Thermal antinociceptive effects after intramuscular administration of high doses of hydromorphone in cockatiels (Nymphicus hollandicus).

Abstract

Objective: To evaluate the thermal antinociceptive effects of hydromorphone hydrochloride administered IM to cockatiels (Nymphicus hollandicus) at higher doses than previously reported.

Methods: 12 adult cockatiels received hydromorphone IM at doses of 1 and 2 mg/kg and an equivalent volume of saline (0.9% NaCl) solution (control treatment) in a masked, randomized, within-subjects complete crossover study. The thermal foot withdrawal threshold (TFWT) was determined at baseline as well as 0.5, 1.5, 3, and 6 hours postinjection. Agitation-sedation scores were also evaluated at each time point prior to delivery of thermal stimulus. The changes in TFWT compared to baseline as well as agitation-sedation scores prior to each TFWT were compared among treatments over time.

Results: 1 bird died during the study for unrelated causes. Hydromorphone at both doses (1 and 2 mg/kg) had a significant difference in foot withdrawal threshold from baseline when compared to the control at the 3-hour postinjection time point. Hydromorphone at 1 mg/kg significantly decreased odds of a bird having higher agitation scores (proportional OR of increase in agitation score of 1, 0.37; 95% CI, 0.14 to 0.96).

Conclusions: Hydromorphone administered IM at doses of 1 and 2 mg/kg had a small but significant thermal antinociceptive effect in cockatiels at 3 hours after drug administration. Hydromorphone at 1 mg/kg demonstrated evidence of mild sedative effects.

Clinical relevance: This study provides evidence that hydromorphone may provide analgesic effects when administered to cockatiels at doses higher than those evaluated in prior studies. Further studies with other types of noxious stimuli, routes of administration, and testing time points are needed to fully evaluate the analgesic effects of hydromorphone in cockatiels.