Optimizing Dosing Regimen of Piperacillin/Tazobactam for Nosocomial Pneumonia

Inclusion Criteria: 1. Male or female, aged 18 to 70 years old. 2. Inpatients with nosocomial pneumonia or bacteremia. i. Diagnosis of nosocomial pneumonia 1. Chest radiographic infiltrate that is new or progressive. 2. At least two or more of the following clinical findings suggesting infection. * New onset of fever, oral temperature T\>38.3℃ or T\<36℃ * Purulent sputum * WBC \> 12×10\^9/L or \<4×10\^9/L, or band form \>10% * PaO2/FIO2\<240mmHg ii. Diagnosis of bacteremia: Positive blood culture and the isolated bacterial strain are considered to be infection cause. 3. Patients are infected by piperacillin-tazobactam susceptible pathogen with MIC=4, 8 or 16mg/L. Exclusion Criteria: 1. The patients who received systematic antibacterial treatment more than 48 hours before enrollment and have clinical response. 2. Severe pyemia with hypotension or/and evidences of failure of organic function (shock: systolic pressure \< 90mmHg or diastolic pressure \< 60mmHg, requiring more than 4 hours of administration of vasopressor(s)；renal impairment: urine volume \< 20 ml∕h or \< 80 ml∕4h after excluded any other potentials, acute renal failure need dialysis, CLcr\<40 mL/min). 3. Documented infection caused by pathogens beyond the antibacterial spectrum of piperacillin/tazobactam. 4. Previously diagnosed condition which tend to mimic or complicate the course and evaluation of the infectious process, e.g. bronchial obstruction, obstructive pneumonia, activate pulmonary malignancy, pulmonary abscess, empyema and active tuberculosis, which might interfere the course of the infectious disease and evaluation of the disease. 5. History of allergy to penicillins. 6. Pregnancy or breast-feeding women. 7. Any conditions investigator considered might increase the risk of patients or interfere study results.