Comparison of sedation and mechanical antinociception induced by intravenous administration of acepromazine and four dose rates of dexmedetomidine in donkeys.

OBJECTIVE: To assess and compare the sedative and antinociceptive effects of four dosages of dexmedetomidine in donkeys.

STUDY DESIGN: Randomized, controlled, crossover, Latin-square, blinded study.

ANIMALS: Six healthy, castrated, adult, standard donkeys.

METHODS: Dexmedetomidine (2, 3, 4 and 5 μg kg-1 ; D2, D3, D4 and D5), acepromazine (0.1 mg kg-1 ) and saline were administered intravenously to each donkey and a 1 week interval was allowed between successive trials on each animal. Sedation scores (SS) and head heights above ground (HHAG) were used to assess sedation and mechanical nociceptive threshold (MNT) testing to assess antinociception over 120 minutes post-treatment. Areas under the curve (AUC) for 0-30, 30-60 and 60-120 minutes were computed to compare the effect of treatments.

RESULTS: SS-AUC0-30 values were larger for D4 and D5, and SS-AUC30-60 values were larger for D5 than for saline. All dexmedetomidine treatments produced lower HHAG-AUC0-30 and HHAG-AUC30-60 values, and acepromazine produced lower HHAG AUC60-120 values than did saline. For MNT, D3, D4 and D5 increased AUC0-30 and AUC30-60 values compared with saline and also AUC0-30 values compared with D2 and acepromazine. Smaller MNT-AUC30-60 values were obtained with D2 than with D4 and D5, with D3 than with D5, and with acepromazine than with D4 and D5.

CONCLUSIONS AND CLINICAL RELEVANCE: Dexmedetomidine induced sedation and dosage-dependent mechanical antinociception. Larger dexmedetomidine dose rates were required to induce antinociception than sedation. Furthermore, the antinociception induced by dexmedetomidine was of shorter duration than its sedation. For minor painful procedures on standing donkeys, D5 may be clinically useful to provide sedation and analgesia.