Xylazine is used in horses to produce sedation accompanied by a shorter period of analgesia. This article is about the use, contraindications, toxic effects, dosages, and association drug rules that apply to this medication. Also covered is the use of reveral agents yohimbine and tolazoline.

• Diagnostic procedures - oral and ophthalmic examinations, abdominal palpation, rectal palpation, vaginal examination, catheterization of the bladder and radiographic examinations.
• Orthopedic procedures, such as application of casting materials and splints.
• Dental procedures.
• Minor surgical procedures of short duration such as debridement, removal of cutaneous neoplasms and suturing of lacerations.
• To calm and facilitate handling of fractious animals.
• Therapeutic medication for sedation and relief of pain following injury or surgery.
• Major surgical procedures:
  • When used as a preanesthetic to general anesthesia.
  • Used in conjunction with local anesthetics.
  • One of the biggest problems in equine general anesthesia has been the injury rate of the recovering horse while standing. The horse tends to want to rise while still remarkably incoordinated from the general anesthetic. There is a growing body of evidence that post induction (where the horse is knocked out) treatment with xylazine (Rompun) results in a smoother recovery with fewer attempts to rise and more coordination on the first attempt.

XYLAZINE HCL INJECTION 100 MG Rx ProLabs Analgesic-Sedative (Xylazine) ANADA No.: 200-139 Active Ingredient(s): Each mL contains 100 mg xylazine, (base equivalent), 0.9 mg methylparaben, 0.1 mg propylparaben, water for injection; citric acid and sodium citrate for pH adjustment to 5.5 � 0.3. Xylazine hydrochloride (equivalent to 10% base) 11.4% Inert ingredients 88.6%   100.0% Indications: XYLAZINE HCL INJECTION (xylazine) should be used in horses when it is desirable to produce a state of sedation accompanied by a shorter period of analgesia. Horses: XYLAZINE HCL INJECTION (xylazine) has been used successfully as follows: 1. Diagnostic procedures - oral and ophthalmic examinations, abdominal palpation, rectal palpation, vaginal examination, catheterization of the bladder and radiographic examinations. 2. Orthopedic procedures, such as application of casting materials and splints. 3. Dental procedures. 4. Minor surgical procedures of short duration such as debridement, removal of cutaneous neoplasms and suturing of lacerations. 5. To calm and facilitate handling of fractious animals. 6. Therapeutic medication for sedation and relief of pain following injury or surgery. 7. Major surgical procedures: When used as a preanesthetic to general anesthesia. When used in conjunction with local anesthetics. Pharmacology: XYLAZINE HCL INJECTION (xylazine), a non-narcotic compound, is a sedative and analgesic as well as muscle relaxant. Its sedative and analgesic activity is related to central nervous system depression. Its muscle relaxant effect is based on inhibition of the intraneural transmission of impulses in the central nervous system. The principal pharmacological activities develop within 10 to 15 minutes after intramuscular injection in horses, and within 3 to 5 minutes following intravenous administration in horses. A sleeplike state, the depth of which is dose-dependent, is usually maintained for 1 to 2 hours, while analgesia lasts from 15 to 30 minutes. The centrally-acting muscle relaxant effect causes relaxation of the skeletal musculature, complementing sedation and analgesia. In horses under the influence of XYLAZINE HCL INJECTION (xylazine), the respiratory rate is reduced as in natural sleep. Following treatment with XYLAZINE HCL INJECTION (xylazine), the heart rate is decreased and a transient change in the conductivity of the cardiac muscle may occur, as evidenced by a partial atrioventricular block. This resembles the atrioventricular block often observed in normal horses.1,2,3,4 Partial A-V block may occasionally occur following intramuscular injection of XYLAZINE HCL INJECTION (xylazine). When given intravenously in horses, the incidence of partial A-V block is higher. Intravenous administration causes a transient rise in blood pressure in horses, followed by a slight decrease. XYLAZINE HCL INJECTION (xylazine) has no effect on blood clotting time or other hematologic parameters. Dosage and Administration: 1. Dosage: Intravenously - 0.5 mL/100 lbs body weight (0.5 mg/lb). Intramuscularly - 1.0 mL/100 lbs body weight (1.0 mg/lb). Following injection of XYLAZINE HCL INJECTION (xylazine) the animal should be allowed to rest quietly until the full effect has been reached. These dosages produce sedation which is usually maintained for 1 to 2 hours, and analgesia which lasts for 15 to 30 minutes. 2. Preanesthetic to Local Anesthesia: XYLAZINE HCL INJECTION (xylazine) at the recommended dosages can be used in conjunction with local anesthetics, such as procaine or lidocaine. 