Single-dose pharmacokinetics and bioavailability of a novel extended duration transdermal buprenorphine solution in cats.

A novel transdermal buprenorphine solution (TBS) was developed for evaluation in order to make available an extended duration opioid analgesic for cats. Healthy adult cats were administered a single TBS dose of 10 mg (1.57-4.35 mg/kg), 30 mg (4.72-13.0 mg/kg), or 50 mg (7.87-21.7 mg/kg) (4 cats per group) applied topically to the unclipped dorsal cervical skin and plasma buprenorphine concentrations were evaluated through 7 days. To determine the absolute bioavailability of TBS, healthy cats were administered single TBS dose of 20 mg (3.33-4.76 mg/kg) or 0.05 mg (0.008-0.011 mg/kg) IV buprenorphine (6 cats per group). The mean ± standard deviation maximum plasma buprenorphine concentrations (C ) were 10.5 ± 6.28, 18.6 ± 8.68, and 22.5 ± 4.47 ng/ml following 10, 30, and 50 mg doses, respectively, with the time of C occurrence (t ) typically occurring at 2-12 h post-dosing. Mean plasma buprenorphine terminal half-lives ranged between 78.3 and 91.2 h. Increasing the dose threefold and fivefold from the 10 mg dose increased the exposure by 2.8- and 3.6-fold, respectively, indicating that plasma buprenorphine exposure increased in a less than proportional manner at doses >30 mg. Transient sedation, mydriasis, and euphoria were observed within 4 h post-dosing. Mean rectal temperatures were increased 0.6-0.9°C greater than baseline (37.4-37.8°C) through 168 h post-dosing. The absolute bioavailability was 16.0% (90% CI: [11.8%-21.7%]). Flip-flop pharmacokinetics were observed with a terminal elimination half-life of 0.82 ± 0.13 and 64.9 ± 15.0 h for IV buprenorphine and 20 mg of TBS, respectively. A single administration of TBS over a range of doses resulted in extended plasma buprenorphine concentrations and opioid physiological and behavioral effects.