYP3A2 antibodies reduced metabolite levels for both PB and CTZ microsomes by over 80%. These results indicate CYP3A is primarily responsible for ethosuximide metabolism in rats. The American Society for Pharmacology and Experimental Therapeutics