3. Preanesthetic to General Anesthesia: XYLAZINE HCL INJECTION (xylazine) at the recommended dosage rates produces an additive effect to central nervous system depressants such as pentobarbital sodium, thiopental sodium and thiamyl sodium. Therefore, the dosage of such compounds should be reduced and administered to the desired effect. In general, only 1/3 to � of the calculated dosage of the barbiturates will be needed to produce a surgical plane of anesthesia. Post-anesthetic or emergence excitement has not been observed in animals preanesthetized with XYLAZINE HCL INJECTION (xylazine). XYLAZINE HCL INJECTION (xylazine) has been used successfully as a preanesthetic agent for pentobarbital sodium, thiopental sodium, thiamylal sodium, nitrous oxide, ether, halothane, glyceryl guaiacolate and methoxyflurane anesthesia. Withdrawal Time: This drug should not be administered to domestic food-producing animals. Not for use in horses intended for food. Precaution(s): Store at controlled room temperature (15 to 30C or 59 to 86F). Caution(s): Federal law restricts this drug to use by or on the order of a licensed veterinarian. Careful consideration should be given before administering to horses with significantly depressed respiration, severe pathologic heart disease, advanced liver or kidney disease, severe endotoxic or traumatic shock and stress conditions such as extreme heat, cold, high altitude or fatigue. Do not use XYLAZINE HCL INJECTION (xylazine) in conjunction with tranquilizers. Analgesic effect is variable, and depth should be carefully assayed prior to surgical/clinical procedures. Variability of analgesia occurs most frequently at the distal extremities of horses. In spite of sedation, the practitioner and handlers should proceed with caution since defense reactions may not be diminished. Horses: Since an additive effect results from the use of XYLAZINE HCL INJECTION (xylazine) and the barbiturate compounds, it should be used with caution with these central nervous system depressants. Products known to produce respiratory depression or apnea, such as thiamylal sodium should be given at a reduced dosage and, when injected intravenously, should be administered slowly. When intravenous administration of XYLAZINE HCL INJECTION (xylazine) is desired, avoid perivascular injection in order to achieve the desired effect. Studies have shown negligible evidence of tissue irritation, however, following perivascular injection of xylazine. Intracarotid Arterial Injection Should be Avoided. As with many compounds, including tranquilizers, immediate violent seizures followed by collapse may result from inadvertent administration into the carotid artery. Although the reaction with XYLAZINE HCL INJECTION (xylazine) is usually transient and recovery may be rapid and complete, special care should be taken to assure that the needle is in the jugular vein rather than the carotid artery. Bradycardia and arrhythmia in the form of incomplete atrioventricular block have been reported following xylazine administration. Although clinically the importance of this effect is questioned,1,2,3,4 a standard dose of atropine given prior to or following xylazine will greatly decrease the incidence. Sedation for transport is most successful if actual transportation is begun after the full effect of the drug has been reached and the animal's stability is maintained while standing. In addition, it should be noted that animals under the influence of xylazine can be aroused by noise or other stimuli and this may increase the risk of injury. Keep out of reach of children. Warning(s): This drug should not be administered to domestic food-producing animals. Not for use in horses intended for food. Avoid accidental administration to humans. Should such exposure occur, notify a physician immediately. Artificial respiration may be indicated. Side Effects: XYLAZINE HCL INJECTION (xylazine) in horses, used at recommended dosage levels may occasionally cause slight muscle tremors, bradycardia with partial A-V heart block and a reduced respiratory rate. Movement in response to sharp auditory stimuli may be observed. In horses, sweating, rarely profuse, has been reported following administration. ] Trial Data: Safety: XYLAZINE HCL INJECTION (xylazine) is tolerated at 10 times the recommended dose in horses. However, some elevated doses produced muscle tremors and long periods of sedation. References: Available upon request. Presentation: XYLAZINE HCL INJECTION (xylazine) is available in 50 mL multiple dose vials. Iss. 3-00

Concurrent use with chloramphenicol could greatly prolong the sedative and metabolic effect, particularly the GI stasis, resulting in gas colic. Chloramphenicol inhibits the activity of cytochrome 450 which is responsible for catabolising xylazine (also phenylbutazone, barbituates, and others).

