title: Venlafaxine: in vitro inhibition of CYP2D6 dependent imipramine and desipramine metabolism; comparative studies with selected SSRIs, and effects on human hepatic CYP3A4, CYP2C9 and CYP1A2.
abstract: OBJECTIVE
  In order to anticipate drug-interactions of potential clinical significance the ability of the novel antidepressant, venlafaxine, to inhibit CYP2D6 dependent imipramine and desipramine 2-hydroxylation was investigated in human liver microsomes. The data obtained were compared with the selective serotonin re-uptake inhibitors, fluoxetine, sertraline, fluvoxamine and paroxetine. Venlafaxine's potential to inhibit several other major P450 s was also studied (CYP3A4, CYP2D6, CYP1A2).
  
  
  METHODS
  Ki values for venlafaxine, paroxetine, fluoxetine, fluvoxamine and sertraline as inhibitors of imipramine and desipramine 2-hydroxylation were determined from Dixon plots of control and inhibited rate data in human hepatic microsomal incubations. The inhibitory effect of imipramine and desipramine on liver microsomal CYP2D6 dependent venlafaxine O-demethylation was determined similarly. Venlafaxine's IC50 values for CYP3A4, CYP1A2 CYP2C9 were determined based on inhibition of probe substrate activities (testosterone 6 beta-hydroxylation, ethoxyresorufin O-dealkylase and tolbutamide 4-hydroxylation, respectively).
  
  
  RESULTS
  Fluoxetine, paroxetine, and fluvoxamine were potent inhibitors of imipramine 2-hydroxylase activity (Ki values of 1.6 +/- 0.8, 3.2 +/- 0.8 and 8.0 +/- 4.3 microM, respectively; mean +/- s.d., n = 3), while sertraline was less inhibitory (Ki of 24.7 +/- 8.9 microM). Fluoxetine also markedly inhibited desipramine 2-hydroxylation with a Ki of 1.3 +/- 0.5 microM. Venlafaxine was less potent an inhibitor of imipramine 2-hydroxylation (Ki of 41.0 +/- 9.5 microM) than the SSRIs that were studied. Imipramine and desipramine gave marked inhibition of CYP2D6 dependent venlafaxine O-demethylase activity (Ki values of 3.9 +/- 1.7 and 1.7 +/- 0.9 microM, respectively). Venlafaxine did not inhibit ethoxyresorufin O-dealkylase (CYP1A2), tolbutamide 4-hydroxylase (CYP2C9) or testosterone 6 beta-hydroxylase (CYP3A4) activities at concentrations of up to 1 mM.
  
  
  CONCLUSIONS
  It is concluded that venlafaxine has a low potential to inhibit the metabolism of substrates for CYP2D6 such as imipramine and desipramine compared with several of the most widely used SSRIs, as well as the metabolism of substrates for several of the other major human hepatic P450s.
authors.affiliation: Drug Safety and Metabolism, Wyeth-Ayerst Research, Princeton, NJ 08543-8000, USA.
authors.forename: S E
authors.initials: SE
authors.lastname: Ball
authors.forename: D
authors.initials: D
authors.lastname: Ahern
authors.forename: J
authors.initials: J
authors.lastname: Scatina
authors.forename: J
authors.initials: J
authors.lastname: Kao
mesh_terms: D015057:1-Naphthylamine / Q000031:analogs & derivatives / Q000493:pharmacokinetics / Q000494:pharmacology; D018687:Antidepressive Agents, Second-Generation / Q000493:pharmacokinetics / Q000494:pharmacology*; D000929:Antidepressive Agents, Tricyclic / Q000378:metabolism* / Q000493:pharmacokinetics; D001189:Aryl Hydrocarbon Hydroxylases; D002851:Chromatography, High Pressure Liquid; D003511:Cyclohexanols / Q000493:pharmacokinetics / Q000494:pharmacology*; D019388:Cytochrome P-450 CYP1A2 / Q000378:metabolism; D065609:Cytochrome P-450 CYP1A2 Inhibitors; D065729:Cytochrome P-450 CYP2C9; D019389:Cytochrome P-450 CYP2D6 / Q000378:metabolism; D065690:Cytochrome P-450 CYP2D6 Inhibitors; D051544:Cytochrome P-450 CYP3A; D065607:Cytochrome P-450 Enzyme Inhibitors; D003577:Cytochrome P-450 Enzyme System / Q000378:metabolism; D003891:Desipramine / Q000378:metabolism* / Q000493:pharmacokinetics; D005473:Fluoxetine / Q000493:pharmacokinetics / Q000494:pharmacology; D016666:Fluvoxamine / Q000493:pharmacokinetics / Q000494:pharmacology; D005629:Frozen Sections; D006801:Humans; D006900:Hydroxylation; D007099:Imipramine / Q000378:metabolism* / Q000493:pharmacokinetics; D066298:In Vitro Techniques; D007928:Lethal Dose 50; D008862:Microsomes, Liver / Q000187:drug effects / Q000201:enzymology*; D006899:Mixed Function Oxygenases / Q000037:antagonists & inhibitors / Q000378:metabolism; D017374:Paroxetine / Q000493:pharmacokinetics / Q000494:pharmacology; D017367:Selective Serotonin Reuptake Inhibitors / Q000493:pharmacokinetics / Q000494:pharmacology*; D020280:Sertraline; D039181:Steroid 16-alpha-Hydroxylase; D013250:Steroid Hydroxylases / Q000037:antagonists & inhibitors / Q000378:metabolism; D000069470:Venlafaxine Hydrochloride
chemical_list: D015057:1-Naphthylamine; D018687:Antidepressive Agents, Second-Generation; D000929:Antidepressive Agents, Tricyclic; D001189:Aryl Hydrocarbon Hydroxylases; D003511:Cyclohexanols; D019388:Cytochrome P-450 CYP1A2; D065609:Cytochrome P-450 CYP1A2 Inhibitors; D065729:Cytochrome P-450 CYP2C9; D019389:Cytochrome P-450 CYP2D6; D065690:Cytochrome P-450 CYP2D6 Inhibitors; D051544:Cytochrome P-450 CYP3A; D065607:Cytochrome P-450 Enzyme Inhibitors; D003577:Cytochrome P-450 Enzyme System; D003891:Desipramine; D005473:Fluoxetine; D016666:Fluvoxamine; D007099:Imipramine; D006899:Mixed Function Oxygenases; D017374:Paroxetine; D017367:Selective Serotonin Reuptake Inhibitors; D020280:Sertraline; D039181:Steroid 16-alpha-Hydroxylase; D013250:Steroid Hydroxylases; D000069470:Venlafaxine Hydrochloride; C450260:CYP2C9 protein, human; C504573:CYP1A2 protein, human; C104464:CYP3A protein, human; C510163:CYP3A4 protein, human