Pharmacokinetics and adverse effects of butorphanol administered by single intravenous injection or continuous intravenous infusion in horses.
OBJECTIVE
To determine an infusion rate of butorphanol tartrate in horses that would maintain therapeutic plasma drug concentrations while minimizing development of adverse behavioral and gastrointestinal tract effects.


METHODS
10 healthy adult horses.


METHODS
Plasma butorphanol concentrations were determined by use of high-performance liquid chromatography following administration of butorphanol by single IV injection (0.1 to 0.13 mg/kg of body weight) or continuous IV infusion (loading dose, 17.8 microg/kg; infusion dosage, 23.7 microg/kg/h for 24 hours). Pharmacokinetic variables were calculated, and changes in physical examination data, gastrointestinal tract transit time, and behavior were determined over time.


RESULTS
A single IV injection of butorphanol was associated with adverse behavioral and gastrointestinal tract effects including ataxia, decreased borborygmi, and decreased defecation. Elimination half-life of butorphanol was brief (44.37 minutes). Adverse gastrointestinal tract effects were less apparent during continuous 24-hour infusion of butorphanol at a dosage that resulted in a mean plasma concentration of 29 ng/ml, compared with effects after a single IV injection. No adverse behavioral effects were observed during or after continuous infusion.


CONCLUSIONS
Continuous IV infusion of butorphanol for 24 hours maintained plasma butorphanol concentrations within a range associated with analgesia. Adverse behavioral and gastrointestinal tract effects were minimized during infusion, compared with a single injection of butorphanol. Continuous infusion of butorphanol may be a useful treatment to induce analgesia in horses.
Sellon
D C
DC
Department of Food Animal and Equine Medicine, College of Veterinary Medicine, North Carolina State University, Raleigh 27606, USA.
Monroe
V L
VL
Roberts
M C
MC
Papich
M G
MG
D000701:Analgesics, Opioid / Q000008:administration & dosage / Q000009:adverse effects* / Q000493:pharmacokinetics*; D000818:Animals; D001522:Behavior, Animal / Q000187:drug effects*; D002077:Butorphanol / Q000008:administration & dosage / Q000009:adverse effects* / Q000493:pharmacokinetics*; D002851:Chromatography, High Pressure Liquid; D018592:Cross-Over Studies; D005260:Female; D005772:Gastrointestinal Transit / Q000187:drug effects*; D006207:Half-Life; D006736:Horses / Q000378:metabolism*; D007262:Infusions, Intravenous / Q000662:veterinary; D007275:Injections, Intravenous / Q000662:veterinary; D008297:Male
D000701:Analgesics, Opioid; D002077:Butorphanol