A Pharmacokinetic and Efficacy Study of FDA-Indexed Pharmaceutical-Grade Extended-Release Buprenorphine and Compounded Sustained-Release Buprenorphine in African Green Monkeys (Chlorocebus aethiops)

Compounded sustained-release buprenorphine (SRB) has historically been used at our institution for postoperative analgesia in African green monkeys (AGMs), but it is not FDA approved and lacks species-specific data. With the recent FDA indexing of pharmaceutical-grade extended-release buprenorphine (EXR; Ethiqa XR; Fidelis), we aimed to compare the pharmacokinetic (PK) profile using serial plasma sampling up to 96 hours and postoperative analgesic efficacy of EXR compared with SRB. A total of 10 AGMs (n = 5 per test article) received 0.2 mg/kg SC of either EXR or SRB to complete the PK study. For the efficacy study, 20 animals (n = 10 per test article) were monitored for 3 days postoperatively after EEG telemetry surgery with femoral artery catheterization for behavioral indicators of pain and adverse effects. Plasma buprenorphine levels were analyzed using liquid chromatography-tandem mass spectrometry. PK study observations included appetite, fecal output, and injection site reactions. Both formulations achieved plasma concentrations above the presumed therapeutic threshold (0.1 ng/mL) for up to 96 hours. SRB produced higher mean plasma levels at early time points (30 minutes, 4 hours), but the overall PK profiles were similar. Injection site reactions were minimal and resolved spontaneously. For the efficacy assessment, clinical observations were evaluated using a postoperative score sheet. No significant differences were observed in postoperative pain scores between groups. Both EXR and SRB at 0.2 mg/kg SC provided sustained therapeutic plasma levels up to 96 hours and were well tolerated in AGMs, with comparable efficacy in postoperative pain control. EXR offers a compliant and effective alternative to compounded SRB for analgesia in AGMs, supporting its use in laboratory settings and regulatory compliance with current guidelines.