title: CYP2B6 mediates the in vitro hydroxylation of bupropion: potential drug interactions with other antidepressants.
abstract: The in vitro biotransformation of bupropion to hydroxybupropion was studied in human liver microsomes and microsomes containing heterologously expressed human cytochromes P450 (CYP). The mean (+/-S.E.) K(m) in four human liver microsomes was 89 (+/-14) microM. In microsomes containing cDNA-expressed CYPs, hydroxybupropion formation was mediated only by CYP2B6 at 50 microM bupropion (K(m) 85 microM). A CYP2B6 inhibitory antibody produced more than 95% inhibition of bupropion hydroxylation in four human livers. Bupropion hydroxylation activity at 250 microM was highly correlated with S-mephenytoin N-demethylation activity (yielding nirvanol), another CYP2B6-mediated reaction, in a panel of 32 human livers (r = 0.94). The CYP2B6 content of 12 human livers highly correlated with bupropion hydroxylation activity (r = 0.96). Thus bupropion hydroxylation is mediated almost exclusively by CYP2B6 and can serve as an index reaction reflecting activity of this isoform. IC(50) values for inhibition of a CYP2D6 index reaction (dextromethorphan O-demethylation) by bupropion and hydroxybupropion were 58 and 74 microM, respectively. This suggests a low inhibitory potency versus CYP2D6, the clinical importance of which is not established. Since bupropion is frequently coadministered with other antidepressants, IC(50) values (microM) for inhibition of bupropion hydroxylation were determined as follows: paroxetine (1.6), fluvoxamine (6.1), sertraline (3.2), desmethylsertraline (19.9), fluoxetine (59.5), norfluoxetine (4.2), and nefazodone (25.4). Bupropion hydroxylation was only weakly inhibited by venlafaxine, O-desmethylvenlafaxine, citalopram, and desmethylcitalopram. The inhibition of bupropion hydroxylation in vitro by a number of newer antidepressants suggests the potential for clinical drug interactions.
authors.affiliation: Department of Pharmacology and Experimental Therapeutics, Tufts University School of Medicine, and the Division of Clinical Pharmacology, New England Medical Center, Boston, Massachusetts, USA.
authors.forename: L M
authors.initials: LM
authors.lastname: Hesse
authors.forename: K
authors.initials: K
authors.lastname: Venkatakrishnan
authors.forename: M H
authors.initials: MH
authors.lastname: Court
authors.forename: L L
authors.initials: LL
authors.lastname: von Moltke
authors.forename: S X
authors.initials: SX
authors.lastname: Duan
authors.forename: R I
authors.initials: RI
authors.lastname: Shader
authors.forename: D J
authors.initials: DJ
authors.lastname: Greenblatt
mesh_terms: D000906:Antibodies / Q000494:pharmacology; D018687:Antidepressive Agents, Second-Generation / Q000378:metabolism* / Q000493:pharmacokinetics; D001189:Aryl Hydrocarbon Hydroxylases; D001711:Biotransformation; D016642:Bupropion / Q000378:metabolism* / Q000493:pharmacokinetics; D002851:Chromatography, High Pressure Liquid; D065702:Cytochrome P-450 CYP2B6; D003577:Cytochrome P-450 Enzyme System / Q000276:immunology / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D004347:Drug Interactions; D005473:Fluoxetine / Q000031:analogs & derivatives* / Q000494:pharmacology; D016666:Fluvoxamine / Q000494:pharmacology; D006801:Humans; D006900:Hydroxylation / Q000187:drug effects; D007527:Isoenzymes / Q000378:metabolism; D007700:Kinetics; D008862:Microsomes, Liver / Q000378:metabolism; D010089:Oxidoreductases, N-Demethylating / Q000276:immunology / Q000378:metabolism*; D017374:Paroxetine / Q000494:pharmacology; D010879:Piperazines; D020280:Sertraline / Q000031:analogs & derivatives* / Q000494:pharmacology; D014230:Triazoles / Q000494:pharmacology
chemical_list: D000906:Antibodies; D018687:Antidepressive Agents, Second-Generation; D007527:Isoenzymes; D010879:Piperazines; D014230:Triazoles; D005473:Fluoxetine; D016642:Bupropion; D017374:Paroxetine; C051752:nefazodone; D003577:Cytochrome P-450 Enzyme System; C065162:desmethylsertraline; D001189:Aryl Hydrocarbon Hydroxylases; C585599:CYP2B6 protein, human; D065702:Cytochrome P-450 CYP2B6; D010089:Oxidoreductases, N-Demethylating; C036139:norfluoxetine; D016666:Fluvoxamine; D020280:Sertraline