Evaluation of thermal antinociceptive effects after intramuscular administration of methadone hydrochloride to orange-winged Amazon parrots (Amazona amazonica).

OBJECTIVE

To evaluate the thermal antinociceptive effects of methadone after IM administration to orange-winged Amazon parrots (Amazona amazonica).

METHODS

8 Amazon parrots received IM methadone hydrochloride (1, 3, and 6 mg/kg) and saline (0.9% NaCl) solution in a masked randomized, within-subjects, balanced complete crossover experimental design. The thermal foot withdrawal threshold (TFWT) was determined 5 minutes before (baseline) and 0.5, 1.5, 3, and 6 hours after treatment administration. Agitation-sedation scores and other adverse effects were evaluated in the test box at each time point before each TFWT.

RESULTS

Methadone at 6 mg/kg significantly increased TFWT when compared with control by an average of 1.9 ± 0.5 °C accounting for baseline values. Methadone also caused agitation for 1, 3, and 6 mg/kg at 0.5 to 1.5 hours compared to control and increased nausea-like behavior (opening the beak and moving the tongue back and forth) for all doses up to 3 hours posttreatment compared to control. Although ataxia was not significant overall, some birds showed ataxia at 0.5 and 1.5 hours following administration of 6 mg/kg.

CONCLUSIONS

Methadone administered IM to orange-winged Amazon parrots at 6 mg/kg significantly increased TFWT and appears to have a rapid onset and relatively short duration. Agitation and nausea-like behavior were also observed at lower doses.

CLINICAL RELEVANCE: The benefit of rapid onset, potent analgesic effect, and added mechanisms of action to the opioid-mediated analgesia make methadone an added choice for clinical use in this species. However, these doses caused neuroexcitation with agitation and nausea-like behavior, which should be considered in clinical use.