Abstract
Butorphanol (Torbugesic-SA®, Fort Dodge Animal Health, Fort Dodge, Iowa 50501) is a commonly administered agent in zoological species due to its analgesic, sedative, and antitussive properties. In addition, the opioid agonist/antagonist can be reversed with naloxone hydrochloride (Narcan, Endo Pharmaceuticals Inc., Chadds Ford, Pennsylvania 19317) or naltrexone hydrochloride (Wildlife Pharmaceuticals, Incorporated, Fort Collins, Colorado 80524). Though other sedatives have been effectively used in cetaceans, butorphanol appears to be a generally safe alternative in cases where midazolam (Versed, Roche Laboratories, Inc., Nutley, New Jersey 07110) alone does not provide adequate sedation.
Over the last two years at SeaWorld Orlando, butorphanol has been used as a sedative in 35 procedures of ten cetaceans, including seven bottlenose dolphins (Tursiops truncatus), one false killer whale (Pseudorca crassidens), and two killer whales (Orca orcinus). In all cases, butorphanol was selected due to its perceived ability to cause deeper sedation in cetaceans than midazolam alone. Of the ten animals administered butorphanol, five were sedated more than once and three were sedated seven or more times. Two bottlenose dolphins were bronchoscoped biweekly for several months to monitor response to treatment for severe pneumonia, and one killer whale was sedated twice daily for four days for oral speculum placement and orogastric intubation. Other procedures in which butorphanol sedation was administered included gastric endoscopy, oral surgery/cryotherapy, and tooth extraction. Whereas previous attempts to adequately sedate a 500 kg false killer whale for a dental procedure had failed with midazolam, intramuscular butorphanol administration and local gingival 2% lidocaine infusion provided enough sedation and analgesia to allow safe tooth extraction.
Butorphanol dosages of 0.05-0.13 mg/kg (median/mean 0.07 mg/kg) were administered intramuscularly in each animal. Lower dosages were given to cetaceans considered less physiologically or medically stable than normal. Butorphanol dosages as high as 0.2 mg/kg have been used in a killer whale at SeaWorld San Antonio. In all but four sedations at SeaWorld Orlando, the animals appeared behaviorally unchanged or mildly sedated while swimming the first 20-25 minutes after injection. Once removed from the water, most of these same cetaceans appeared calm or showed mild depression in their respiratory rates, but were responsive to stimulus. Cetaceans have been effectively reversed with intramuscular administration of naltrexone at a dose of 0.005 mg/kg.
Four excitatory reactions were recorded between two individuals. One bottlenose dolphin, a dominant female with known aggressive tendencies when restrained, was believed to override butorphanol's sedative effects on two attempts with 0.05 mg/kg and 0.13 mg/kg dosages, respectively. The second bottlenose dolphin, which had been previously sedated with similar dosages of 0.05-0.07 mg/kg for nine bronchoscopies, showed marked agitation, occasional chuffing, and an increased respiratory rate within 15 minutes of butorphanol administration on two separate occasions. These behavioral changes ceased within five minutes of 0.3 mg/kg intramuscular naltrexone reversal. It was suspected that an adverse drug interaction occurred between the butorphanol and aminophylline, with which the dolphin was being treated for pneumonia.
To date, butorphanol has shown to be efficacious in cetaceans due its sedative and reversible properties. Study is ongoing to investigate further aspects of butorphanol sedation, but preliminary findings suggest that intramuscular butorphanol at a dosage of 0.045-0.1 mg/kg can be used safely in many cetaceans. Close observation and physiological monitoring of the butorphanol-sedated cetacean is recommended in case of excitatory or adverse reactions.
Acknowledgements
The authors would like to thank the SeaWorld Animal Care staff, Training staff, and veterinary technicians for their assistance with these cases, as well as curatorial staff for their support. We would also like thank Dr. James McBain for sharing his experience and expertise regarding anesthesia in cetaceans.