Pharmacodynamics of intermittent and continuous infusion piperacillin/tazobactam and cefepime against extended-spectrum beta-lactamase-producing organisms.

The pharmacodynamics of piperacillin/tazobactam and cefepime were evaluated against extended-spectrum beta-lactamase (ESBL)-producing organisms. Ten thousand patients were simulated based on ESBL minimum inhibitory concentrations (MICs) from our laboratory (N=39) and on pharmacokinetic data from peer-reviewed literature. The desired proportion of the dosing interval that the concentration remains above the MIC (%T>MIC) for the intermittent bolus regimens was >/=40% for piperacillin/tazobactam and >/=60% for cefepime. The desired C(ss)/MIC ratio (where C(ss) is the concentration at steady state) was >/=2 for all continuous infusion (CI) regimens. MIC(50), MIC(90) and %S were, respectively, 64/4mug/mL, 1024/4mug/mL and 33% for piperacillin/tazobactam and 8mug/mL, 16mug/mL and 0% for cefepime. For piperacillin/tazobactam, 3.375g every 4h (q4h) achieved the highest probability of target attainment (43%), followed by 13.5g CI (31%), 3.375g q6h (27%), 4.5g q8h (17%) and 6.75g CI (10%). However, for cefepime, 4g CI had the highest probability of target attainment (77%), followed by 1g q8h (65%), 2g q12h (58%), 3g CI (46%) and 1g q12h (27%). Although the probabilities of target attainment for cefepime were higher than for piperacillin/tazobactam, neither agent achieved a high probability of target attainment and should not be used routinely for the treatment of ESBL infections.