The chemical immobilization of wildlife species is a form of veterinary anesthesia conducted under difficult circumstances.1 Anesthesia plays an important role in wildlife veterinary medicine, since the majority of the procedures carried out involve chemical restraint techniques.1 Veterinarians in wildlife medicine must administer anesthetic drugs effectively, using varied delivery systems. There are different approaches to administering drugs in chemical restraint procedures: oral, hand-held injection, pole syringe and darts. In cooperative animals, hand-held injections or the pole-syringed administration are usually the delivery routes of choice.

The ideal immobilization drug formulations for wild and exotic animals will have a wide safety margin, small volume for delivery, and is fully reversible; thus, a small volume will facilitate rapid administration especially if remote delivery systems are used.1,2 The refinement of drug formulations has been a dedicated concern of wildlife managers and veterinarians over the last several decades, and the premixed formulas available today are far superior to the on-the-fly drugs and formulations used in years past. Many formulations are also available with their ideal reversal agents, an indispensible component in the field. 

The MK Kit

The MK Kit by NexGen Pharmaceuticals is a premixed formulation developed to provide veterinarians and wildlife handlers with a field-tested immobilization anesthesia option that can be effectively used to immobilize a broad range of exotic animal species. Medetomidine (5mg/ml) provides superior pain relief and muscle relaxation to other compounds employing α-2 adrenergic agonists, with Ketamine HCL (150 mg/ml) supplying an effective paralytic. In combination, the two provide safe, smooth induction times and excellent recovery results. Atipamezole, a synthetic α2-adrenergic antagonist, is provided in the MK Kit as a reversal agent. 

Medetomidine 

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 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. Medetomidine also induces sedation for a longer period than does xylazine. Sedative effects persist longer than analgesic effects.4

Ketamine

Ketamine is a dissociative general anesthetic and an NMDA-receptor antagonist. It has been FDA-approved for use in humans, sub-human primates, and cats, although it has been used in many other species.1,4 Ketamine is used to induce general anesthesia and as a constant rate infusion to provide analgesia and decrease the amount of inhalant used to maintain a surgical plane of anesthesia. Ketamine can inhibit NMDA receptors in the CNS and can decrease the wind-up pain effect. There is increasing interest in using it to prevent exaggerated pain associated with surgery or chronic pain states in animals.1

Ketamine is a rapid-acting general anesthetic that has significant analgesic activity and a relative lack of cardiopulmonary depressant effects in healthy animals. It is thought to induce both anesthesia and amnesia by functionally disrupting the CNS through over-stimulating the CNS or inducing a cataleptic state. Ketamine also interacts with opioid and monoaminergic receptors, which contributes to the antinociceptive effects of this drug.3,4

Atipamezole (Reversal Agent)

Atipamezole is a synthetic α2-adrenergic antagonist that was developed to reverse the actions of compounds such as medetomidine and dexmedetomidine. Due to its efficacy compared to other drugs in its class, dexmedetomidine is currently being evaluated as an adjunct to anesthesia in humans. Compared with clonidine, dexmedetomidine is approximately 10 times more selective toward the α2-adrenoceptor and acts as a full agonist in some pharmacologic test models in which the former displays only partial agonism.2,4 Atipamezole is commonly used to treat horses and dogs, with extra-label use for other species. It is thought that this drug could be useful for reversal of other alpha-2 adrenergic agonists as well (eg, amitraz, xylazine, clonidine, tizanidine, brimonidine), but little information in this area is available at present.4

Delivery and Recommendations

For those who are new to utilizing MK to manage their exotic animals, it is important to understand the level of anesthesia administered with Medetomidine/Ketamine sedation. MK is a deep sedation, not to be confused with other sedations that are moderate.

The preferred route for the administration of an immobilizing drug by remote delivery is via intramuscular injection. The aim is to hit the animal in a specifically-selected site, causing injection into vascular tissue and facilitating rapid absorption of the drug. Not all areas of an animal's body are equally well-suited for injection by remote delivery; thus, the injection site should be carefully chosen.

The neck is generally a suitable site for large animals with muscular necks. Care should be taken to avoid hitting the jugular vein, the upper neck and the head. The ideal injection site is the trapezius muscle mass at the upper base of the neck. This injection site is suitable for species such as elk, moose, buffalo, bear, the equids and larger antelopes, rhinoceros, hippopotamus and elephant (if the ears can be avoided). Animals with slender necks, such as gazelle, gerenuk, giraffe and impala should not be darted in this area.

The shoulder is a suitable injection site in many larger species. This region is well-muscled, presenting a flat, perpendicular target. It is surrounded by relatively resilient areas and presents a fair-sized target in animals that are robust enough to be darted with remote delivery equipment.

To prevent the needle from becoming embedded in cartilage, the upper end of the scapula should be avoided. In sensitive species, the sight and smell of a dart in the shoulder may cause panic and flight. Some carnivores will destroy the dart by pulling it out with their teeth. The shoulder is not a suitable injection site for smaller species, due to their lesser size and limited muscle mass.

Where to buy the MK Kit

The MK Kit is available through NexGen Pharmaceuticals. Please consult your veterinarian prior to beginning any treatment regimen.

NOTE: This product is listed as a U.S. Drug Enforcement Administration (DEA) Schedule CIII Controlled Substance.

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

1West, G., et. al. Zoo Animal and Wildlife Immobilization and Anesthesia, Second Edition, John Wiley & Sons, Inc., July 2014.

2Arnemo, Jon & Kreeger, Terry. (2018). Handbook of Wildlife Chemical Immobilization, 5th Ed.

3Nielsen, L. Chemical immobilization of wild and exotic animals, Ames: Iowa State University Press, 1999.

4Plumb’s Veterinary Drugs.