Plasma concentrations of buprenorphine after epidural administration in conscious cats

Buprenorphine plasma concentrations were measured after administering buprenorphine (20 μg/kg) into the lumbosacral epidural space of conscious cats chronically instrumented with an epidural catheter. Blood was collected from a jugular vein before injection and 15, 30, 45 and 60 min and 2, 3, 4, 5, 6, 8, 12 and 24 h after administration. Plasma buprenorphine concentrations were measured using ELISA. Background concentration (before injection) was 1.27 ± 0.27 ng/mL (mean ± SD). Including background concentration, the mean peak plasma concentration was obtained 15 min after injection (5.82 ± 3.75 ng/mL), and ranged from 3.79 to 2.20 ng/mL (30 min–3 h), remaining between 1.93 and 1.77 ng/mL (4–12 h), and declined to 1.40 ± 0.62 ng/mL at 24 h. Elimination half-life was 58.8 ± 40.2 min and clearance 56.7 ± 21.5 mL/min. Results indicate early rapid systemic uptake of buprenorphine from epidural administration with plasma concentrations similar to using buccal or IM routes by 15 min postinjection.