The goal of this prospective cohort study is to characterize meropenem exposure in critically ill adult patients receiving empiric antibiotic treatment in the intensive care unit (ICU). Empiric treatment refers to the administration of antibiotics before the causative microorganism and its antimicrobial susceptibility profile are known. In clinical practice, meropenem is commonly administered using different dosing strategies, including 1 g or 2 g doses given as either a 30-minute or a 3-hour infusion. The minimum inhibitory concentration (MIC) is the lowest concentration of an antibiotic required to inhibit bacterial growth and is used as a reference value to evaluate antibiotic exposure. The main questions it aims to answer are:

Do meropenem plasma concentrations differ between patients receiving 1 g and those receiving 2 g, administered as either a 30-minute or a 3-hour infusion during the first 48 hours of empirical treatment in critically ill patients? Does the duration of time above the theoretical MIC of 2 mg/L differ between patients receiving meropenem 1 g and those receiving 2 g, administered as either a 30-minute or a 3-hour infusion during the first 48 hours of empirical treatment in critically ill patients?

Researchers will compare different meropenem dosing regimens (1 g versus 2 g administered as a 30-minute or a 3-hour infusion) to determine which strategy provides a longer duration of plasma concentrations above the theoretical MIC of 2 mg/L.

Participants will:

Receive meropenem as part of their standard clinical care. Have blood samples collected during the first 48 hours of treatment to measure meropenem plasma concentrations.

Have pharmacokinetic/pharmacodynamic parameters evaluated, including the percentage of time that meropenem concentrations remain above the theoretical target MIC.

An exploratory objective of the study is to describe 28-day mortality and intensive care unit length of stay according to meropenem dose group.

Inclusion Criteria:

• Adults ≥18 years of age.
• Hospitalization in the Intensive Care Unit (ICU), Intermediate Care Unit (ICU step-down/IMCU), or Coronary Care Unit (CCU).
• Receipt of empiric meropenem therapy for at least 24 hours, regardless of the site of infection.
• Written informed consent provided by the patient or their legally authorized representative prior to study participation.

Exclusion Criteria:

• History of severe adverse reactions to meropenem.
• Availability of microbiological identification results prior to blood sampling for meropenem concentration measurement.