Potential Benefit Seen with Combination Therapy for Carbapenem-Resistant Infections – New Study Offers Hope Against Superbugs
New Brunswick, NJ & Ann Arbor, MI – July 26, 2025 – A new study published today in Clinical Infectious Diseases suggests that combining colistin with meropenem may improve outcomes for patients battling severe infections caused by carbapenem-resistant bacteria, particularly in cases of pneumonia. While overall mortality rates weren’t significantly impacted across all infection types, teh research, led by Dr. Mariya Huralska of Rutgers Robert Wood Johnson Medical School and Dr. Jason M. Pogue of the University of Michigan College of Pharmacy, reveals a promising trend in bloodstream infections and a statistically significant reduction in clinical failure rates for pneumonia patients.
This research arrives at a critical juncture as antimicrobial resistance continues to escalate globally, posing a significant threat to public health. Carbapenem-resistant organisms – bacteria that have developed resistance to one of the most powerful classes of antibiotics – are increasingly common, leading to longer hospital stays, higher medical costs, and increased mortality. The Centers for Disease Control and Prevention (CDC) identifies these organisms as serious threats, classifying Acinetobacter baumannii as one of the most concerning.
Understanding the Challenge: Carbapenem Resistance & Synergy
The study focused on patients infected with three particularly problematic carbapenem-resistant bacteria: Acinetobacter baumannii (the most prevalent in the study, affecting 320 patients), carbapenem-resistant Enterobacterales (64 patients), and carbapenem-resistant Pseudomonas aeruginosa (41 patients). These bacteria are notorious for their ability to acquire resistance mechanisms, making infections challenging to treat.
The researchers investigated weather combining colistin (a polymyxin antibiotic) with meropenem – a strategy based on the potential for synergistic activity – would improve patient outcomes compared to using colistin alone (functional monotherapy). Synergism occurs when the combined effect of two drugs is greater then the sum of their individual effects. This is particularly relevant with A. baumannii,where synergy between colistin and meropenem is frequently observed.Key Findings & Nuances
The study,conducted across multiple sites (specific locations were not detailed in the provided text),enrolled a total of 425 patients. Here’s a breakdown of the key results:
Overall Mortality: mortality rates were comparable between the combination therapy group (38.4%) and the functional monotherapy group (41.4%). This suggests that for the entire cohort, the combination didn’t offer a statistically significant survival advantage.
Bloodstream Infections: A trend towards reduced mortality was observed in patients with bloodstream infections receiving the combination therapy (adjusted odds ratio [aOR] 0.42; P = .054). While not statistically significant at the conventional 0.05 threshold, the P-value is close, suggesting a potential benefit that warrants further investigation.
Pneumonia: significantly reduced clinical failure rates were seen in patients with pneumonia treated with the synergistic combination (62.6% vs. 71.8%; aOR, 0.54; P = .04). This means fewer patients in the combination group experienced treatment failure, defined as death within 7 days, needing rescue therapy, treatment discontinuation due to adverse events, persistent bacteremia, or worsening oxygenation.
A. baumannii Pneumonia: A similar, though non-significant, trend towards reduced clinical failure was observed specifically in patients with A.baumannii pneumonia (57.4% vs. 69.4%; aOR, 0.60; P = .06).
Microbiologic Cure: Microbiologic cure rates – the eradication of the bacteria from the body – were similar between the two groups, indicating that the combination therapy didn’t necessarily improve bacterial clearance.
Clinical Implications & Future Directions
The authors suggest that, given the frequent synergism between colistin and meropenem in A. baumannii infections, combination therapy with meropenem should be considered when treating severe A. baumannii infections with polymyxin-based regimens. However, they caution that the findings may not be directly applicable to polymyxin B, as colistin was used in the trial.
Study Limitations & Considerations
The researchers acknowledge several limitations:
Dominance of A. baumannii: Over 75% of the study pathogens were A.baumannii, limiting the statistical power to draw firm conclusions about the effectiveness of the combination therapy against carbapenem-resistant Enterobacterales and P. aeruginosa.
