title: Individual differences in morphine and butorphanol analgesia: a laboratory pain study.
abstract: OBJECTIVE
  Responses to opioid analgesics are highly variable, and the understanding of contributing factors is limited. This laboratory study was designed to examine the contributions of sex and race to inter-individual variability in response to opioids.
  
  
  METHODS
  A randomized, double-blind, mixed design was implemented in the evaluation of analgesic response to a µ-opioid agonist and mixed agonist-antagonist, using three well-validated experimental pain assays (thermal, pressure, and ischemic).
  
  
  METHODS
  Participants included a total of 142 healthy subjects (76 men/66 women), 119 non-Hispanic whites and 23 African Americans.
  
  
  METHODS
  Three sessions of pain testing were completed prior to and following an intravenous administration of morphine (0.08 mg/kg), butorphanol (0.016 mg/kg), and placebo (saline) in counterbalanced order.
  
  
  METHODS
  A change score was calculated from the difference between the pre-drug and postdrug values. Three separate change scores (morphine, saline, and butorphanol) were computed for each experimental pain variable. Mixed-model analyses of covariance were performed on analgesic change scores.
  
  
  RESULTS
  Significant sex differences emerged for predrug pain measures with minimal differences for race. Sex differences in opioid analgesia were not demonstrated. However, significant race differences and race X drug interactions emerged for thermal, pressure, and ischemic pain measures. The pattern of results generally indicated that for pressure and ischemic pain, African American subjects showed greater analgesic responses to both medications compared with non-Hispanic whites. For thermal pain threshold, butorphanol but not morphine analgesia was greater for African American vs non-Hispanic whites.
  
  
  CONCLUSIONS
  Findings are among the first to demonstrate race differences in a laboratory study of opioid analgesia.
authors.affiliation: Community Dentistry and Behavioral Science, College of Dentistry, University of Florida, Gainesville, FL 32610-3629, USA. ksibille@ufl.edu
authors.forename: Kimberly T
authors.initials: KT
authors.lastname: Sibille
authors.forename: Lindsay L
authors.initials: LL
authors.lastname: Kindler
authors.forename: Toni L
authors.initials: TL
authors.lastname: Glover
authors.forename: Ricardo D
authors.initials: RD
authors.lastname: Gonzalez
authors.forename: Roland
authors.initials: R
authors.lastname: Staud
authors.forename: Joseph L
authors.initials: JL
authors.lastname: Riley
authors.forename: Roger B
authors.initials: RB
authors.lastname: Fillingim
mesh_terms: D000293:Adolescent; D000328:Adult; D000701:Analgesics, Opioid / Q000627:therapeutic use*; D002077:Butorphanol / Q000627:therapeutic use*; D004311:Double-Blind Method; D005006:Ethnicity; D005260:Female; D006801:Humans; D007206:Individuality; D008297:Male; D008875:Middle Aged; D009020:Morphine / Q000627:therapeutic use*; D010146:Pain / Q000188:drug therapy*; D010147:Pain Measurement; D010919:Placebos; D055815:Young Adult
chemical_list: D000701:Analgesics, Opioid; D010919:Placebos; D009020:Morphine; D002077:Butorphanol