Pharmacokinetic Evaluation of Topical Long-Acting Buprenorphine in New Zealand White Rabbits (Oryctolagus cuniculus).

Rabbits are commonly used as surgical models, thus requiring analgesics for painful procedures and optimal animal welfare. Buprenorphine, a partial µ opioid, is commercially available in various concentrations and sustained-release formulations and has historically been used as an analgesic in rabbits. A topical long-acting buprenorphine formulation (Zorbium, Bup-TP) has been approved for analgesic use in cats but has not yet been evaluated in rabbits. The present study evaluated the plasma concentrations and pharmacokinetic parameters of Bup-TP in New Zealand white rabbits (Oryctolagus cuniculus). Healthy adult male (n = 4) and female (n = 4) New Zealand white rabbits were used in a randomized crossover design and received a single high (7 mg/kg) and low (3 mg/kg) dose of Bup-TP. In this study, Bup-TP achieved a plasma blood concentration >0.25 ng/mL starting at 0.5 hours after dosing that was maintained up to 72 hours after dosing in adult New Zealand white rabbits. Compared with baseline, fecal and urinary output were reduced for an average of 3.5 days after dosing; food consumption was reduced for an average of 10 days after dosing. All resolved with time and supportive care. No lesions were grossly visible on any rabbit at site of application. Bup-TP may be an effective, long-lasting, and noninvasive method of providing analgesia in rabbits. Future study is recommended to optimize dosing and procedural analgesic efficacy.