Opioid Agents

Etorphine (M99®, Immobilon®)
Etorphine is a highly potent analgesic, up to 10,000 times the potency of morphine.  It possesses similar pharmacologic effects as morphine.  It has been used in a wide range of species and is especially effective in bighorn sheep, elk, deer, bison, equids, elephants, and rhinoceri.  Relfex vomiting, common with morphine, is rare with etorphine, although passive regurgitation can occur.  Fatal hyperthermia may occur with etorphine, especially if the animal has been chased or is highly excited.
 
Diprenorphine (M50-50®) is the preferred antagonist for accidental overdose in wild animals.  (The preferred antidote to accidental overdoses in humans is naloxone (Narcan®).)  It is a narcotic agonist/antagonist.  Therefore, administration will reverse the effects of etorphine, causing the animal to awaken and potentially become defensive.  Since diprenorphine may exert agonist activity, the antidote of diprenorphine overdose is naloxone.

Due to its high potency and potential for fatal accidental overdose, etorphine is generally dyed red, so that it and anything with which it comes in contact may be readily identified.

Carfentanil (Wildnil®)
Carfentanil is also an opioid agonist.  It is 15,000-20,000 time as potent as morphine and is used in a wide range of species.  The antidote for carfentanil overdose is naloxone at a dose of 80-100 times the total dose of carfentanil or diprenorphine at 7 times the carfentanil dose.
A-3080
A-3080 is an investigational opioid agonist that possess a high degree of potency but has a greater therapeutic index than etorphine or carfentanil.  Early clinical trials have indicated that it is safer to use and produces comparable results as the previous agents at equipotent doses.
 
Other narcotic agonists used in exotic animal practice include nalorphine and fentanyl (in combination with droperidol).

Tiletamine and Zolazepam (Telazol®)
Tiletamine is also a dissociative anæsthetic agent that, when used alone, produces analgesia and cataleptoid anæsthesia plus convulsive seizures.  The addition of the benzodiazepine zolazepam eliminates the seizure that tiletamine alone would produce.  The combination produces a state of general anæsthesia but eyelids remain open and corneal, palpebral, laryngeal, pharyngeal, pedal, and pinnal reflexes persist.

Ketamine and xylazine are also used in exotic animals.  Yohimbine (Yobine®, Antagonil®) is used as a specific antidote for xylazine overdose.  Yohimbine is a naturally occurring alpha-adrenergic blocker that acts as a pharmacologic antagonist for xylazine.  Moose do not respond to yohimbine reversal of xylazine-induced sedation.

Succinylcholine, Diazepam, Acepromazine and Azaperone are also used in exotic animals.  Specifically, azaperone (Stresnil®) is used in combination with narcotics to enhance their potency and balance their tendency to cause excitation during absorption.  It is especially useful in red deer and bighorn sheep, however it can cause capture myopathy (muscle damage) when administered following a chase.

Long-Acting neuroleptics (LANs)

LANs or depot tranquilising agents are used as aids in adapting, taming, and training wild animals for zoos or translocation.  Specific LANs that are employed in exotic animals include Zuclopenthixol acetate (Clopixol-Acuphase®), Perphenazine enanthate (Trilafon LA®), and Pipothiazine palmitate (Piportil Depot®).  The use of these agents has greatly reduced the mortality associated with translocation in Africa.

Specific indications include 1) adapting recently captured animals to boma, corral, or pen confinement by reducing anxiety and preventing aggression and self-inflicted trauma, 2) calming animals prior to and during transport/translocation and reducing stress related to a new environment following translocation, 3) controlling animals that are dominant and aggressive, especially adult males, and 4) calming animals for treatment and hospitalisation.

Good results have been observed in waterbuck, bushbuck, giraffe, impala, and black rhinoceros.  Extrapyramidal side effects may occur but may be minimised by the administration of 10-20 mg of biperiden (Akineton®).  NOTE that since these drugs are administered as a depot form, onset of action is relatively slow and the desired effects may not be observed for up to 3 days.