Treatment of Acinetobacter Baumannii MDRO Infections
For carbapenem-resistant Acinetobacter baumannii (CRAB) infections, colistin-based therapy, with or without carbapenems, is the recommended first-line treatment, with consideration of adjunctive inhaled colistin for pneumonia. 1
First-Line Treatment Options
Bloodstream Infections
- Colistin-carbapenem combination therapy is recommended for CRAB bloodstream infections 1
Pneumonia
- Colistin with adjunctive inhaled colistin is recommended 1
- Tigecycline monotherapy is NOT recommended for CRAB pneumonia 1
- Duration of treatment should be individualized, with approximately 14 days for severe infections such as VAP 1
Intra-abdominal Infections
- Polymyxin-based combination therapy is recommended 1
- Alternative: Tigecycline 100 mg IV loading dose then 50 mg IV q12h or eravacycline 1 mg/kg IV q12h 1
Urinary Tract Infections
- Aminoglycoside monotherapy (if susceptible) is an option 2
- Gentamicin 5-7 mg/kg/day IV once daily or amikacin 15 mg/kg/day IV once daily 2
Dosing Recommendations for Key Antibiotics
| Antibiotic | Dosing Regimen |
|---|---|
| Colistin | Loading dose 6-9 million IU, then 9 million IU/day in 2-3 doses |
| Polymyxin B | Loading dose 2-2.5 mg/kg, then 1.5-3 mg/kg/day in 2 doses |
| Meropenem | 2g every 8 hours (extended infusion recommended) |
| Sulbactam | 9-12 g/day in 3 daily doses (4-hour infusion recommended) |
| Tigecycline | Standard: 100 mg loading, then 50 mg q12h; High dose: 200 mg loading, then 100 mg q12h |
Combination Therapy Considerations
The evidence for combination therapy versus monotherapy is mixed:
- For severe infections or high bacterial loads, combination therapy may be beneficial 2
- The 2015 task force on management of A. baumannii infections found no convincing data to recommend combination therapy over monotherapy for directed therapy 1
- However, for clinical failures or isolates with MIC in the upper limit of susceptibility, combination therapy may be considered 1
Recommended Combinations:
- Colistin + carbapenem for bloodstream infections 1
- Sulbactam or polymyxin with a second agent (tigecycline, rifampicin, or fosfomycin) for clinical failures 1
NOT Recommended Combinations:
- Routine combination of colistin plus rifampin 1
- Combination of colistin and anti-Gram-positive agents (glycopeptides, telavancin, daptomycin) 1
Treatment Duration
- For ventilator-associated pneumonia: 7-14 days 2
- For severe infections such as VAP or bacteremia: 14 days, especially in those with severe sepsis or septic shock 1
- For less severe infections: shorter durations may be acceptable 1
Special Considerations
Monitoring:
Biofilm Formation:
- A. baumannii can form biofilms, which may require higher antibiotic concentrations 2
Risk Factors for Poor Outcomes:
- Prior colonization with A. baumannii
- Immunosuppression
- Previous antimicrobial therapy
- Multiple invasive procedures
- Mechanical ventilation 2
Heteroresistance:
- Consider this phenomenon when treating A. baumannii infections, as it may affect treatment outcomes 2
Caveats and Pitfalls
Inappropriate Empiric Therapy:
- Significantly increases mortality; ensure coverage for potential CRAB if risk factors present 2
Renal Toxicity:
- Monitor renal function closely when using polymyxins or aminoglycosides
Emergence of Resistance:
- Can develop during treatment, particularly with colistin and tigecycline monotherapy
Evidence Quality:
- Most recommendations for CRAB treatment are based on low or very low-quality evidence 2
- Few randomized controlled trials exist; treatment decisions are often based on observational studies
Remember that early appropriate antimicrobial therapy is crucial for improving outcomes in CRAB infections, and susceptibility testing should guide definitive therapy whenever possible.