Pharmacokinetic studies on the concomitant administration of piperacillin and cefazolin, and piperacillin and cefoperazone in rabbits.

The pharmacokinetics of each drug on the concomitant administration of piperacillin (PIPC) and cefazolin (CEZ) or cefoperazone (CPZ) were studied in rabbits. When rabbits received the consecutive drip infusion administration of CEZ (0.71 mg/kg/minute) and PIPC (1.38 mg/kg/minute) and likewise of CPZ (0.72 mg/kg/minute) and PIPC (1.54 mg/kg/minute) for 1 hour, respectively, the serum half-lives of CEZ and CPZ were respectively prolonged about 1.8 and 1.6 times during drip infusion of PIPC than administered alone. However, when the sequence of administration were reversed, the serum levels of PIPC were not affected by the consecutive drip infusion administration of CEZ and CPZ. To study these findings in detail, the single intravenous dose of 20 mg/kg of CEZ and CPZ were administered under drip infusion of PIPC (2.65-2.93 mg/kg/minute). The serum half-lives of CEZ and CPZ were also prolonged about 5.4 and 1.9 times, respectively, whereas urinary excretion of CEZ, and urinary and biliary excretion of CPZ were reduced by PIPC. Moreover, when the single intravenous dose of 20 mg/kg of PIPC were administered under drip infusion administration of CEZ (0.96- 2.60 mg/kg/minute), the pharmacokinetics of PIPC was not affected by the presence of CEZ. However, under drip infusion administration of CPZ (2.60-2.70 mg/kg/minute), the PIPC serum half-life was prolonged about 1.4 times, and biliary excretion of PIPC was reduced but urinary excretion was not. From the results of renal clearance experiments, tubular secretion appeared to be the predominant mechanism of renal elimination for these three drugs. These results indicate that PIPC influences the pharmacokinetics of both drugs by the competitively inhibiting tubular secretion in CEZ, and tubular secretion and hepatic transport system in CPZ. Therefore, in this respect PIPC seems to have probenecid-like action.