Pharmacokinetics and Paw Withdraw Pressure in Guinea Pigs (Cavia porcellus) Treated with Transdermal Buprenorphine

The use of effective analgesia is a cornerstone of laboratory animal care, one that minimizes pain and distress while optimizing care and welfare. Guinea pigs are often used in biomedical research requiring appropriate pain management. In this study, we evaluated the pharmacokinetics and efficacy of transdermal buprenorphine (Zorbium), a commercial product labeled for use in cats. Guinea pigs (n = 12) received a transdermal dose of buprenorphine (2.7 mg per guinea pig), an average dose of 3.4 mg/kg, applied topically to the interscapular area. Plasma concentration, paw withdraw pressure (PWP) response, sedation scores, and body temperature were collected at 0, 0.25, 0.5, 1, 2, 4, 8, 12, 24, 48, 96, and 120 hours after application. Plasma concentrations peaked at 77.8 ng/mL at 1 hour and remained greater than the targeted 1.0 ng/mL for up to 120 hours, with a half-life of 46.7 hours. PWP peaked at 24 hours with 671.2 g of pressure, remained elevated through 48 hours at 364 g, and returned to baseline by 72 hours. Sedation scores (posture, ambulation, resistance to handling) were slightly elevated at 12 hours, body weight did not significantly change, and rectal temperatures remained normal at all time points. These results suggest that transdermal buprenorphine maintains a prolonged therapeutic plasma level and is an effective analgesic for up to 48 hours in guinea pigs, with minimal side effects. This formulation is an alternative to other buprenorphine formulations that would require less handling for guinea pigs.