Buprenorphine is a partial μ agonist opioid used for analgesia in dogs. An extended-release formulation (ER-buprenorphine) has been shown to provide effective analgesia for 72 hr in rats and mice. Six healthy mongrel dogs were enrolled in a randomized, blinded crossover design to describe and compare the pharmacokinetics and pharmacodynamics of ER-buprenorphine administered subcutaneous at 0.2 mg/kg (ER-B) and commercially available buprenorphine for injection intravenously at 0.02 mg/kg (IV-B). After drug administration, serial blood samples were collected to measure plasma buprenorphine concentrations using liquid chromatography/mass spectrometry detection. Heart rate, respiratory rate, body temperature, sedation score, and thermal threshold latency were recorded throughout the study. Median (range) terminal half-life, time to maximum concentration, and maximum plasma concentration of ER-buprenorphine were 12.74 hr (10.43-18.84 hr), 8 hr (4-36 hr), and 5.00 ng/ml (4.29-10.98 ng/ml), respectively. Mild bradycardia, hypothermia, and inappetence were noted in both groups. Thermal threshold latency was significantly prolonged compared to baseline up to 12 hr and up to 72 hr in IV-B and ER-B, respectively. These results showed that ER-buprenorphine administered at a dose of 0.2 mg/kg resulted in prolonged and sustained plasma concentrations and antinociceptive effects up to 72 hr after drug administration.

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