Oxycodone, a full mu opioid receptor agonist prescribed for moderate-to-severe pain in people, could provide outpatient analgesia for dogs with post-operative or cancer pain. To determine the pharmacokinetic profile and physiological side effects of a single oral (PO) dose, five healthy, 2-year-old, castrated male hounds were administered a standard amount of food, with or without immediate-release oxycodone (1 mg/kg), in random order, separated by 1 month. At intervals between 0.25 and 8 h later, blood was sampled to measure plasma oxycodone concentration using ultra high-pressure liquid chromatography with mass spectrometry detection, and vital signs were evaluated. Pharmacokinetic variables were estimated using noncompartmental analysis. Maximum plasma concentration (Cmax) was 58.6 (39.3, 61.6) ng/mL, time to maximal plasma concentration (tmax) was 1.5 (0.5, 2.0) h, elimination half-life (t1/2el) was 2.6 (2.0, 6.7) h, area under the curve from time 0 to last measurement (AUC0-t) was 236.1 (204.6, 256.0) ng-h/mL, and mean residence time (MRT) was 3.9 (3.4, 9.8) h. Computer simulations using the calculated pharmacokinetic data predicted that 1 mg/kg PO every 6 h would achieve peak (Cmax) and trough (minimum plasma concentration, Cmin) of 69.4 (60.8, 74.6) and 17.0 (15.5, 46.7), respectively, at steady state. Assuming minimum effective analgesic concentration is similar in humans and dogs (~25 mg/mL), therapeutic concentrations were achieved, but administration more frequently than every 6 h would be necessary. Oxycodone produced a significantly lower rectal temperature 1 and 4 h after administration.
Keywords: dog; oral; oxycodone; pharmacodynamics; pharmacokinetics.
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