This is prospective study to assess the pharmacodynamics (t>MIC) of 4.5 g every 6 h of piperacillin/tazobactam in patients with early phase of severe sepsis/septic shock following administration by a 30 min infusion.

Clinical and laboratory data such as age, sex, body weight, electrolyte, vital signs, APACHAE II score, BUN, Cr and fluid balance will be collected.

Fifty patients will be enrolled in this study. Piperacillin pharmacokinetic study will be carried out during the piperacillin/tazobactam therapy.

Each patient received 4.5 g every 6 h of piperacillin/tazobactam within 24 h of severe sepsis or septic shock, blood samples (approximately 3 ml) will be obtained by direct venipuncture at the following time: 0, 0-0.5, 0.5-2, 2-4 and 4-6 h after piperacillin/tazobactam therapy.

Concentration of piperacillin in plasma will be simulated in Monte Carlo technique to get PK/PD index and reported to % PTA and % CFR.

Inclusion Criteria:

• sepsis patient (defined by 2011 SCCM/ESICM/ACCP/ATS/SIS International sepsis definition conference)

• severe sepsis or septic sock was defined by

  • Severe sepsis (sepsis with organ dysfunction)
  • Septic shock (sepsis with systolic arterial pressure<90 mmHg, mean arterial pressure<60 mmHg or decrease systolic blood pressure> 40 mmHg from base line)

Exclusion Criteria:

• Patients who are pregnant.
• Patients who have documented hypersensitivity to beta-lactam
• Patients who are dialysis
• Patients who are severe sepsis or septic shock more than 24 hour