title: Genetic polymorphisms and drug interactions modulating CYP2D6 and CYP3A activities have a major effect on oxycodone analgesic efficacy and safety.
abstract: OBJECTIVE
  The major drug-metabolizing enzymes for the oxidation of oxycodone are CYP2D6 and CYP3A. A high interindividual variability in the activity of these enzymes because of genetic polymorphisms and/or drug-drug interactions is well established. The possible role of an active metabolite in the pharmacodynamics of oxycodone has been questioned and the importance of CYP3A-mediated effects on the pharmacokinetics and pharmacodynamics of oxycodone has been poorly explored.
  
  
  METHODS
  We conducted a randomized crossover (five arms) double-blind placebo-controlled study in 10 healthy volunteers genotyped for CYP2D6. Oral oxycodone (0.2 mg x kg(-1)) was given alone or after inhibition of CYP2D6 (with quinidine) and/or of CYP3A (with ketoconazole). Experimental pain (cold pressor test, electrical stimulation, thermode), pupil size, psychomotor effects and toxicity were assessed.
  
  
  RESULTS
  CYP2D6 activity was correlated with oxycodone experimental pain assessment. CYP2D6 ultra-rapid metabolizers experienced increased pharmacodynamic effects, whereas cold pressor test and pupil size were unchanged in CYP2D6 poor metabolizers, relative to extensive metabolizers. CYP2D6 blockade reduced subjective pain threshold (SPT) for oxycodone by 30% and the response was similar to placebo. CYP3A4 blockade had a major effect on all pharmacodynamic assessments and SPT increased by 15%. Oxymorphone C(max) was correlated with SPT assessment (rho(S)= 0.7) and the only independent positive predictor of SPT. Side-effects were observed after CYP3A4 blockade and/or in CYP2D6 ultra-rapid metabolizers.
  
  
  CONCLUSIONS
  The modulation of CYP2D6 and CYP3A activities had clear effects on oxycodone pharmacodynamics and these effects were dependent on CYP2D6 genetic polymorphism.
authors.affiliation: Clinical Pharmacology and Toxicology and Multidisciplinary Pain Centre, Department of Anaesthesiology, Pharmacology and Intensive Care, Geneva University Hospitals, Geneva, Switzerland. Caroline.Samer@hcuge.ch
authors.forename: C F
authors.initials: CF
authors.lastname: Samer
authors.forename: Y
authors.initials: Y
authors.lastname: Daali
authors.forename: M
authors.initials: M
authors.lastname: Wagner
authors.forename: G
authors.initials: G
authors.lastname: Hopfgartner
authors.forename: C B
authors.initials: CB
authors.lastname: Eap
authors.forename: M C
authors.initials: MC
authors.lastname: Rebsamen
authors.forename: M F
authors.initials: MF
authors.lastname: Rossier
authors.forename: D
authors.initials: D
authors.lastname: Hochstrasser
authors.forename: P
authors.initials: P
authors.lastname: Dayer
authors.forename: J A
authors.initials: JA
authors.lastname: Desmeules
mesh_terms: D000328:Adult; D000701:Analgesics, Opioid / Q000009:adverse effects / Q000493:pharmacokinetics / Q000494:pharmacology / Q000627:therapeutic use*; D018592:Cross-Over Studies; D019389:Cytochrome P-450 CYP2D6 / Q000235:genetics* / Q000378:metabolism*; D065690:Cytochrome P-450 CYP2D6 Inhibitors; D051544:Cytochrome P-450 CYP3A / Q000378:metabolism*; D065692:Cytochrome P-450 CYP3A Inhibitors; D004311:Double-Blind Method; D004347:Drug Interactions; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005838:Genotype; D006801:Humans; D008297:Male; D050216:Metabolic Detoxication, Phase I / Q000235:genetics; D008875:Middle Aged; D010098:Oxycodone / Q000009:adverse effects* / Q000493:pharmacokinetics / Q000494:pharmacology / Q000627:therapeutic use*; D010111:Oxymorphone / Q000097:blood; D017288:Pain Threshold / Q000187:drug effects; D010641:Phenotype; D011110:Polymorphism, Genetic; D011597:Psychomotor Performance / Q000187:drug effects; D012025:Reflex, Pupillary / Q000187:drug effects; D055815:Young Adult
chemical_list: D000701:Analgesics, Opioid; D065690:Cytochrome P-450 CYP2D6 Inhibitors; D065692:Cytochrome P-450 CYP3A Inhibitors; D004791:Enzyme Inhibitors; D010111:Oxymorphone; D010098:Oxycodone; C104464:CYP3A protein, human; D019389:Cytochrome P-450 CYP2D6; D051544:Cytochrome P-450 CYP3A