Infections caused by gram-negative microorganisms resistant to carbapenems have been increasingly recorded in the past decade and lead to high mortality rates. In a number of in vitro studies, the synergistic effect of combination therapy, including polymyxin B, carbapenem and rifampicin, on these problematic pathogens has been demonstrated. At the same time, the clinical data currently available are only limited by the results of retrospective studies.

A cohort observational study was conducted in patients over 18 years of age who were prescribed combination therapy, including polymyxin B. The average age of the patients was 77 years. The majority (73%) of patients have recently received antimicrobial treatment, 67% of people have already been hospitalized and almost half (47%) lived in long-term care facilities. The most common infections were pneumonia and urinary tract infections caused by Acinetobacter baumannii (33%), Klebsiella pneumoniae (24%) and Pseudomonas aeruginosa(11%). The treatment regimens included the use of a combination of polymyxin B and carbapenem in 48% of the cases, and rifampicin was also used in 23% of the cases.

The clinical efficacy of the treatment was reached in 50% of the cases, reinfection was diagnosed in 25% of the patients. Treatment-related acute renal failure occurred in 14.4% of cases, but no hemodialysis was ever required in this regard. For all reasons, the death rate was 47%; the mortality rate after 6 months was 77%. There were no statistically significant differences between the regimens applied. Age (odds ratio 10.4 for 10 years, p = 0.04), severity of acute infectious disease (OS 2.2 for 1 point, p less than 0.001) and Charlson score (OS 1.12 for 1 point, p = 0.04) were predictors of nosocomial mortality. In the case where infection was caused by K. pneumoniae, the nosocomial survival rate was higher than that of other gram-negative microorganisms resistant to carbapenems (p = 0.03 ).

Infections caused by gram-negative microorganisms resistant to carbapenems occur more often in patients who have already received antibiotic therapy, and in people living in long-term care facilities or recently treated in a hospital. The mortality rate depends on the patient's age and the severity of the underlying acute infectious disease and the associated chronic pathology.