title: Pharmacokinetics and pharmacodynamics of butorphanol in llamas after intravenous and intramuscular administration.
abstract: OBJECTIVE
  To evaluate disposition of butorphanol after i.v. and i.m. administration, effects on physiologic variables, and analgesic efficacy after i.m. administration in llamas.
  
  
  METHODS
  Nonrandomized crossover study.
  
  
  METHODS
  6 healthy adult male llamas.
  
  
  METHODS
  Butorphanol (0.1 mg/kg [0.045 mg/lb] of body weight) was administered i.m. first and i.v. 1 month later. Blood samples were collected intermittently for 24 hours after administration. Plasma butorphanol versus time curves were subjected to pharmacokinetic analysis. Two months later, butorphanol (0.1 mg/kg) was administered i.m., and physiologic variables and analgesia were assessed.
  
  
  RESULTS
  Extrapolated peak plasma concentrations after i.v. and i.m. administration were 94.8 +/- 53.1 and 34.3 +/- 11.6 ng/ml, respectively. Volume of distribution at steady state after i.v. administration was 0.822 +/- 0.329 L/kg per minute and systemic clearance was 0.050 +/- 0.014 L/kg per minute. Slope of the elimination phase was significantly different, and elimination half-life was significantly shorter after i.v. (15.9 +/- 9.1 minutes) versus i.m. (66.8 +/- 13.5 minutes) administration. Bioavailability was 110 +/- 49% after i.m. administration. Heart rate decreased and rectal temperature increased. Somatic analgesia was increased for various periods. Two llamas became transiently sedated, and 2 became transiently excited after butorphanol administration.
  
  
  CONCLUSIONS
  Although i.v. administration of butorphanol results in a short half-life that may limit its analgesic usefulness, the elimination half-life of butorphanol administered i.m. is likely to be clinically useful. The relationship among plasma butorphanol concentration, time, and analgesia differed with the somatic analgesia model; clinically useful analgesia may occur at lower plasma concentrations than those reported here.
authors.affiliation: Department of Small Animal Medicine, College of Veterinary Medicine, Texas A&M University, College Station 77843-4474, USA.
authors.forename: G L
authors.initials: GL
authors.lastname: Carroll
authors.forename: D M
authors.initials: DM
authors.lastname: Boothe
authors.forename: S M
authors.initials: SM
authors.lastname: Hartsfield
authors.forename: E A
authors.initials: EA
authors.lastname: Martinez
authors.forename: A C
authors.initials: AC
authors.lastname: Spann
authors.forename: A
authors.initials: A
authors.lastname: Hernandez
mesh_terms: D000701:Analgesics, Opioid / Q000008:administration & dosage / Q000493:pharmacokinetics* / Q000494:pharmacology*; D000818:Animals; D001682:Biological Availability; D001831:Body Temperature / Q000187:drug effects; D002077:Butorphanol / Q000008:administration & dosage / Q000493:pharmacokinetics* / Q000494:pharmacology*; D002161:Camelids, New World / Q000378:metabolism* / Q000502:physiology; D018592:Cross-Over Studies; D006207:Half-Life; D006339:Heart Rate / Q000187:drug effects; D007273:Injections, Intramuscular / Q000662:veterinary; D007275:Injections, Intravenous / Q000662:veterinary; D008297:Male; D008657:Metabolic Clearance Rate
chemical_list: D000701:Analgesics, Opioid; D002077:Butorphanol