Xylazine (Xylazine HCl) is an alpha-2-adrenergic agonist (α2- adrenergic agonist). In veterinary medicine, xylazine is often used in combination with ketamine.

Xylazine provides muscle relaxation based on inhibition of the intraneural transmission of impulses in the central nervous system.² The degree of CNS inhibition facilitates xylazine providing dose-dependent, deep muscle relaxation and respiratory depression without inhibition of the nervous system’s more critical functions.

In 1981, researchers reported a comparative pharmacokinetics of xylazine in several species. The drug was administered intravenously and intramuscularly at recommended doses. Data was generated by analyzing serum drug concentration in samples obtained at 1, 2, 4, 8, 16, 30 and 120 minutes after xylazine administration. Compartmental analysis of the data was performed and the data best fitted a two-compartment open model.^3,4   

Table 1. Major pharmacokinetic parameters of xylazine in horse, cattle, sheep and dog after intravenous administration at 0.6, 0.2, 1.0 and 1.4 mg/kg, respectively:⁴

The terminal half-life of xylazine in all species was short, indicating that xylazine concentration decreases to undetectable levels within a few hours. The total body clearance varied significantly and was fastest in sheep and dogs, and slowest in horses. Xylazine clearance has been attributed mainly to metabolic factors. The volume of distribution was large in all species apparently because of the lipophilic nature of the compound.⁴

Pharmacokinetic parameters for xylazine after IM administration are shown in Table 2. There were no differences in the half-lives after IM administration when compared to those after IV administration. The T_max values were reached within 15 minutes from drug administration and the peak concentrations were very low. Because of the low concentrations of the drug in bovine plasma, pharmacokinetic parameters after IM administration could not be determined in cattle.⁴

Table 2. Major pharmacokinetic parameters of xylazine in horse, cattle, sheep and dog after intramuscular administration at 0.6, 0.2, 1.0 and 1.4 mg/kg, respectively:⁴

Emergent Abuse Warning

The illicit use of xylazine among injecting drug users (IDUs) on the island of Puerto Rico has drawn significant attention. Clinical findings reported that xylazine users presented limb skin lesions, ulcerations and greater physiological deterioration than heroin users only. Because xylazine use in the human population has been reported in other locations outside of Puerto Rico, it is believed that this substance could also emerge as an adulterant in other markets.⁵

Adverse Effects

The adverse effects of xylazine can include muscle tremors, seizures or slowed heart rate with partial heart block and slowed breathing rate. Increased urination sometimes occurs in cats. Dogs can swallow excess air and can bloat under the effects of xylazine, with stomach tubing being necessary to remove excess air in the stomach. Vomiting can occur following xylazine administration in dogs and cats.³

Where to Buy Xylazine

Xylaxine is available in the U.S. through pharmaceutical manufacturers and through veterinary custom compounding companies.  Please consult your veterinarian prior to beginning any treatment regimen.

FOR RX ONLY: A valid prescription from a licensed veterinarian is required for dispensing this medication.

²Khursheed R., et. al. Evaluation of xylazine and ketamine for total intravenous anesthesia in horses, American Journal of Veterinary Research 2005 66:6, 1002-1007.

³drugs.com.

⁴Garcia-Villar, R., Toutain, P-L., Alvinerie, M. and Ruckebusch, Y., (1981). The pharmacokinetics of xylazine hydrochloride: An interspecific study. J. Vet. Pharmacol. Therap. 4, 87-92.

⁵Torruella, R.A. Xylazine (veterinary sedative) use in Puerto Rico. Subst Abuse Treat Prev Policy 6, 7 (2011). https://doi.org/10.1186/1747-597X-6-7.