DISPOSITION KINETICS AND BIOAVAILABILITY OF PIPERACILLIN AND CEPHAPIRIN IN MARES

The pharmacokinetics of piperacillin (430 mg/kg.b.wt.) and cephapirin (20 mg/kg.b.wt.) were investigated following a single intravenous and intramuscular injection in normal mares. The serum concentration-time curve following a single intravenous injection of both antibiotics obeyed a two-compartment open model. After intravenous dose, piperacillin and cephapirin were transferred from central to peripheral compartment (k(12)) with values 0.46 and 0.52 h(-1), while their passages from peripheral to central compartment (k(21)) were equal to 0.56 and 0.49 h(-1), respectively. The elimination half-lives {[}t(0.5)] following intravenous injection were 6.94 and 3.82 h for piperacillin and cephapirin, respectively. Piperacillin and cephapirin were cleared after intravenous injection by all clearance processes in the body (Cl-tot) at rates of 5.52 and 0.67 ml/min., respectively. The absorption half-lives {[}t(0.5(ab))] of piperacillin and cephapirin following a single intramuscular injection were 0.46 and 0.88 h., respectively. The calculated maximum {[}(C) over bar(max)] and minimum {[}(C) over bar(min)] serum concentrations to establish a proper multiple dosage regimen were 52.94, 4.50 mu g/ml (for piperacillin) and 10.18, 2.20 mu g/ml (for cephapirin), respectively. The mean systemic biovailabilities of piperacillin and cephapirin following a single intramuscular injection were 85.47\% and 67.89\%, respectively. The in-vitro protein binding percent was 19.23\% for piperacillin and 52.62\% for cephapirin.