The purpose of this study is to measure the change in plasma concentrations of antibiotics used during passage through the CRRT filter and hemadsorption cartridge in patients with septic shock and renal failure requiring CRRT. All patients aged \> 18 years, admitted to the ICU, diagnosed with septic shock and renal failure requiring CRRT, receiving antibiotic therapy with at least one of the following drugs: meropenem, linezolid, and daptomycin, who provided informed consent, are included in the study. Patients not admitted to the ICU, patients with renal failure not requiring CRRT, patients aged \< 18 years, or those who did not provide informed consent are excluded. The enrollment period will last 12 months and will run from September 2024 to September 2025. The expected number of patients enrolled is twenty. To proceed with the study, after starting antibiotic therapy, a 4 ml dose of blood will be drawn (Vacuette tube ref. 454092) before the cartridge, immediately after, and after the dialysis filter. This measurement will be repeated after 4, 8, and 12 hours, which represents the maximum usage time of the cartridge. After 12 hours, the cartridge becomes saturated and loses its adsorption capacity. The CRRT filter, however, remains in place for at least 72 hours before being replaced. Treatment is maintained until clinically necessary. For patients in intensive care, several blood samples are required throughout the day, both with a blood sample sent to the biochemistry laboratory every 6-8 hours to check clinical conditions, and with an arterial blood sample (blood gas) to check respiratory and metabolic status in patients on mechanical ventilation. Furthermore, in patients undergoing CRRT, electrolyte balance must be monitored every 4 hours. Therefore, the blood sample for the study inevitably coincides with one of the routine blood samples. The test tube, labeled with a unique code, will be sent to the central laboratory, which will centrifuge the blood and extract the plasma. This aliquot will then be stored at -80°C in a dedicated space and sent to the designated laboratory upon analysis. Determination of the plasma dosage of the antibiotic in use is commonly performed on patients admitted to the Intensive Care Unit, where clinically necessary. Participation in the study does not change current clinical practices.