Pharmacokinetics and pharmacodynamics of butorphanol in llamas after intravenous and intramuscular administration.
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.
Carroll
G L
GL
Department of Small Animal Medicine, College of Veterinary Medicine, Texas A&M University, College Station 77843-4474, USA.
Boothe
D M
DM
Hartsfield
S M
SM
Martinez
E A
EA
Spann
A C
AC
Hernandez
A
A
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
D000701:Analgesics, Opioid; D002077:Butorphanol