How is xylazine (injection) used in veterinary sedation?

Xylazine Use in Veterinary Sedation

Xylazine injection is primarily used in veterinary medicine as a sedative, analgesic, and muscle relaxant for horses and Cervidae (deer species and elk) at specific dosages based on animal type and weight, with intramuscular administration being the most common route. 1

Dosage and Administration

Horses

• Intramuscular (IM): 1.0 mL/100 lbs body weight (1.0 mg/lb)
• Intravenous (IV): 0.5 mL/100 lbs body weight (0.5 mg/lb) 1

Cervidae (Deer and Elk)

• Intramuscular only (hand syringe or dart):
  • Fallow Deer: 2.0-4.0 mL/100 lbs (2.0-4.0 mg/lb)
  • Mule Deer: 1.0-2.0 mL/100 lbs (1.0-2.0 mg/lb)
  • Sika Deer: 1.0-2.0 mL/100 lbs (1.0-2.0 mg/lb)
  • White-Tailed Deer: 1.0-2.0 mL/100 lbs (1.0-2.0 mg/lb)
  • Elk: 0.25-0.5 mL/100 lbs (0.25-0.5 mg/lb) 1

Clinical Effects and Duration

Following injection, the animal should rest quietly until the full effect develops:

• Sedation: Usually maintained for 1-2 hours
• Analgesia: Lasts for 15-30 minutes 1

Veterinary Clinical Applications

Horses

1. Diagnostic procedures:

   • Oral and ophthalmic examinations
   • Abdominal and rectal palpation
   • Vaginal examination
   • Bladder catheterization
   • Radiographic examinations

2. Orthopedic procedures:

   • Application of casting materials and splints

3. Dental procedures

4. Minor surgical procedures:

   • Debridement
   • Removal of cutaneous neoplasms
   • Suturing lacerations

5. Behavioral management:

   • Calming and facilitating handling of fractious animals

6. Therapeutic use:

   • Sedation and pain relief following injury or surgery

7. Major surgical procedures:

   • As a preanesthetic to general anesthesia
   • In conjunction with local anesthetics 1

Cervidae (Deer and Elk)

1. Behavioral management:

   • Calming and facilitating handling of fractious animals

2. Diagnostic procedures

3. Minor surgical procedures

4. Therapeutic use:

   • Sedation and pain relief following injury or surgery

5. As a preanesthetic to local anesthesia 1

Pharmacological Properties and Mechanism

Xylazine stimulates presynaptic α-2 adrenergic receptors in the brain, triggering a negative feedback signal that reduces central catecholamine release. This results in:

• Decreased sympathetic nervous system outflow
• Sedation
• Relative and generally limited hypotension and bradycardia 2

In large doses, xylazine initially causes peripheral vasoconstriction and occasionally transient hypertension due to its effects on vascular α-adrenergic receptors 2. In mice and rats, xylazine is often combined with ketamine for anesthesia, with specific dosages:

• Mice: Ketamine (100 mg/kg), xylazine (20 mg/kg), and atropine (0.6 mg/kg)
• Rats: Ketamine (50-75 mg/kg) and xylazine (1-5 mg/kg) 2

Important Considerations and Precautions

1. Anesthetic combinations:

   • Xylazine can be used as a preanesthetic agent with barbiturates (pentobarbital, thiopental)
   • When used with barbiturates, only 1/3 to 1/2 of the calculated barbiturate dosage is needed 1
   • Can be combined with local anesthetics like procaine or lidocaine 1

2. Potential adverse effects:

   • Bradycardia (can be prevented with atropine at 0.02-0.05 mg/kg) 2
   • Hypotension
   • Respiratory depression (though no direct effect on respiratory drive) 2

3. Human misuse concerns:

   • Not approved for human use
   • Has emerged as an adulterant in recreational drugs, particularly opioids 3, 4
   • Human intoxication can cause central nervous system depression, respiratory depression, bradycardia, hypotension, and even death 4
   • No specific antidote for humans; naloxone is ineffective for xylazine toxicity 5

Monitoring and Recovery

• Animals should be allowed to rest quietly until the full effect has been reached
• Post-anesthetic or emergence excitement has not been observed in animals preanesthetized with xylazine 1
• Monitor for bradycardia and hypotension, especially when combined with other anesthetics

By understanding the proper dosing, administration, and clinical applications of xylazine in veterinary medicine, practitioners can effectively utilize this sedative while minimizing potential risks.