Colistin monotherapy versus colistin-based combination therapy in the treatment of extensive drug-resistant Acinetobacter baumannii infections: A retrospective cohort study

Introduction: Acinetobacter baumannii is a Gram-negative Coccobacillus and is a frequent cause of hospital-acquired infections. Because some strains of A. baumannii are resistant to many antibiotics (i.e., extensively drug-resistant A. baumannii, or XDRAB), selecting antibiotics to treat infected patients is challenging. Clinical outcomes in critically ill patients with XDRAB infections are poor. In this study, we evaluated the clinical effectiveness of colistin as monotherapy and in combination with other antibiotics. Patients and Methods: A retrospective cohort study was performed on 94 critically ill patients (age ≥18 years) to assess the clinical effectiveness of treating XDRAB infections with colistin, either in monotherapy or combination with tigecycline, meropenem, or both. Clinical and microbiological data were obtained from patient records. We included patients suffering from XDRAB ventilation-associated pneumonia (VAP), or ventilator-associated tracheobronchitis (VAT), or VAT with bacteremia. Results: The mean age of the patients was 53.3 years (±23.7 years), and the mean Acute Physiology and Chronic Health Evaluation II score was 22.7 (standard deviation = 7.1). VAP and VAT with bacteremia were found in 84% and 16% of patients, respectively. Half (51%) of patients achieved microbiological clearance. The median Intensive Care Unit (ICU) stay was 29 days (interquartile range [IQR]: 17, 55) and the median mechanical ventilation (MV) duration was 21 days (IQR: 12, 42). MV duration and ICU length of stay were lower in the group of patients treated with colistin and meropenem than in those treated with colistin alone. Mortality was significantly lower in patients who received (colistin and tigecycline 30%) than in those who were treated with monotherapy (75%) with an odd ratio 0.03 (95% confidence interval: 0.00, 0.32; P < 0.01). Conclusions: Colistin-based combination treatment regimens mainly with tigecycline or with tigecycline and meropenem were associated with better treatment outcomes of XDRAB-induced VAP and VAT with bacteremia than colistin monotherapy.