Serum Concentrations of a Long-acting Cat Formulation of Transdermal Buprenorphine in C57BL/6 Mice

Long-acting analgesics such as extended-release buprenorphine are desirable in rodent medicine because they reduce needfor administration of additional medication and provide stable drug levels. We measured the serum concentrations of buprenorphineafter topical administration of a long-acting transdermal buprenorphine (LAT-bup) solution to female C57BL/6mice. We hypothesized that LAT-bup dosed topically at 40 mg/kg would achieve serum drug concentrations of greater than1 ng/mL, which is considered the therapeutic level for adequate analgesia in rodents. LAT-bup administered at 40 mg/kgresulted in serum drug concentrations above 1 ng/mL for all mice at time points 2, 4, 24, 48, 72, and 96 h ( n = 3/time point), asassessed by liquid chromatography-mass spectrometry. No adverse effects were noted when LAT-bup was dosed at either30 mg/kg or 40 mg/kg. We conclude that LAT-bup is easily administered to mice and achieves adequate blood levels for 96 h.Further studies evaluating analgesic efficacy are indicated.