Can Ketamine be Given Intramuscularly to Horses to Aid in Standing Sedation?

Final Lay Report 

“Can ketamine be given intramuscularly to horses to aid in standing sedation?” 

b.  Investigators: 

1.) Sarah S. le Jeune, DVM

2.) Laurie K. Bohannon, DVM

3.) Jodie Daglish, BVSc 

3.) Alonso Guedes, DVM, MS, PhD

4.) Bruno Pypendop, DrMedVet, DrVetSci

c.  Brief Background of the Problem:

Anecdotally, ketamine, and injectable anesthetic agent, has been given intramuscularly (IM) to help with standard sedation in hyperexcitable and hypersensitive horses. Sedation is used commonly in horses, for example for routine joint injections and stem cell injections and for dental procedures. However, the efficacy of IM ketamine as an adjunctive sedative and the disposition of IM ketamine has not been reported in horses and this a necessary step to establish dosing regimens.

d.  Hypothesis Statement 

We predict that IM ketamine will aid in standing sedation in horses. In addition, this study will provide information regarding the disposition of IM ketamine in horses.

e.  Specific Objective(s) of the Study that addresses the problem:

The goal of this study is to describe the sedative effect of IM ketamine in horses in combination with the alpha-2 agonist detomidine, and to characterize the pharmacokinetics (disposition) of ketamine administered intramuscularly to horses. 

f.  Overview of Experimental Approach 

Six healthy adult research horses (male and females, of several breeds) were used in the study. Horses underwent 4 different experiments: no drug (saline), detomidine IV (0.01mg/kg) and ketamine IM (0.6mg/kg), ketamine IV alone (0.3mg/kg), ketamine IM alone at a one-week interval. The order of treatments was randomized. The study was double-blinded so that the investigator did not know which horse was receiving which treatment. 

The following responses were measured: 

Temperature, heart rate, respiratory rate, sedation score, number of steps per min (pedometer), and distance from chin to ground, prior to drug administration, and every 10 min for 1 hour, every 20 min for 3 hours, and hourly for 4 hours thereafter.

Venous blood samples were collected prior to drug administration, and 2, 4, 8, 15, 30, 60, 120, 240, and 480 minutes thereafter to determine plasma ketamine concentrations.

g.  Anticipated Benefits to the Equine Industry:

The results of the study will characterize the disposition of ketamine administered intramuscularly to horses and help provide a dosing regimen necessary for standing sedation in the difficult horse.  

h.  Results: 

Ketamine at a dose of 0.6mg/kg could be administered intramuscularly to horses and was well tolerated by all animals in the study. Ketamine administered alone (IV or IM) did not produce adequate levels of sedation. Administration of ketamine IM in addition to detomidine IV, produced a level of sedation in horses that was similar to detomidine IV alone, but horses were less sensitive to touching of the forelimb than with detomidine alone. This effect lasted 20 minutes. Ketamine IM could therefore be added to a routine sedation protocol for procedures on the limbs, such as routine joint injections, in refractory horses.

The disposition of ketamine was characterized and it was shown that intramuscularly administered ketamine was poorly absorbed. In addition, detomidine affected the disposition of ketamine.

Adding IM ketamine to routine sedation protocols is a valid option for difficult/hypersensitive horses.

i.  Summary: 

Pending further research, ketamine can be administered intramuscularly to aid in standing sedation in horses.  

j.  Acknowledgment: 

This project was supported by the Center for Equine Health with funds provided by the State of California satellite wagering fund and contributions by private donors.