Pharmacokinetics and pharmacodynamics of intramuscular dexmedetomidine in dogs

OBJECTIVE To determine the pharmacokinetics and pharmacodynamics of dexmedetomidine after IM administration in dogs.ANIMALS 6 healthy adult purpose-bred dogs (3 males, 3 females) with a mean +/- SD body weight of 25.2 +/- 1.8 kg.PROCEDURES Each dog received 10 mu g/kg dexmedetomidine, IM. Heart rate and respiratory rate were counted via cardiac aus- cultation and visual assessment of chest excursions. Sedation was assessed utilizing 2 sedation scoring systems. Plasma concentrations were determined using ultra performance liquid chromatography-mass spectrometry. Plasma concentrations versus time data after IM dexmedetomidine were analyzed using noncompartmental analysis for extravascular administration.RESULTS Over the first 2 hours following IM injection of dexmedetomidine, plasma concentrations fluctuated in each dog. The geometric mean (range) maximum plasma concentration was 109.2 (22.4 to 211.5) ng/mL occurring at 20.5 (5 to 75) minutes, and the mean half-life was 25.5 (11.5 to 41.5) minutes. Heart rate was significantly lower than baseline from 30 minutes to 2 hours postdexmedetomidine administration, and respiratory rate was significantly lower than baseline from 45 minutes to 1.75 hours. Dogs were significantly more sedated from 30 minutes to 1.5 hours post- dexmedetomidine administration. Median time to onset of sedation was 7.5 minutes (range, 2 to 10 minutes), and median time to peak sedation was 30 minutes (range, 15 to 60 minutes).CLINICAL RELEVANCE Variations in plasma concentrations occurred in all dogs for the 2 hours postinjection of dexmedetomidine at 10 mu g/kg, IM. This was likely due to alterations in absorption due to dexmedetomidine-induced local vasoconstric- tion. Despite variable plasma concentrations, all dogs were sedated following IM dexmedetomidine administration.