Experimental studies of biliary excretion of piperacillin

The nonrecirculating isolated perfused rat liver was used to study biliary antibiotic excretion by the liver in a steady-state, controlled environment in which bile flow, bile salt output, and antibiotic delivery were maintained under constant conditions. The effects of piperacillin, ampicillin, and gentamicin on bile flow and bile salt output were analyzed; none altered bile salt output, and only high concentrations of piperacillin (100 micrograms/mL) increased bile flow. The ratio of antibiotic concentration in bile and perfusate depended on the type of antibiotic and perfusate concentration. Piperacillin infusions at perfusate concentrations of 50 or 100 micrograms/mL (in the presence of 60 microM taurocholate) yielded bile to perfusate ratios of 112 +/- 10 versus 49 +/- 3, respectively. Using similar perfusate, the concentration ratios for ampicillin (20 micrograms/mL) and gentamicin (10 micrograms/mL) were only 3.4 +/- 0.5 and 0.5 +/- 0.1, respectively. By altering the perfusate to contain either 60 microM or 240 microM taurocholate, we found variance in bile salt output from 27 +/- 1 to 115 +/- 2 mumol/h, yet this alteration had little effect on the output of ampicillin (perfusate concentration of 20 micrograms/mL), 73 +/- 7 versus 74 +/- 12 micrograms/h, or piperacillin (perfusate concentration 100 micrograms/mL), 10 +/- 1 versus 11 +/- 2 mg/h. Thus, it appears ampicillin and piperacillin are excreted into bile at high concentrations by bile salt-independent pathways. Partial biliary obstruction (6 cm H2O) results in significant decreases in bile volume. Infusion of 50 micrograms/mL of piperacillin resulted in increased biliary flow that approached nonobstructed values. Obstruction resulted in significant decreases in bile piperacillin concentration. Whether the choleretic effect of high concentrations of piperacillin has any clinical significance in nonobstructed or obstructed conditions remains to be established.