Predictors of Subcutaneous Injection Site Reactions to Sustained-Release Buprenorphine in Rhesus Macaques (Macaca mulatta)

Pharmacokinetic Profiles of a New Extended-release Buprenorphine Formulation in Cynomolgus Macaques (Macaca fascicularis)

The primary objective of this study was to evaluate the pharmacokinetic profile of a new extended-release formulation of buprenorphine (BupBaseER) at a dose that would produce pain management of the desired duration. A secondary objective was to compare the incidence of injection site reactions between the original extended-release formulation (BupHClER) and BupBaseER, which uses a different proprietary polymer-based vehicle than does the BupHClER formulation. Eighteen cynomolgus macaques (M. fascicularis) were divided into 2 groups. Each macaque in the first group (n = 6) received a single subcutaneous injection of 0.06 mg/kg BupBaseER (10 mg/mL) followed at least 2 wk later by a single subcutaneous injection of 0.12 mg/kg. Animals in group 2 (n = 12) received 2 injections of each of 3 compounds-the original polymer matrix vehicle used in BupHClER, the modified polymer matrix vehicle used in BupBaseER, and 0.9% saline-in designated areas of the dorsoscapular region. The 0.06- and 0.12-mg/kg doses both maintained therapeutic levels that were 3 times higher than the hypothesized analgesic threshold of 0.1 ng/mL. These doses maintained therapeutic level for approximately 44 and 103 h, respectively. Based on these data, buprenorphine concentration likely remains well above the therapeutic threshold beyond the 120 h span of this study. During the 30 d after administration, one macaque had a mild skin reaction to BupHClER. None of the animals in either group had skin reactions to BupBaseER at either dosage. These findings support the use of BupBaseER to provide pain management, promote animal welfare, decrease animal stress, and simplify the postoperative management of NHP in research and zoological settings.

Evaluation and comparison of pharmacokinetic profiles and safety of two extended-release buprenorphine formulations in common marmosets (Callithrix jacchus)

While sustained-release buprenorphine (BSR) is used as a long-lasting opioid analgesic in common marmosets (Callithrix jacchus), there are no published studies on pharmaceutical-grade extended-release buprenorphine options such as Ethiqa XR (EXR) for this species. However, BSR is a compounded product and has been reported to cause injection site reactions in multiple species, including marmosets. Additionally, now with the availability of EXR, a pharmaceutical-grade veterinary product, the use of BSR in laboratory animals is not compliant with the Guide for the Care and Use of Laboratory Animals (Guide) unless scientifically justified and approved by the IACUC. We compared pharmacokinetic and safety profiles of BSR (0.15 mg/kg) and EXR (0.1-0.2 mg/kg) administered subcutaneously to adult marmosets. Blood was collected by venipuncture of the saphenous vein at multiple time points (0.25-72 h) and analyzed by liquid chromatography-tandem mass spectrometry (LC-MS/MS). EXR between 0.1 and 0.2 mg/kg resulted in a dose-dependent increase in Cmax (1.43-2.51 ng/mL) and were not statistically different from BSR (1.82 ng/mL). Tmax, lambdaz, and t1/2 were not statistically different between formulations. Mean plasma buprenorphine concentrations for BSR and EXR exceeded the therapeutic threshold (0.1 ng/mL) within 0.25 h and lasted for > 72 h. Mild sedation, but neither respiratory depression nor ataxia, was observed for both formulations. BSR injection sites had significantly higher histopathological scores compared to EXR. Video recordings for monitoring drug-induced behavioral changes showed increased animal activity levels after BSR and EXR versus saline controls. Norbuprenorphine, a buprenorphine metabolite associated with respiratory depression, was detected in the plasma after BSR and EXR administration as well as by in vitro liver microsome assays. In conclusion, we recommend using EXR over BSR as a long-lasting buprenorphine analgesic in marmosets because EXR is a pharmaceutical-grade formulation that is compliant with FDA guidelines and the Guide as well as exhibits comparable PK and safety profiles as BSR.

Long-Acting Opioid Analgesics for Acute Pain: Pharmacokinetic Evidence Reviewed

Long-acting injectable (LAI) opioid formulations mitigate the harm profiles and management challenges associated with providing effective analgesia for animals. A single dose of a long-acting opioid analgesic can provide up to 72 h of clinically relevant pain management. Yet, few of these new drugs have been translated to products for veterinary clinics. Regulatory pathways allow accelerated drug approvals for generic and biosimilar drugs. These pathways depend on rigorous evidence for drug safety and pharmacokinetic evidence demonstrating bioequivalence between the new and the legacy drug. This report reviews the animal PK data associated with lipid and polymer-bound buprenorphine LAI formulations. Buprenorphine is a widely used veterinary opioid analgesic. Because of its safety profile and regulatory status, buprenorphine is more accessible than morphine, methadone, and fentanyl. This review of PK studies coupled with the well-established safety profile of buprenorphine suggests that the accelerated approval pathways may be available for this new family of LAI veterinary pharmaceuticals.