The purpose of this study is to analyze the PK/PD of AvyCaz in critically ill patients in the Intensive Care Unit (12). This study will include medical and post-surgical patients who develop an infection where Avycaz can be utilized. Since these patients will have variable PK parameters, the investigators will also analyze (time-kill) these serum concentrations (ex vivo) against relevant clinical isolates (e.g. GNR with ESBL or KPC) from the ICU to determine microbiologic activity of Avycaz in critically ill patients with variable characteristics. Monte-Carlo simulations will also be conducted against clinical ICU isolates (JMI labs) to help determine appropriate dosing schedules based upon these PK parameters.

Inclusion Criteria:

• Adult (≥18y/o) patients with a medical or post-surgical infection such as skin/soft tissue infections, urinary infections, IA infections and pneumonia (including VAP)
• Patients requiring intensive care (critically ill patients) in the med/surg ICU (APACHE II score ≥ 15)
• Patients prescribed Avycaz for their infection will receive FDA recommended dosages and times of administration
• Written informed consent

Exclusion Criteria:

• Pregnant Patients, patients older than 90 y/o, those with CrCl < 30 mL/min, patients with a BMI > 45 Kg/m2, patients unable to provide serum samples, and those with the risk of imminent death during the study

1 week