CRAB infections in ICUs are on the rise, leading to higher morbidity, mortality, and healthcare costs due to resistance to most antibiotics, including carbapenems. The main resistance mechanisms include carbapenemases, efflux pumps, and changes in the bacterial cell wall.

Current treatments include polymyxins (Colistin, Polymyxin B), which are effective but can lead to resistance, aminoglycosides (Amikacin, Gentamicin), which are limited by resistance, and tetracyclines (Tigecycline, Eravacycline), which are effective against CRAB. Fosfomycin is effective in combination treatments, and combination therapy (e.g., colistin with sulbactam, fosfomycin, or eravacycline) can enhance outcomes.

Previous research shows promise for combination therapies, improving treatment efficacy and reducing mortality. New regimens are being studied to find optimal combinations. Individualized dosing is crucial, considering patient-specific factors like age, weight, and renal function. Adjustments depend on the infection site and comorbidities.

Strict infection control and antimicrobial stewardship programs (ASPs) are essential. ASPs focus on optimizing antibiotic use and reducing resistance through education and surveillance. Future directions include continued research for new drugs or combinations and strategies to overcome resistance and improve treatment efficacy.

Study goals include achieving negative samples after 10 days of therapy, 30-day survival, discharge rates, reduced SOFA scores, and improved clinical and radiological findings. A randomized study will compare colistin combined with fosfomycin, ampicillin/sulbactam, and eravacycline.

In summary, treating CRAB infections is complex, requiring combination therapy, individualized dosing, and strict infection control measures.

The primary goal will be to negativize positive samples (surveillance or diagnostic) after 10 days of therapy. In addition to the control samples with the same name, samples will be taken on the 4th, 7th, and 10th day after starting treatment.

The secondary objectives will include 30-day survival, discharge from the ICU, discharge from the hospital, reduction in SOFA score, rate of reinfection, and frequency of complications (deterioration of renal function). Reduction of CRP, PCT, and leukocytes, improvement of the clinical picture, improvement of radiological findings (such as X-ray of the lungs), and reduction of elevated body temperature will also be included.

Patients who require treatment in the ICU with a positive sample (surveillance or diagnostic) for A. baumannii, with clinical signs of infection (temperature >38.5, CPR >50, L >10000) (in which no infection can be explained by another cause) will be included.

Three groups will be formed:

1. colistin + fosfomycin
2. colistin + ampicilin/sulbactam
3. colistin + eravacyclin

The outcomes will include a negative sample, length of stay in the ICU, length of stay in the hospital, and reduction of SOFA score.

The hypothesis will be that the combination of fosfomycin with colistin and eravacyclin with colistin will lead to faster negative samples than the combination of ampicillin/sulbactam with colistin in intensive care unit patients diagnosed with carbapenem-resistant A. baumannii.

After obtaining approval from the ethics committee of KBC Zagreb, this study will be conducted at the UHC Zagreb, Department of Anesthesiology and ICU. Patients will be randomly divided according to a predetermined randomization table.

Upon arrival of a positive microbiological finding on A. baumannii, the Fosfomycin group will receive fosfomycin 8 g every 8 h, together with a colistin bolus of 6 million IJ, followed by 3 million IJ every 8 h. After the first day, the dose will be adjusted according to kidney and liver function. Therapy will be administered for 10 days.

Upon arrival of a positive microbiological finding on A. baumannii, the Ampicilin/sulbactam group will receive a bolus dose of ampicillin/sulbactam 2 g + 1 g and a continuous infusion of 8 g + 4 g over 24 h together (maximum daily dose 12 g/day) with a colistin bolus of 6 million IJ, followed by 3 million IJ every 8 h. After the first day, the dose will be adjusted according to kidney and liver function. Therapy will be performed for 10 days.

Upon arrival of a positive microbiological finding for A. baumannii, the Eravacyclin group will receive eravacycline at a dose of 1 mg/kg every 12 h for 60 min together with a colistin bolus of 6 million IU, and then 3 million IU every 8 h. After the first day, the dose will be adjusted according to kidney and liver function. Therapy will be administered for 10 days.

After the first positive microbiological finding for A. baumannii, the test will be repeated on the 4th, 7th, and 10th days from the start of therapy. The Charlson Comorbidity Index will be calculated for each patient upon inclusion in the study. The SOFA score will be calculated daily for each patient over 10 days.

Patient data from a hospital information system will be used in this study. Demographic data, comorbidities, habits (alcohol and cigarettes), Charlson comorbidity index, SOFA score, allergies, and the type of positive sample will be recorded. The Charlson Comorbidity Index will be calculated for each patient upon inclusion in the study. The SOFA score will be calculated daily for each patient over 10 days. Patients will be included in the study after the arrival of a microbiological test positive for A. baumannii. A routine antimicrobial susceptibility test will be performed when the microbiological findings are positive for A. baumannii. The sensitivity of all A. baumannii strains included in the study, regardless of the group to which they belonged (fosfomycin, ampicilin/sulbactam, and eravacyclin), will be determined during the microbiological analysis of all A. baumannii strains included in the study. After the first positive microbiological finding for A. baumannii, the test will be repeated on the 3th, 7th, and 10th days from the start of therapy. For each patient included in the study, inflammatory parameters (leukocytes, CRP, procalcitonin) and the number of days and discharge from the ICU and hospital as well as 30-day mortality and cause of death, complications (AKI and ALF), and reinfection will be monitored.

For a test power of 80% and the use of an independent t-test for the primary objective and a chi-square test for the secondary objective with a statistical significance of 0.05, it will be necessary to include 108 patients, divided into three groups, with 36 subjects per group. The test for power calculation will be conducted using G Power Version 3.1.9.6. The results will be processed using IBM SPSS Statistics v27.

Inclusion Criteria:

• Surgical patients (abdominal, vascular, and polytraumatized patients)
• Older than 18 years
• Require postoperative treatment in the ICU
• A positive sample (surveillance or diagnostic) for A. baumannii with signs of systemic infection

Infection will be defined as a diagnostic microbiologically positive sample for A. baumannii and a surveillance microbiologically positive sample for A. baumannii with signs of systemic infection (elevated CRP, leukocytes, and body temperature).

Colonization will be defined as a positive surveillance microbiological sample for A. baumannii in the absence of signs of systemic infection (normal CRP, leukocytes, and body temperature).

Exclusion Criteria:

• Allergy to the study medications
• Positive surveillance swabs for A. baumannii without signs of systemic infection
• Positive findings (surveillance or diagnostic) for carbapenem-sensitive A. baumannii
• Refusal to participate in the research