Pharmacokinetics of a Single Subcutaneous Extended-Release Buprenorphine (Ethiqa XR) in Healthy Beagles

This study evaluated the pharmacokinetics of an extended-release buprenorphine formulation (Ethiqa XR) in dogs and explored potential sex differences. Twelve healthy intact beagles (6 males and 6 females) received a single subcutaneous injection of Ethiqa XR (0.2 mg/kg). Blood samples were collected up to 168 h post-administration, and plasma buprenorphine concentrations were measured using liquid chromatography-tandem mass spectrometry. Vital signs, sedation, and nausea scores were recorded. Therapeutic plasma concentrations were sustained for approximately 60-90 h in both sexes, depending on the therapeutic threshold used (0.6 or 1.0 ng/mL). Although no significant differences in pharmacokinetics were detected, drug exposure and elimination were greater in females: median peak plasma buprenorphine concentrations (male: 1.6 ng/mL, female: 2.9 ng/mL); median terminal half-life (male: 36.6 h, female: 24.7 h); area under the curve (AUC 0-12 h) (male: 12.8 h*ng/mL, female: 16.9 h*ng/mL); AUC (0-96 h) (male: 94.4 h*ng/mL, female: 137.7 h*ng/mL). Time to maximum concentrations were 24 h in both sexes. Higher buprenorphine concentrations were associated with decreased body temperature and heart rate in both sexes and positively correlated with nausea and sedation scores, but only in females. Ethiqa XR administration resulted in therapeutic plasma concentrations up to 90 h, suggesting it may be an alternative option for post-operative pain control.