A Mixture of Butorphanol, Azaperone, and Medetomidine for the Immobilization of American Beavers (Castor canadensis)

Abstract

A total of 58 American beavers ( Castor canadensis) was immobilized with butorphanol, azaperone, and medetomidine (BAM) for the purpose of health assessments, sex determination, and placement of very high-frequency tail transmitters in a subset of animals. Isoflurane gas anesthesia was available to aid with induction when needed, and all animals received supplementary oxygen. Thirty-one beavers immobilized with a mean (SD) dose of 0.65 (0.15) mg/kg butorphanol, 0.22 (0.05) mg/kg azaperone, and 0.26 (0.06) mg/kg medetomidine did not require supplemental isoflurane during induction and the mean induction time was 8 min (range: 3-21 min). This dose was equivalent to 0.024 (0.005) mL of BAM per kilogram. A total of 29 beavers that were immobilized with a mean (SD) of 0.51 (0.07) mg/kg butorphanol, 0.17 (0.02) mg/kg azaperone, and 0.2 (0.03) mg/kg medetomidine needed supplementary isoflurane at 5% and 5 L/min for <1 min to induce full anesthesia. In none of the beavers did BAM alone provide sufficient depth of anesthesia to drill a hole in the tail for transmitter placement, and supplementary isoflurane was administered to reach a sufficient level of analgesia for the procedure. The beavers were reversed with 5 mg of atipamezole per milligram of medetomidine and 1 mg of naltrexone per milligram of butorphanol. No adverse effects or mortalities were observed. Butorphanol-azaperone-medetomidine can be considered safe for use in American beavers for minor procedures.

Butorphanol–Azaperone–Medetomidine for the Immobilization of Rhesus Macaques (Macaca mulatta)

“…These findings, with the exception of hypotension, were consistent with those reported in previous studies. 26,33,34,43,45,46,49,60,61 Individual doses of butorphanol and medetomidine for the 16-and 24-µL/kg BAM doses were higher than published recommendations for sole agent and multiagent administration (butorphanol, 0.05 to 0.2 mg/kg IM; medetomidine, 0.01 to 0.2 mg/kg IM). 3,[7][8][9]21,27,48,52 The doses administered in the current study were more than 4 times the recommended dose of butorphanol and twice that of medetomidine.…”

“…The initial hypoxemia observed prior to oxygen supplementation is consistent with results reported in prior BAM studies involving white-tailed deer, 33,34,49 Rocky Mountain elk, 60 blesbok, 45 and beavers. 43 In addition to the lack of oxygen supplementation, 2 key factors likely contributed to the low S p O 2 values obtained during the initial readings in the current study: peripheral vasoconstriction and the use of pulse oximetry. Vasoconstriction is attributed to the agonistic effects of medetomidine on peripheral α 2 -adrenergic receptors in vascular smooth muscle, resulting in reduced tissue perfusion.…”

“…16,32 The hypotension that occurred in 5 macaques in our study was previously reported in blesbok; however, only 4 of the 9 cited BAM studies assessed blood pressure. 26,33,34,43,45,46,49,60,61 The significant decrease in MAP over time was expected, given the high doses of medetomidine administered, because hypotension is a reported side effect of this drug. 9,38,50 Interestingly, although there are no reports of azaperone use in macaques, this drug may have contributed to the cardiovascular effects observed during our study.…”

“…Developed in 2003 as an alternative to ultrapotent opioids, a combination of butorphanol tartrate (27.3 mg/mL), azaperone tartrate (9.1 mg/ mL), and medetomidine hydrochloride (10.9 mg/mL; BAM) has been used for the immobilization of a wide range of wildlife species. These species include white-tailed deer (Odocoileus virginianus), 33,34,49 Nubian ibex (Capra nubiana), 26 Rocky Mountain elk (Cervus canadensis nelsoni), 60 blesbok (Damaliscus pygorgus phillipsi), 45 American beavers (Castor canadensis), 43 black bears (Ursus americanus), 61 and African lions (Panthera leo). 46 In addition, these drugs-butorphanol, an opioid agonist-antagonist with analgesic (variable), antitussive, and antiemetic properties; azaperone, a butyrophenone tranquilizer with antipsychotic, sedative, and antiemetic properties; and medetomidine, a potent α 2 adrenergic agonist sedative with analgesic, anxiolytic, and muscle-relaxant properties-are used individually in a wide variety of animal species.…”

“…Reported side effects of BAM include nonlife-threatening cyanosis, hypoxemia, bradycardia, bradypnea, as well as rare, mild twitching and muscle tremors. 26,33,34,43,45,46,49,60,61 Given the immobilization success and minimal health effects reported for other species, the goal of the current study was to explore the use of BAM in rhesus macaques (Macaca mulatta). The objectives were to 1) establish a minimal dose that achieves 45 min of chemical immobilization and maintains physiologic values according to predefined thresholds; 2) characterize dose-dependent changes in physiologic values and anesthetic depth over time; 3) assess induction and recovery quality and duration; and 4) document side effects.…”