What is the recommended therapy for infections caused by OXA-48-producing carbapenem-resistant Enterobacterales (CRE)?

Treatment of OXA-48-Producing CRE

For severe infections caused by OXA-48-producing carbapenem-resistant Enterobacterales, ceftazidime-avibactam is the preferred first-line therapy if the organism is susceptible in vitro. 1, 2

Severe Infections (Bloodstream Infections, Pneumonia, Septic Shock)

First-Line Therapy

• Ceftazidime-avibactam monotherapy is the treatment of choice for OXA-48 producers 1, 3
  • Nearly 100% of OXA-48-producing CRE are susceptible to ceftazidime-avibactam 2
  • Clinical studies demonstrate reduced mortality and treatment failure compared to older agents 2, 4
  • Combination therapy is NOT recommended when using ceftazidime-avibactam for susceptible isolates 1

Alternative Options (if ceftazidime-avibactam unavailable or resistant)

• Meropenem-vaborbactam if active in vitro 1
• Cefiderocol may be considered if susceptibility confirmed, though this is typically reserved for metallo-β-lactamase producers or extensively resistant organisms 1, 5

Important Caveat for OXA-48

OXA-48 producers often show low-level carbapenem resistance in vitro (meropenem MIC ≤8 mg/L), which can lead to false susceptibility reports. However, clinical outcomes with carbapenems alone are poor. Do not rely on carbapenem monotherapy even if the isolate appears susceptible 3, 6. The guideline explicitly recommends avoiding carbapenem-based combination therapy for CRE unless meropenem MIC is ≤8 mg/L, and even then, high-dose extended-infusion meropenem should only be considered as part of combination therapy when newer agents are unavailable 1.

Non-Severe Infections (Uncomplicated UTI, Low-Risk Infections)

For patients without septic shock or severe sepsis:

• Use older antibiotics based on individual susceptibility testing 1
• For complicated UTI: aminoglycosides (if active in vitro) or IV fosfomycin 1
• Consider fluoroquinolones, trimethoprim-sulfamethoxazole, or other agents if susceptible 1
• Avoid using new β-lactam/β-lactamase inhibitor combinations for non-severe infections due to antimicrobial stewardship considerations 1

Key Clinical Considerations

Monotherapy vs. Combination

• Monotherapy with ceftazidime-avibactam is sufficient for OXA-48 producers when susceptible 1, 7
• A large study (N=211) showed no benefit of combination therapy with ceftazidime-avibactam for OXA-48 infections (clinical cure 78%, 30-day mortality 21%) 7
• Combination therapy is only suggested when treating organisms resistant to all monotherapy options 1

Agents to Avoid

• Tigecycline should NOT be used for bloodstream infections or pneumonia 1
• Polymyxins (colistin, polymyxin B) should be avoided when newer agents are available due to toxicity and inferior outcomes 5, 3
• If polymyxins must be used, always use combination therapy, never monotherapy 2

Practical Pitfalls

1. Detection challenges: OXA-48 variants (especially OXA-244, OXA-484) are "difficult to detect" and may be underreported 8. Request carbapenemase genotyping when available
2. Susceptibility testing variability: Different methods (disk diffusion, ETEST, VITEK 2) show significant variability for OXA-48 producers 9. Ertapenem is the most reliable carbapenem for detecting resistance across all methods
3. Age matters: Patients <70 years have significantly better outcomes (OR 4.79) 4
4. Cost-effectiveness: Despite high cost, ceftazidime-avibactam is cost-effective for CRE bacteremia and pneumonia 2

Emerging Therapies

Newer β-lactamase inhibitors showing promise against OXA-48 include xeruborbactam, durlobactam, taniborbactam, zidebactam, and nacubactam 6, though these are not yet widely available for clinical use.