Goal of study:

To assess the tissular and plasma kinetics of ertapenem;

To determine the optimal dosages in the patients according to norepinephrine administration:

• to assess muscular diffusion of free form of ertapenem after administration to mechanically ventilated patients requiring such a treatment. The patients are included in the groups "with norepinephrine" or "without norepinephrine" according to their hemodynamic status.
• to assess the plasma pharmacokinetics of ertapenem in mechanically ventilated patients treated or not by norepinephrine.

Open-label, prospective study performed in a single ICU (16 beds) of a tertiary hospital (700 beds).

Inclusion Criteria:

• 18 years and more
• negative pregnancy test
• HIV/HBV, HCV negative tests
• Mechanical ventilation with pneumonia or intraabdominal infection requiring ertapenem

Exclusion Criteria:

• refractory septic shock requiring use of additional catecholamines
• patients with positives tests for HIV, HBV, HCV
• pregnant females
• allergic insufficiency
• hemodiafiltration
• contraindication to microdialysis catheter set-up
• severe arteritis of lower extremities
• treatment with vasodilatators
• prior history of aorto-iliac shunt
• involvement in a clinical trial in the last three months
• exclusion from national records
• non affiliated to "securité sociale"