Many procedures that are routinely accomplished in domestic animals with minimal restraint require anesthesia for the welfare and safety of both the zoo animal and veterinarian. Therefore, the chemical immobilization of wild and exotic animals in the zoo setting (as opposed to in the field) is essentially a form of veterinary anesthesia conducted under substantially more difficult circumstances than in a practice setting.1

Situationally, the chemical immobilization of zoo animals involves far more control and predictability of the environment than sedating or anesthetizing the same animals in the field, but it still requires an abundance of caution and planning, as well as the requisite skills and qualified personnel. Although physiological responses during the maintenance of anesthesia are not different in a given species in the zoo (versus in the field), successful induction and recovery require significantly more knowledge and skills.2

While veterinarians in traditional practice settings are typically very well-versed in the action of commonly-used anesthetics and the physiological responses of familiar domesticated species, it can be an ongoing challenge for veterinarians to maintain stocks of the appropriate sedation and anesthetic drugs for animals in the zoo setting.

Medetomidine in the Zoo Setting

Medetomidine (medetomidine hydrochloride), used alone and in combination with other drugs, has been shown to be useful for anesthesia and immobilization in zoo animals.3 Medetomidine is an α-2-adrenoreceptor agonist with sedative and analgesic properties. It is used by veterinarians as both a surgical anesthetic and analgesic. The pharmacological restraint and pain relief provided by medetomidine facilitates handling and aids in the conduct of diagnostic or therapeutic procedures. It also facilitates minor surgical procedures (with or without local anesthesia) and dental care where intubation is not required.

Medetomidine: Pharmacology and Pharmacokinetics

An alpha adrenergic receptor, medetomidine has an alpha-2:alpha-1 selectivity factor of 1620 and, when compared to xylazine, is reportedly 10 times more specific for alpha-2 receptors vs alpha-1 receptors. The pharmacologic effects of medetomidine include: depression of CNS (sedation, anxiolysis), GI (decreased secretions, varying effects on intestinal muscle tone) and endocrine functions, peripheral and cardiac vasoconstriction, bradycardia, respiratory depression, diuresis, hypothermia, analgesia (somatic and visceral), muscle relaxation (but not enough for intubation), and blanched or cyanotic mucous membranes. Effects on blood pressure are variable, but medetomidine can cause hypertension longer than does xylazine. Medetomidine also induces sedation for a longer period than does xylazine. Sedative effects persist longer than analgesic effects.4

After IV or IM injection, onset of effect is rapid (5 minutes for IV; 10-15 minutes for IM). After SC injection, responses are unreliable and this method of administration cannot be recommended. The drug is absorbed via the oral mucosa when administered sublingually in dogs, but efficacy at a given dose may be less than with IM dosing.4

Medetomidine: Warnings

Medetomidine is contraindicated in dogs having the following conditions: cardiac disease, respiratory disorders, liver or kidney disease, shock, severe debilitation, or dogs stressed due to heat, cold, or fatigue.

Dogs that are extremely agitated or excited may have a decreased response to medetomidine; the manufacturer suggests allowing these dogs to rest quietly before administration of the drug. Dogs not responding to medetomidine should not be re-dosed. Use in young or older dogs should be done with caution.

Medetomidine at 5, 10, 20, and 40 micrograms/kg IM reduced tear flow in dogs in a dose dependent manner. Medetomidine 80 micrograms/kg combined with ketamine5 mg/kg mixed in the same syringe administered IM decreased tear production in cats during anesthesia that persisted up to 15 minutes after reversal with atipamezole. Ophthalmic ointment should be used to protect eyes when using this drug.5,6

Adverse effects reported with medetomidine use are essentially extensions of its pharmacologic effects including bradycardia, occasional AV blocks, decreased respiration, hypothermia, urination, vomiting, hyperglycemia, and pain on IM injection.4 Rare effects have also been reported, including prolonged sedation, paradoxical excitation, hypersensitivity, apnea, and death from circulatory failure. One study reports reduced tear flow in dogs in a dose-related manner. However, administration of medetomidine at 5, 10, 20, 40 and 80 micrograms/kg IM did not affect intraocular pressure except at the 80 micrograms/kg. This dose caused a decrease in intraocular pressure hours after administration.7 In cats, even high dose (100 microgram/kg) of medetomidine do not effect intraocular pressure.8

The following drug interactions have either been reported or are theoretical in humans or animals receiving medetomidine and may be of significance in veterinary patients.  

