title: An in vitro approach to potential methadone metabolic-inhibition interactions.
abstract: OBJECTIVE
  The aim of this study was to assess the drug interaction potential of psychotropic medication on methadone N-demethylation using cDNA-expressed cytochrome P450 CYP enzymes.
  
  
  METHODS
  Methadone was incubated with various drugs (n = 10) and cDNA-expressed CYP3A4, CYP2D6, CYP2B6, CYP2C19 and CYP1A2 enzymes to screen for their inhibition potency. The nature of enzyme selective activity for inhibition was further investigated for potent inhibitors. To test for a mechanism-based component in inhibition, all substances were tested with preincubation and without. 2-Ethylidene-1,5-dimethyl-3,3-diphenylpyrrolidine (EDDP) concentration was determined by liquid chromatography/tandem mass spectrometry following liquid/liquid extraction.
  
  
  RESULTS
  Formation of EDDP was catalysed by CYP3A4, CYP2D6 and CYP2C19. The N-demethylation of methadone was preferentially inhibited by amitriptyline, buprenorphine, methylenedioxymethamphetamine (MDMA) and zolpidem. Both amitriptyline and buprenorphine were strong, reversible inhibitors of CYP3A4. Similarly, amitriptyline and MDMA were identified as inhibitors of CYP2D6. Zolpidem revealed a mechanism-based inhibition of CYP3A4.
  
  
  CONCLUSIONS
  Amitriptyline, MDMA and zolpidem are likely to slow down conversion of methadone and to increase its area under the curve (AUC). A consideration of the in vitro evidence of drug-methadone interactions should help to improve patient care during methadone maintenance treatment.
authors.affiliation: Institute of Legal Medicine and Traffic Medicine, Ruprecht-Karls University, Vossstr. 2, 69115, Heidelberg, Germany.
authors.forename: Stephanie
authors.initials: S
authors.lastname: Bomsien
authors.forename: Gisela
authors.initials: G
authors.lastname: Skopp
mesh_terms: D000465:Algorithms; D000639:Amitriptyline / Q000378:metabolism / Q000494:pharmacology; D000701:Analgesics, Opioid / Q000378:metabolism / Q000494:pharmacology; D000069445:Atomoxetine Hydrochloride; D002853:Chromatography, Liquid / Q000379:methods; D015283:Citalopram / Q000378:metabolism / Q000494:pharmacology; D003024:Clozapine / Q000378:metabolism / Q000494:pharmacology; D065607:Cytochrome P-450 Enzyme Inhibitors; D003577:Cytochrome P-450 Enzyme System / Q000235:genetics / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D004347:Drug Interactions; D007527:Isoenzymes / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism; D007700:Kinetics; D008691:Methadone / Q000378:metabolism* / Q000494:pharmacology; D008745:Methylation; D018817:N-Methyl-3,4-methylenedioxyamphetamine / Q000378:metabolism / Q000494:pharmacology; D010089:Oxidoreductases, N-Demethylating / Q000037:antagonists & inhibitors / Q000378:metabolism / Q000494:pharmacology; D011437:Propylamines / Q000378:metabolism / Q000494:pharmacology; D011619:Psychotropic Drugs / Q000378:metabolism / Q000494:pharmacology; D011725:Pyridines / Q000378:metabolism / Q000494:pharmacology; D011759:Pyrrolidines / Q000037:antagonists & inhibitors / Q000378:metabolism; D053719:Tandem Mass Spectrometry / Q000379:methods; D000077334:Zolpidem
chemical_list: D000701:Analgesics, Opioid; D065607:Cytochrome P-450 Enzyme Inhibitors; D007527:Isoenzymes; D011437:Propylamines; D011619:Psychotropic Drugs; D011725:Pyridines; D011759:Pyrrolidines; D015283:Citalopram; D000639:Amitriptyline; D000069445:Atomoxetine Hydrochloride; D000077334:Zolpidem; D003577:Cytochrome P-450 Enzyme System; D010089:Oxidoreductases, N-Demethylating; D003024:Clozapine; D018817:N-Methyl-3,4-methylenedioxyamphetamine; D008691:Methadone; C010724:2-ethylidene-1,5-dimethyl-3,3-diphenylpyrrolidine