 The PK parameters and MIC will be used to estimate pharmacodynamic parameters of exposure time above MIC. Using sparse sampling PK analysis, parameters clearance, Vd will be estimated for the following each of the cohorts. The plasma concentrations-time profiles of piperacillin-tazobactam will be presented in tabular and graphical form by subject, age cohort, and dosage level. The relationship between plasma concentrations andor PK parameters with demographic factors weight, gestational age, postnatal age, disease severity, toxicity and co-administered medications will be investigated. Analysis of potential relationships between drug and exposure in subjects and the resulting efficacy andor safety response will be conducted. 