Xylazine is contraindicated in animals receiving epinephrine or having active ventricular arrhythmias. It should be used with extreme caution in animals with preexisting cardiac dysfunction, hypotension or shock, respiratory dysfunction, severe hepatic or renal insufficiency, preexisting seizure disorders, or if severely debilitated. Because it may induce premature parturition, it should generally not be used in the last trimester of pregnancy.

Horses have been known to kick out behind rapidly and forcibly after a stimulatory event while sedated with xylazine. This product should not be used alone when you are working around the hind limbs of the horse nor should the horse be approached from behind while sedated. Avoid intra-arterial injection; may cause severe seizures and collapse. The manufacturers warn against using in conjunction with other tranquilizers however it is frequently combined in practice with acepromazine or butorphanol to decrease the kick reflex.

Transient but remarkable decreases in heart rate and missed heart beats often occur when first injected. Sweating and urination is common as the horse recovers from the sedative. 1998 reports suggest care needs to be exercised with xylazine use in horses with colic because of significantly lowered bowel motility for up to 2 and 1/2 hours following administration. The suppression was milder and of lower duration with xylazine but quite profound with detomidine, ...more.

Accidental overdosage generally cause an exacerbation of the toxic effects: cardiac arrhythmias, hypotension, and profound CNS and respiratory depression may occur. Seizures have also been reported after overdoses. Mechanical respiratory support with respiratory stimulants (e.g., doxapram) seen rational for the horse with severe respiratory depression. Epinephrine should NOT be used.

Elective reversal of xylazine sedation with either tolazoline or yohimbine is not without serious risk of idiosyncratic and potentially fatal consequences in the horse as evidenced by clinical reports of drug reaction and possible death resulting from administration of tolazoline or yohimbine to reverse the effects of alpha-2 agonist sedation. There does not seem to be a predisposing factor to these reactions based on the limited number of cases in this series. A clear mechanism for the adverse reactions from the use of tolazoline or yohimbine has not been identified but likely is caused by cardiopulmonary and CNS events.

The recommended dosages for
alpha-2 antagonists in the horse are as follows:

• tolazoline, 4 mg/kg, IV, slowly at a rate of 1 ml/s
• yohimbine, 0.075 mg/kg, IV (off-label use).

To increase the safety of alpha-2 adrenergic antagonists, the following guidelines should be observed.

• IM administration: the reversal agent may be given IM, and this is preferred in all but emergency situations because it decreases the risk for CNS excitement or cardiovascular complications.
• Intravascular administration: administer three separate aliquots equal to one third total IV dose over a 30-min window to prevent sudden cardiopulmonary changes seen with sudden alpha-2 antagonism.

Dosages are dependent on the method of administration and what drugs the xylazine are combined with. Note: the manufacturers state that xylazine should not be used in conjunction with other tranquilizers. However clinically it is often combined with other tranquilizers particularly for working around the rear legs or reproductive work as it is felt it makes kicking less likely.

• 1.1 mg/kg IV; 2.2 mg/kg IM. Allow animal to rest quietly until full effect is reached. (Package Insert; Rompun - Miles)
• Sedative / analgesic for colic: 0.3 - 0.5 mg/kg IV; repeat as necessary (Muir 1987)
• Prior to guaifenesin/thiobarbiturate anesthesia: 0.55 mg/kg IV;
• Prior to ketamine induction: 1.1 mg/kg IV;
• In combination with other tranquilizers (all IV doses):
  • xylazine 0.66 mg/kg; meperidine 1.1 mg/kg
  • xylazine 1.1 mg/kg; butorphanol 0.01 - 0.02 mg/kg
  • xylazine 0.6 mg/kg; acepromazine 0.02 mg/kg

• Level of anesthesia/analgesia
• Respiratory function
• Cardiovascular status (rate, rhythm, BP if possible)
• Hydration status if polyuria present

Xylazine should only be used by individuals familiar with its use.

Several concentrations are available for small animal-ruminant use and for large animals. The form most commonly used in horses is 100 mg / ml: Rompun (Bayer) Gemini (Butler); AnaSed (Lloyd);Sedazine (Fort Dodge) (Rx)

ARCI Class: 3
Detection Time: 24 hrs (Canada) to 72 hrs elsewhere.
SB, TB, and QH Racing: different by state
AQHA: prohibited
AHSA: forbidden
FEI: prohibited

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