Xylazine

Xylazine is a drug used for sedation, anesthesia, muscle relaxation, and analgesia in animals such as horses, cattle, and other non-human mammals.[1] It is an analog of clonidine and an agonist at the α2 class of adrenergic receptor.[2]

In veterinary anesthesia, xylazine is often used in combination with ketamine. Veterinarians also use xylazine as an emetic, especially in cats.[3] It is sold under many brand names worldwide, most notably the Bayer brand name Rompun.[1] It is also marketed as Anased, Sedazine, and Chanazine.[4] The drug interactions vary with different animals.[5][6][7]

Xylazine has become a drug of abuse in the United States, where it is known by the street name “tranq”, particularly in Puerto Rico.[8] The drug is being diverted from stocks used by equine veterinarians and used as a cutting agent for heroin and fentanyl, causing skin sores and infections at injection sites, as well as other health issues.[9] Fentanyl

ide effects in animals include transient hypertension, hypotension, and respiratory depression.[4] Further, the decrease of tissue sensitivity to insulin leads to xylazine-induced hyperglycemia and a reduction of tissue glucose uptake and utilization.[14] The duration of effects in animals lasts up to 4 hours.[4]

Pharmacokinetics
In dogs, sheep, horses, and cattle, the half-life is very short: only 1.21–5.97 minutes. Complete elimination of the drug can take up to 23.11 minutes in sheep and up to 49.51 minutes in horses.[2][4] In young rats, the half life is one hour.[16] Xylazine has a large volume of distribution (Vd).[4] The Vd = 1.9–2.5 for horses, cattle, sheep, and dogs.[4] Though the peak plasma concentrations are reached in 12–14 minutes in all species, the bioavailability varies between species.[4] The half life depends on the age of the animal, as age is related to prolonged duration of anesthesia and recovery time.[16] Toxicity occurs with repeated administration, given that the metabolic clearance of the drug is usually calculated as 7–9 times the half-life, which is 4 to 5 days for the clearance of xylazine.