COMPLICATIONS WITH THE USE OF CARFENTANIL CITRATE AND XYLAZINE HYDROCHLORIDE TO IMMOBILIZE DOMESTIC HORSES

Carfentanil citrate, the only opioid approved in the United States for immobilizing large exotic animals, increasingly has been used to chem ically restrain exotic horses, such as Prezwalski's horses (Equus prze walskii) and wild horses (E caballus). Because carfentanil's duration of action is long and renarcotization may develop 2 to 24 hours after administration of antagonists, a study was designed to compare the phy siologic effects of opioid antagonists, using domestic horses chemical ly restrained with xylazine hydrochloride and carfentanil. The study w as terminated after the initial 3 horses developed severe tachycardia and hypertension, which resulted in the death of 1 horse from pulmonar y edema. Although it was possible that the clinical findings in these horses may have resulted from use of an inadequate dosage of carfentan il or xylazine, or both, analysis of the results more likely indicated that domestic and exotic horses may respond differently to carfentani l, and domestic horses may not be a good model for use in studies of c arfentanil.