Alpha 2-adrenergic Agonists

These compounds are non-narcotic sedatives providing good analgesia and muscle relaxation. They are commonly used in veterinary medicine but are not used in human medicine. These drugs are extremely useful on their own but find their most common use in combination with anesthetic agents like ketamine or with the opioids used in wildlife capture (carfentanil and etorphine) where they temper the bad side effects notable with these other compounds. In addition, xylazine offers some synergistic action with these other compounds thus reducing the required dose.

CNS depression occurs via binding to and stimulating presynaptic alpha 2-adrenergic receptors of the CNS and peripherally. This decreases norepinephrine release centrally and peripherally resulting in a decrease in sympathetic outflow and a decrease in circulating catecholamines and other stress-related substances. For sedative action we are most interested in the receptors located in the central nervous system; however, you must recognize that alpha-2 receptors are located throughout the body and use of these drugs produce profound effects on other organ systems (see side effects below). There is a wide species variation in optimum dosage. For example, most bovids are very sensitive and require doses in the range of 0.08-0.1 mg/kg whereas equids and cervids are less sensitive and require doses in the range of 0.1-2mg/kg. It is absolutely crucial that you check published dose rates for the species in question before using these drugs. Sedation or immobilization occurs within 3-5 minutes after IV injection or 10-15 minutes after IM. Analgesia lasts 15-30 minutes but the sleep-like state may last 2 hours (do not perform painful procedures after 30 minutes).

 

Legal:

Prescription drug

 

Indications:

Excellent sedative action in many species with brief (up to 20 minutes) analgesia. Synergistic activity occurs when used in combination with anesthetics.

 

Side effects:

Xylazine is probably the most misused drug with many people ignoring the serious side effects. Although relatively safe with a wide margin of safety in many species it can produce life threatening side effects that are not readily apparent without proper monitoring of the anesthetized/immobilized animal. Now that xylazine is relatively inexpensive there is a tendency to "give a little extra". The cost of medetomidine keeps people a little more responsible. DO NOT INDISCRIMINANTLY PULL EXTRA DRUG INTO THE SYRINGE OR "TOP OFF" THE DART WITH THIS DRUG!

Suppresses insulin release thereby raising plasma glucose concentration and may cause glycosuria. Reduces gastrointestinal motility and may cause bloating in ruminants. Causes vomiting in canids and felids. Can produce profound bradycardia (reduced heart rate); increased cardiac sensitivity to catecholamines; marked decease in cardiac output and, although there may be a transient increase in blood pressure, it rapidly drops due to a decrease in CNS sympathetic outflow. Loss of thermoregulation with a tendency to become hyperthermic.

 

Absorption, Fate, and Distribution:

Drug is rapidly absorbed after intramuscular or subcutaneous injection. It is rapidly metabolized in the liver and excreted in the urine and bile. Many of the metabolites are active.

 

Contraindications:

Rutting muskox, caribou and reindeer bulls are exquisitely sensitive to these drugs. Use with extreme caution.

Generic Name

Common Trade Names

Description

xylazine

Xyla-Ject

TranquiVed

Cervizine

Rompun (no longer available)

Xylazine is commercially available in 2 concentrations: 20mg/ml (2%) and 100mg/ml (10%). ALWAYS CHECK THE LABELING!! Rompun was the only trade name available for many years, until generic versions were permitted. Therefore, this drug is often mistakenly referred to as Rompun even though this trade name has not been available for years.

detomidine

Dormosedan

Detomidine was marketed in the early 1990's for horses. This drug is reputably more potent than xylazine; however, in our hands in muskoxen and caribou, this drug shows no real clinical advantage over xylazine. It is more expensive than xylazine.

medetomidine

Domitor

Zalopine (Europe)

Medetomidine is a new alpha 2-agonist that has great potential in laboratory animal anesthesia and wildlife immobilization. This drug is considerably more potent then xylazine. It is currently available from Pfizer in a 1mg/ml preparation which is useful for small animals. A 10mg/ml concentration available in Europe and currently under an investigational new animal drug license in the US has great promise to replace xylazine. Because medetomidine has 10 times the selectivity for alpha 2-receptors, use only atipamezole (Antisedan) for reversal (see alpha 2-antagonists).

We have successfully used medetomidine with ketamine for surgical anesthesia in mice; however, response seems to vary somewhat between strains. Reversal with atipamezole.

 

Last modified on Saturday April 13, 2002 10:17 AM by John Blake