Previous studies have identified Acinetobacter baumannii (AB), Pseudomonas aeruginosa (PA), and Klebsiella pneumoniae (KP) as the predominant pathogens responsible for ventilator-associated pneumonia (VAP). The challenge of drug resistance, especially against carbapenem is intensifying, with variations noted across different regions. Multidrug-resistant organisms associated VAP (MDR-VAP) are increasing in frequency and are associated with significant morbidity, mortality, therefore imposes a heavy burden on the healthcare system. Colistin methanesulfonate sodium (CMS) has shown effectiveness against gram-negative bacteria, including carbapenem-resistant organisms (CRO) such as carbapenem-resistant Acinetobacter baumannii (CRAB), carbapenem-resistant Pseudomonas aeruginosa (CRPA), and carbapenem-resistant Klebsiella pneumoniae (CRKP). This trial aims to evaluate the efficacy of a 3-day course of inhaled CMS in lowering the incidence of VAP among patients undergoing invasive mechanical ventilation for at least two days and at high risk of MDR-VAP.

Ventilator-Associated Pneumonia (VAP) is defined as pneumonia that develops 48-72 hours or more following the initiation of mechanical ventilation. It is a critical infection acquired in the Intensive Care Unit (ICU), significantly contributing to increased mortality rates, extended ICU stays, and elevated healthcare costs for patients on ventilators[1]. VAP is reported to affect 5-40% of patients receiving mechanical ventilation, with an average incidence of 20-25%. This proportion has been exacerbated in recent years by the COVID-19 pandemic[2-4]. A meta-analysis encompassing 195 studies found that the overall cumulative incidence of VAP in mainland China is 23.8% (95% CI 20.6-27.2%)[5].

Numerous risk factors, such as prolonged mechanical ventilation, advanced age, supine body position, prior antibiotic use, and various comorbidities, in addition to the endotracheal intubation itself, have been associated with the development of VAP[6, 7]. VAP results from the invasion of pulmonary parenchyma by pathogenic bacteria, which overwhelm the host's weakened defense capability. The primary sources of these bacteria include oropharyngeal colonization, secretions around the endotracheal tube cuff, and biofilm formation on the tracheal tube. The infectious process initiates at the time of intubation and progresses over several days. Reports indicate that the daily risk of VAP peaks between days 5 and 9 of incubation, underscoring the need for early preventive measures[8]. Despite decades of research highlighting interventions such as patient positioning adjustments, daily awakening and weaning protocols, oral decontamination, and systemic antibiotics to reduce VAP incidence, the burden remains unacceptably high.

Systemic antibiotics are commonly used for both treatment and prevention of VAP. However, the risk of resistant bacteria selection is a significant concern. A meta-analysis of six trials indicated that prophylactic antibiotics administered via nebulization effectively reduced VAP occurrence without increasing the risk of multidrug resistant (MDR) pathogen-related VAP[9]. Another Meta-Analysis consisting seven RCTs also confirmed that pro- phylactic antibiotics delivered via the respiratory tract reduced the risk of VAP, particularly for those treated with nebulized aminoglycosides[10]. Additionally, a short course of aerosolized ceftazidime significantly decreased VAP frequency in critically ill trauma patients without adversely affecting bacterial pathogen profiles and sensitivity patterns[11]. Recently, a study of 3-day course of inhaled amikacin was shown to effectively reduce the incidence of VAP[12, 13]. Stephan Ehrmann's team confirmed the possibility of inhaled amikacin to lessen the VAP burden during a 28-day follow-up period. This study provides us with excellent inspiration and suggests promising prospects for the use of nebulized antibiotics in preventing VAP. However, there are still more than 10% of patients who have amikacin resistance that can not be covered among all participants and the burden of MDR-VAP has becoming increasingly heavy with variations across different regions. Data from China Antimicrobial Surveillance Network (CHINET 2024) shows the resistance rates of Acinetobacter baumannii (AB), Klebsiella pneumoniae (KP), and Pseudomonas aeruginosa (PA) to amikacin are 49.5%, 15.5%, and 3.4%, respectively. In contrast, the resistance rates of carbapenem-resistant Acinetobacter baumannii (CRAB), carbapenem-resistant Klebsiella pneumoniae (CRKP), and carbapenem-resistant Pseudomonas aeruginosa (CRPA) to amikacin are as high as 77.4%, 67.1%, and 11.4%, respectively.

Given the effectiveness of CMS against gram-negative bacteria including carbapenem-resistant organisms (CRO), we are optimistic about the potential of nebulized CMS inhalation to prevent VAP. So we designed the study to evaluate the efficacy and safety of prophylactic CMS nebulization in preventing VAP among incubated patients at high risk of MDR-VAP. We hypothesize that administering a 3-day course of pre-emptive inhaled CMS after 2 days of ventilation will reduce the subsequent incidence of VAP.

Participants will be enrolled if they meet the following criteria:

1. Age ≥18 years;
2. Mechanical ventilation for more than two consecutive days (48 hours);
3. Patient has high-risk factors for multidrug-resistant bacterial infections, which meet any of the following criteria:

(1)History of antibiotic exposure within 30 days; (2)Hospitalization time>5 days (120 hours); (3)Septic shock; (4) ARDS; (5)Accept renal replacement therapy; (6)Previous colonization of multidrug-resistant bacteria; 4. Informed consent of the patient or a proxy was written.

Participants will be excluded in case of:

1. Suspected or confirmed VAP at the inclusion day;
2. Patient ventilated through an endotracheal tube for more than four consecutive days (96 hours);
3. Expected that endotracheal intubation will be removed within the next 24 hours;
4. Tracheostomy;
5. Allergy to CMS;
6. Patients has polymyxins medication history within 7 days or clinical indication for systemic CMS therapy at the inclusion day;
7. Chronic kidney failure with baseline glomerular filtration ≤30 mL/min or Stage 3 classification AKI (KDIGO) (excluding patients undergoing renal replacement therapy);
8. Expected survival time not exceeding 48 hours;
9. Pregnancy or breastfeeding period;
10. Patients previously included in this study or are using any inhaled antibiotics or are participating in other clinical studies within 30 days.

Study protocol and informed consent form will be shared with other researchers when start this trial.

Study protocol and ICF will be shared with other researchers when start this trial for five years.

Ever researchers can access our study protocol and ICF from the web of clinical trials.gov.