Objective—To determine the pharmacokinetics of buprenorphine hydrochloride after IM and IV administration to American kestrels (Falco sparverius).

Animals—13 healthy 3-year-old captive-bred American kestrels.

Procedures—Buprenorphine hydrochloride (0.6 mg/kg) was administered IM to all birds. Blood samples were collected at 9 times, ranging from 5 minutes to 9 hours after drug administration. Plasma buprenorphine concentrations were measured by use of tandem liquid chromatography–mass spectrometry. Pharmacokinetic parameters were determined by use of least squares linear regression and noncompartmental analysis of naïve pooled data. After a washout period of 2 weeks, the same dose of buprenorphine was administered IV to all birds and blood samples were collected at the same times after drug administration.

Results—Maximum plasma buprenorphine concentration was achieved within 5 minutes after IM administration. For IM administration, bioavailability was 94.8% and elimination half-life was 92.1 minutes. For IV administration, steady-state volume of distribution was 4,023.8 mL/kg, plasma clearance was 49.2 mL/min/kg, and elimination half-life was 105.5 minutes.

Conclusions and Clinical Relevance—Buprenorphine was rapidly absorbed, and bioavailability was good after IM administration to American kestrels. Plasma buprenorphine concentrations were > 1 ng/mL for 9 hours after both IM and IV administration. These results, in combination with those of a pharmacodynamic study, suggested that the analgesic effects of buprenorphine could last at least 6 to 9 hours in this species. Further investigations of the duration of analgesic effects, multiple-dose protocols, and potential adverse effects of buprenorphine are warranted in American kestrels and other raptors.