What is the recommended treatment for a carbapenem‑resistant Escherichia coli infection?

Treatment of Carbapenem-Resistant E. coli

For carbapenem-resistant E. coli infections, ceftazidime-avibactam is the preferred first-line agent for KPC- and OXA-48-producing strains, while ceftazidime-avibactam combined with aztreonam should be used for metallo-β-lactamase (MBL)-producing strains. 1

Treatment Algorithm Based on Carbapenemase Type

Step 1: Identify the Carbapenemase Mechanism

The carbapenemase type must be determined before selecting therapy whenever possible. 1

• KPC-producing strains: Nearly 100% susceptible to ceftazidime-avibactam 1
• OXA-48-producing strains: Nearly 100% susceptible to ceftazidime-avibactam 1
• Metallo-β-lactamase producers (NDM, VIM, IMP): Require combination therapy with ceftazidime-avibactam plus aztreonam 1

Step 2: Select Appropriate Therapy

For KPC and OXA-48 Producers (Severe Infections)

Use ceftazidime-avibactam monotherapy or meropenem-vaborbactam as first-line agents. 2, 3

• Ceftazidime-avibactam reduces mortality by 182 fewer deaths per 1000 patients (RR 0.55,95% CI 0.42-0.72) compared to other antimicrobials 1
• Treatment failures reduced by 307 per 1000 patients (RR 0.49,95% CI 0.34-0.70) 1
• Acute renal injury reduced by 95 per 1000 patients (RR 0.55,95% CI 0.23-1.33) 1
• Do not use combination therapy when treating with ceftazidime-avibactam or meropenem-vaborbactam for susceptible strains 2

For Metallo-β-lactamase Producers (NDM, VIM, IMP)

Use ceftazidime-avibactam combined with aztreonam as the preferential regimen. 1

• Aztreonam is not hydrolyzed by metallo-β-lactamases and shows excellent in-vitro synergy with ceftazidime-avibactam 1
• This combination achieved 30-day mortality of 19.2% versus 44% with other active agents (P = 0.007) 1
• Hazard ratio for 30-day mortality: 0.37 (95% CI 0.13-0.74) 1
• Clinical treatment failure rate: HR 0.30 (95% CI 0.14-0.65) 1
• Consider adding polymyxin or fosfomycin for critically ill patients with NDM-producing strains 1

For Strains Resistant to All New β-lactam/β-lactamase Inhibitors

Use cefiderocol if susceptibility is confirmed, particularly for MBL-producing strains resistant to ceftazidime-avibactam. 2, 3

• Cefiderocol is conditionally recommended for severe infections due to CRE carrying metallo-β-lactamases and/or resistant to ceftazidime-avibactam and meropenem-vaborbactam 2
• For severe infections with only polymyxin, aminoglycoside, tigecycline, or fosfomycin susceptibility, use combination therapy with more than one active agent 2
• Aztreonam plus ceftazidime-avibactam combination is suggested for MBL-producing strains resistant to monotherapies 2

Step 3: Infection Site-Specific Considerations

Non-Severe Complicated Urinary Tract Infections

Use aminoglycosides (including plazomicin) for short-duration therapy or IV fosfomycin when active in vitro. 2

• Aminoglycosides are preferred over tigecycline for cUTI 2
• Avoid tigecycline for bloodstream infections and hospital-acquired/ventilator-associated pneumonia 2

Bloodstream Infections and Severe Infections

Prioritize ceftazidime-avibactam, meropenem-vaborbactam, or cefiderocol based on susceptibility and carbapenemase type. 2, 3

• For BSI without septic shock, consider step-down therapy once stabilized based on susceptibility patterns 2

Critical Pitfalls to Avoid

Avoid Polymyxins When Alternatives Exist

Colistin and polymyxin B should be avoided due to nephrotoxicity and lack of robust clinical efficacy data. 3, 4

• Use polymyxin-based combinations only when no other options are available 2
• Monitor renal function closely if polymyxins must be used 1

Do Not Use Tigecycline for BSI or Pneumonia

Tigecycline should not be used for bloodstream infections or hospital-acquired pneumonia due to poor outcomes. 2

• If absolutely necessary for pneumonia, use high-dose tigecycline regimens 2
• Tigecycline may be considered only for non-severe infections when other options are unavailable 2

Avoid Carbapenem-Based Combinations

Do not use carbapenem-based combination therapy for CRE infections unless meropenem MIC is ≤8 mg/L, where high-dose extended-infusion meropenem may be part of combination therapy. 2

Reserve New Agents Appropriately

New β-lactam/β-lactamase inhibitors should be reserved for carbapenem-resistant organisms and not used for carbapenem-susceptible strains due to antimicrobial stewardship considerations. 2

Quality of Evidence Considerations

The evidence supporting these recommendations is predominantly of very low to moderate quality, derived primarily from observational studies 1. However, the consistent mortality benefit observed with ceftazidime-avibactam across multiple studies (182 fewer deaths per 1000 patients) provides reasonable confidence in its use as first-line therapy for KPC- and OXA-48-producing strains 1. The combination of ceftazidime-avibactam with aztreonam for MBL producers shows the most dramatic mortality reduction (from 44% to 19.2%) despite very low-quality evidence 1.