OBJECTIVE To describe concentration-over-time data for ampicillin and sulbactam in the digital and systemic circulations and synovial fluid (SYN) of cattle following a single injection of ampicillin-sulbactam as a regional IV perfusion (RIVP). ANIMALS 6 healthy adult nonlactating Jersey-crossbred cows. PROCEDURES The right hind limb of each cow was aseptically prepared. A tourniquet was applied around the midmetatarsal region, and 1.0 g of ampicillin with 0.5 g of sulbactam in a combined formulation was administered as an RIVP into the dorsal common digital vein (DCDV). Blood samples from the DCDV and jugular vein and SYN samples from the metatarsophalangeal joint of the prepared limb were collected immediately before and at predetermined times for 24 hours after RIVP. One blood sample was obtained from the abaxial proper plantar vein of the lateral digit of the prepared limb 0.25 hours after RIVP. Serum and SYN ampicillin and sulbactam concentrations were determined by high-performance liquid chromatography. RESULTS Mean ± SD maximum concentration of ampicillin in SYN and serum obtained from the abaxial proper plantar and jugular veins was 1,995 ± 1,011 μg/mL, 5,422 ± 1,953 μg/mL, and 2.5 ± 1.6 μg/mL, respectively. Corresponding serum and SYN concentrations of sulbactam were lower but followed the same pattern over time as those for ampicillin. Synovial fluid ampicillin concentration remained above 8 μg/mL for a mean time of 18.9 hours. CONCLUSIONS AND CLINICAL RELEVANCE Potentially therapeutic concentrations of ampicillin were achieved in regional serum and SYN samples; SYN concentrations remained at potentially therapeutic values for > 12 hours following RIVP of 1.5 g of ampicillin-sulbactam in the hind limb of healthy cows.
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