ATROPINE, GLYCOPYRROLATE: The use of atropine or glycopyrrolate to prevent or treat medetomidine-caused bradycardia is controversial as tachycardia and hypertension may result. This is more important when using higher doses of medetomidine (>20 micrograms/kg) and concomitant use is discouraged.

HYOSCINE: One study showed tachycardia and hypertension developed when hyoscine was administered IV or IM before medetomidine in horses.9

OPIOIDS: Enhancement of sedation and analgesia may occur when medetomidine is used concurrently with fentanyl, butorphanol, or meperidine, but adverse effects may be pronounced as well. Reduced dosages and monitoring are advised if contemplating combination therapy.

PROPOFOL: When propofol is used after medetomidine, hypoxemia may occur. Dosage adjustments may be required along with adequate monitoring.

YOHIMBINE: May reverse the effects of medetomidine; but atipamezole is preferred for clinical use to reverse the drug’s effects.
(Plumb’s Veterinary Drugs)

Dosages

When using medetomidine in zoo, exotic and wildlife medicine refer to specific references, including:

a) Zoo Animal and Wildlife Immobilization and Anesthesia, 2nd ed. West, G., Heard, D., Caulkett, N. (eds.). Blackwell Publishing, 2014.

b) Handbook of Wildlife Chemical Immobilization, 3rd Ed. Kreeger, T.J. and J.M. Arnemo. 2007.

c) Fowler’s Zoo and Wild Animal Medicine Current Therapy, Volume 7, Miller, R.E., Fowler, M.E., Saunders. 2011.

d) Exotic Animal Formulary, 5th Ed. Carpenter, J.W., Saunders. 2017.
(Plumb’s Veterinary Drugs)

Where to buy Medetomidine 10mg/ml 

Medetomidine 10mg/ml is available in the U.S. through several pharmaceutical manufacturers and through veterinary custom compounding companies. Medetomidine 0.5 mg/ml injectable by NexGen is indicated for use as a sedative and analgesic to facilitate clinical examinations, clinical procedures, minor surgical procedures not requiring muscle relaxation, and minor dental procedures where intubation is not required.

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

1Nielsen L. Chemical immobilization of wild and exotic animals. Iowa: Iowa State University Press, 1999; 227-281.

2Lewis JCM. Anesthesia of non-domestic cats. Hall, L.W., Taylor, P.M. Anaesthesia of the Cat. London: Bailliere Tindall, 1994; 310-349.

3Vähä-Vahe T. The clinical efficacy of medetomidine. Acta Vet Scand Suppl. 1989;85:151-3. PMID: 2571266.

4Plumb’s Veterinary Drugs.

5Di Pietro S, et al. Effects of a medetomidine-ketamine combination on Schirmer tear test I results of clinically normal cats. Am J Vet Res. 2016;77(3):310-314.

6Kanda T, et al. Temporal effects of intramuscular administration of medetomidine hydrochloride or xylazine hydrochloride to healthy dogs on tear flow measured by use of a Schirmer tear test I. Am J Vet Res. 2016;77(4):346-350.

7Kanda T, et al. Effects of medetomidine and xylazine on intraocular pressure and pupil size in healthy Beagle dogs. Vet Anaesth Analg. 2015;42(6):623-628.

8Malmasi A, Ghaffari MS. Lack of effects of intramuscular medetomidine on intraocular pressure in clinically normal cats. J Feline Med Surg. 2016;18(4):315-317.

9Perotta JH, et al. Hyoscine-N-butylbromide premedication on cardiovascular variables of horses sedated with medetomidine. Vet Anaesth Analg. 2014;41(4):357-364.