Theodore H. Stanley, MD, Professor of Anesthesiology
Chemical immobilization of wild ungulates has advanced dramatically in the last decade. Whereas in the past, drugs used to immobilize wild ungulates often resulted in an enormous stress to the animals because of long chases and relatively impotent drugs that took a long time for onset of activity, drugs now available are much more rapid acting and extremely effective. Carfentanil and more recently A-3080, a new sufentanil-like potent opioid, can reliably immobilize animals in less than five minutes and often less than three minutes from the time of dart impact. A-3080 is the most recent of these compounds which is undergoing its final clinical evaluations in Rocky Mountain elk (Cervus elaphus) in the western part of the United States. Down times of less than 3 minutes are reliable and the drug has a short enough duration of action that most any opioid reversal agent will obviate post immobilization renarcotization. A-3080 has been studied with the new opioid antagonist nalmefene, which has a duration of action of 8 hours. Thus, the combination ensures that there will be no renarcotization. In more than 300 animals studied to date, not a single animal has renarcotized after use of A-3080. The studies were undertaken in the outdoor research facility of the Utah Division of Wildlife Resources near Logan, Utah in trapped wild elk. The animals are studied following administration of measured doses of the opioids after vital signs and weight are obtained with the elk in a squeeze cage.
The success of A-3080 in elk and other ungulates and its close chemical relationship to sufentanil has been a stimulus for human investigators to evaluate the immobilizing capacity of sufentanil in man. Studies have been done in human volunteers and have suggested that use of darts of sufentanil may be effective as a “less than lethal” technique for immobilization of fleeing felons. The next study, which will begin shortly in the human volunteer laboratories at the University of Utah in Salt Lake City, will incorporate a mixture of nalmefene (recently approved for opioid antagonism in humans) plus sufentanil. The objective is that reasonably high doses of sufentanil administered with nalmefene will allow rapid immobilization and minimize the likelihood of respiratory depression.