title: Pharmacodynamic effects of oral oxymorphone: abuse liability, analgesic profile and direct physiologic effects in humans.
abstract: Oxymorphone is a semisynthetic μ-opioid agonist, marketed as a prescription analgesic purported to be twice as potent as oxycodone for pain relief. Oral formulations of oxymorphone were reintroduced in the United States in 2006 and reports of abuse ensued; however, there are limited data available on its pharmacodynamic effects. The current study aimed to examine the direct physiologic effects, relative abuse liability, analgesic profile and overall pharmacodynamic potency of oxymorphone in comparison with identical doses of oxycodone. Healthy, non-dependent opioid abusers (n = 9) were enrolled in this within-subject, double-blind, placebo-controlled, 3-week inpatient study. Seven experimental sessions (6.5 hours) were conducted, during which an oral dose of immediate-release formulations of oxymorphone (10, 20 and 40 mg), oxycodone (10, 20 and 40 mg) or placebo was administered. An array of physiologic, abuse liability and experimental pain measures was collected. At identical doses, oxymorphone produced approximately twofold less potent effects on miosis, compared with oxycodone. Oxymorphone also produced lesser magnitude effects on measures of respiratory depression, two experimental pain models and observer-rated agonist effects. However, 40 mg of oxymorphone was similar to 40 mg of oxycodone on several abuse-related subjective ratings. Formal relative potency analyses were largely invalid because of the substantially greater effects of oxycodone. Overall, oxymorphone is less potent on most pharmacodynamic measures, although at higher doses, its abuse liability is similar to oxycodone. These data suggest that the published clinical equianalgesic estimates may not be consistent with the observed direct physiologic effects of opioids, results of experimental pain models or abuse liability measures, as assessed in the human laboratory.
authors.affiliation: College of Medicine, Department of Behavioral Science, University of Kentucky, Lexington, USA.|Center on Drug and Alcohol Research, University of Kentucky, Lexington, USA.
authors.forename: Shanna
authors.initials: S
authors.lastname: Babalonis
authors.affiliation: College of Medicine, Department of Behavioral Science, University of Kentucky, Lexington, USA.|Center on Drug and Alcohol Research, University of Kentucky, Lexington, USA.|College of Medicine, Department of Psychiatry, University of Kentucky, Lexington, KY, USA.
authors.forename: Michelle R
authors.initials: MR
authors.lastname: Lofwall
authors.affiliation: Center on Drug and Alcohol Research, University of Kentucky, Lexington, USA.
authors.forename: Paul A
authors.initials: PA
authors.lastname: Nuzzo
authors.affiliation: College of Medicine, Department of Behavioral Science, University of Kentucky, Lexington, USA.|Center on Drug and Alcohol Research, University of Kentucky, Lexington, USA.|College of Medicine, Department of Psychiatry, University of Kentucky, Lexington, KY, USA.|College of Pharmacy, Department of Pharmaceutical Sciences, University of Kentucky, Lexington, KY, USA.|College of Medicine, Department of Pharmacology, University of Kentucky, Lexington, KY, USA.
authors.forename: Sharon L
authors.initials: SL
authors.lastname: Walsh
mesh_terms: D000284:Administration, Oral; D000328:Adult; D000701:Analgesics, Opioid / Q000008:administration & dosage / Q000494:pharmacology*; D001794:Blood Pressure / Q000187:drug effects; D003071:Cognition / Q000187:drug effects*; D003080:Cold Temperature; D018592:Cross-Over Studies; D004311:Double-Blind Method; D005260:Female; D006339:Heart Rate / Q000187:drug effects; D006801:Humans; D008297:Male; D009293:Opioid-Related Disorders; D010111:Oxymorphone / Q000008:administration & dosage / Q000494:pharmacology*; D010146:Pain / Q000517:prevention & control*; D010147:Pain Measurement / Q000187:drug effects*; D011312:Pressure
chemical_list: D000701:Analgesics, Opioid; D010111:Oxymorphone
keywords: Abuse liability; cold pressor; experimental pain models; oxycodone; oxymorphone; pressure algometer