Evaluation of the Thermal Antinociceptive Effects of Butorphanol Tartrate in American Kestrels (Falco sparverius)
Partial kappa-opioid agonist and mu-opioid antagonists, like butorphanol and nalbuphine, are currently the recommended opioids for acute pain management in psittacines.1-4 Pure mu-opioid agonists, like hydromorphone, also have been evaluated previously in birds with conflicting results,5-9 but they have been shown recently as potential analgesics for American kestrels (Falco sparverius).10 A blinded randomized complete crossover study using foot withdrawal threshold to a noxious thermal stimulus was performed to evaluate the antinociceptive effect and duration of action of butorphanol tartrate. Butorphanol tartrate (1, 3 and 6 mg/kg IM, Fort Dodge Animal Health, KS, USA) and saline solution (0.9% Saline, Hospira Inc., Lake Forest, IL, USA) were evaluated in 15 kestrels. Baseline thermal withdrawal threshold data were generated prior to drug administration then thermal foot withdrawal threshold measurements were obtained at 0.5, 1.5, 3, and 6 hours following butorphanol administration. Kestrels were assigned an agitation-sedation score and monitored throughout the testing period for adverse effects. Butorphanol tartrate caused sex-dependent responses in American kestrels. The increase in mean threshold in females was suggestive of very mild analgesia; however, mild hyperalgesia and agitation, especially at higher dosages, were observed in male kestrels. Butorphanol tartrate might not provide clinically effective analgesia in American kestrels. Further studies with other types of stimulations, formulations, dosages, and routes of administration are needed to fully evaluate the analgesic and adverse effects butorphanol in kestrels and other avian species and its relevance in the clinical setting.
This study was supported by Morris Animal Foundation (grant no. D10ZO-305), Englewood, CO, USA
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