The pharmacokinetics of piperacillin/tazobactam will be evaluated in twenty septic patients with renal failure undergoing continuous veno-venous hemodiafiltration.

The pharmacokinetics of piperacillin/tazobactam will be evaluated in twenty septic patients with renal failure undergoing continuous veno-venous hemodiafiltration. This is a prospective study.

Continuous replacement therapy has a continuous effect on drug elimination which could compromise effective antibiotic treatment.

Patients will receive a standard course of pip/tazo 4g intravenously 8 hourly administrated immediately when CVVHDF will be started.

Blood samples will be collected at 30mn, 2h, 4h, 6h, 8h, 16h, 24h for the first and the second day.

We will measure plasma piperacillin/tazobactam concentration and compare them to MICs for the whole dosing interval.

Inclusion Criteria:

• 18 years of age and older .
• Females of childbearing potential must have a negative pregnancy test at screening.
• Subjects whose life expectancy is estimated over 7 days.
• Anuric patients requiring continuous venovenous hemodiafiltration
• Septic patients,severe sepsis or septic shock
• Written informed consent should be given either by the patient or a member of his family

Exclusion Criteria:

• Subjects with a history of true allergy or adverse drug reactions
• Pathogens whose antibiotic susceptibility is not proved.
• Patients having impaired hepatic function
• Contraindication of anticoagulation by heparin
• Residual renal function
• Participation in a clinical trial
• Interruption of treatment by piper/tazo or hemodiafiltration during the study.
• Patients with psychiatric disorder or serious medical condition which in the opinion of the investigator may lead to complexity in patient management.