title: Simultaneous assessment of drug interactions with low- and high-extraction opioids: application to parecoxib effects on the pharmacokinetics and pharmacodynamics of fentanyl and alfentanil.
abstract: BACKGROUND
  Parecoxib is a parenteral cyclooxygenase-2 (COX-2) inhibitor intended for perioperative analgesia. It is an inactive prodrug hydrolyzed in vivo to the active inhibitor valdecoxib, a substrate for hepatic cytochrome P450 3A4 (CYP3A4); hence, a potential exists for metabolic interactions with other CYP3A substrates. This study determined the effects of parecoxib on the pharmacokinetics and pharmacodynamics of the CYP3A substrates fentanyl and alfentanil compared with the CYP3A inhibitor troleandomycin. Alfentanil is a low-extraction drug with a clearance that is highly susceptible to drug interactions; fentanyl is a high-extraction drug and, thus, is theoretically less vulnerable. We therefore also tested the hypothesis that the extraction ratio influences the consequence of altered hepatic metabolism of these opioids.
  
  
  METHODS
  After Institutional Review Board-approved, written, informed consent was obtained, 12 22- to 40-yr-old healthy volunteers were enrolled in the study. The protocol was a randomized, double-blinded, balanced, placebo-controlled, three-session (placebo, parecoxib, or troleandomycin pretreatment) crossover. Subjects received both alfentanil (15 microg/kg) and fentanyl (5 microg/kg; 15-min intravenous infusion) 1 h after placebo, parecoxib (40 mg intravenously every 12 h), or troleandomycin (every 6 h). Study sessions were separated by 7 or more days. Opioid concentrations in venous blood were determined by liquid chromatography-mass spectrometry. Pharmacokinetic parameters were determined by noncompartmental analysis. Opioid effects were determined by pupillometry, respiratory rate, and Visual Analog Scale scores.
  
  
  RESULTS
  There were no significant differences between the placebo and parecoxib treatments in alfentanil or fentanyl plasma concentration, maximum observed plasma concentration, area under the plasma time-concentration time curve, clearance, elimination half-life, or volume of distribution. However, disposition of alfentanil, and to a lesser extent fentanyl, was significantly altered by troleandomycin. Clearances were reduced to 12% (0.64 +/- 0.25 ml. kg-1. min-1) and 61% (9.35 +/- 3.07) of control (5.53 +/- 2.16 and 15.3 +/- 5.0) for alfentanil and fentanyl (P < 0.001). Pupil diameter versus time curves were similar between placebo and parecoxib treatments but were significantly different after troleandomycin.
  
  
  CONCLUSIONS
  Single-dose parecoxib does not alter fentanyl or alfentanil disposition or clinical effects and does not appear to cause significant CYP3A drug interactions. CYP3A inhibition decreases alfentanil clearance more than fentanyl clearance, confirming that the extraction ratio influences the consequence of altered hepatic drug metabolism. Modified cassette, or "cocktail," dosing is useful for assessing drug interactions in humans.
authors.affiliation: Department of Anesthesiology, University of Washington, Seattle, Washington 98195, USA.
authors.forename: Andra E
authors.initials: AE
authors.lastname: Ibrahim
authors.forename: Jennifer
authors.initials: J
authors.lastname: Feldman
authors.forename: Aziz
authors.initials: A
authors.lastname: Karim
authors.forename: Evan D
authors.initials: ED
authors.lastname: Kharasch
mesh_terms: D000328:Adult; D000339:Affect / Q000187:drug effects; D015760:Alfentanil / Q000009:adverse effects* / Q000493:pharmacokinetics; D000465:Algorithms; D000701:Analgesics, Opioid / Q000009:adverse effects* / Q000493:pharmacokinetics; D000900:Anti-Bacterial Agents / Q000494:pharmacology; D001189:Aryl Hydrocarbon Hydroxylases / Q000378:metabolism; D001711:Biotransformation; D018592:Cross-Over Studies; D016861:Cyclooxygenase Inhibitors / Q000493:pharmacokinetics / Q000494:pharmacology*; D051544:Cytochrome P-450 CYP3A; D004311:Double-Blind Method; D004347:Drug Interactions; D005260:Female; D005283:Fentanyl / Q000009:adverse effects* / Q000493:pharmacokinetics; D006207:Half-Life; D006439:Hemodynamics / Q000187:drug effects; D006801:Humans; D007555:Isoxazoles / Q000493:pharmacokinetics / Q000494:pharmacology*; D008099:Liver / Q000201:enzymology; D008297:Male; D013058:Mass Spectrometry; D010089:Oxidoreductases, N-Demethylating / Q000378:metabolism; D011680:Pupil / Q000187:drug effects; D015656:Respiratory Mechanics / Q000187:drug effects; D014217:Troleandomycin / Q000494:pharmacology
chemical_list: D000701:Analgesics, Opioid; D000900:Anti-Bacterial Agents; D016861:Cyclooxygenase Inhibitors; D007555:Isoxazoles; D015760:Alfentanil; C409945:parecoxib; D014217:Troleandomycin; D001189:Aryl Hydrocarbon Hydroxylases; D051544:Cytochrome P-450 CYP3A; D010089:Oxidoreductases, N-Demethylating; D005283:Fentanyl