Pharmacokinetics and clinical effects of a subanesthetic continuous rate infusion of ketamine in awake horses.
OBJECTIVE
To determine the pharmacokinetics and clinical effects of a subanesthetic, continuous rate infusion of ketamine administered to healthy awake horses.


METHODS
8 adult horses.


METHODS
Ketamine hydrochloride was administered to 2 horses, in a pilot study, at rates ranging from 0.4 to 1.6 mg/kg/h for 6 hours to determine an appropriate dose that did not cause adverse effects. Ketamine was then administered to 6 horses for a total of 12 hours (3 horses at 0.4 mg/kg/h for 6 hours followed by 0.8 mg/kg/h for 6 hours and 3 horses at 0.8 mg/kg/h for 6 hours followed by 0.4 mg/kg/h for 6 hours). Concentration of ketamine in plasma, heart rate, respiratory rate, blood pressure, physical activity, and analgesia were measured prior to, during, and following infusion. Analgesic testing was performed with a modified hoof tester applied at a measured force to the withers and radius.


RESULTS
No signs of excitement and no significant changes in the measured physiologic variables during infusion rates of 0.4 and 0.8 mg of ketamine/kg/h were found. At 6 hours following infusions, heart rate and mean arterial pressure were decreased, compared with preinfusion measurements. An analgesic effect could not be demonstrated during or after infusion. Pharmacokinetic variables for 0.4 and 0.8 mg/kg/h infusions were not significantly different.


CONCLUSIONS
Ketamine can be administered to awake horses at 0.4 or 0.8 mg/kg/h without adverse behavioral effects. The observed pharmacokinetic values are different than those reported for single-dose IV bolus administration of this drug.
Fielding
C Langdon
CL
Department of Large Animal Medicine and Surgery, College of Veterinary Medicine and Biomedical Sciences, Texas A and M University, College Station, TX 77843-4474, USA.
Brumbaugh
Gordon W
GW
Matthews
Nora S
NS
Peck
Kenneth E
KE
Roussel
Allen J
AJ
D000698:Analgesia / Q000379:methods / Q000662:veterinary*; D000700:Analgesics / Q000008:administration & dosage / Q000097:blood / Q000493:pharmacokinetics*; D000818:Animals; D001794:Blood Pressure / Q000187:drug effects; D005260:Female; D006339:Heart Rate / Q000187:drug effects; D006736:Horses / Q000502:physiology*; D007262:Infusions, Intravenous / Q000662:veterinary; D007649:Ketamine / Q000008:administration & dosage / Q000097:blood / Q000493:pharmacokinetics*; D008297:Male; D010147:Pain Measurement / Q000662:veterinary; D010865:Pilot Projects; D012119:Respiration / Q000187:drug effects
D000700:Analgesics; D007649:Ketamine