What is the treatment for Acinetobacter baumannii infections?

Treatment of Acinetobacter baumannii Infections

For Acinetobacter baumannii infections, treatment should be based on antimicrobial susceptibility testing, with carbapenems (imipenem, meropenem, doripenem) as first-line therapy for susceptible isolates and polymyxins (colistin) or ampicillin-sulbactam for carbapenem-resistant strains. 1

First-Line Treatment Based on Susceptibility

Carbapenem-Susceptible A. baumannii

• Carbapenems (imipenem, meropenem, doripenem) are the drugs of choice for infections caused by susceptible strains 1, 2
• Imipenem is FDA-approved for A. baumannii infections in multiple sites including respiratory tract, skin and skin structure infections 2
• Ertapenem should never be used for A. baumannii infections due to intrinsic resistance 1

Carbapenem-Resistant A. baumannii (CRAB)

• For CRAB susceptible to sulbactam, high-dose ampicillin-sulbactam is preferred (9-12g/day total) 3
• For sulbactam-resistant CRAB, colistin (polymyxin E) is recommended if the isolate is susceptible in vitro 3
• Tigecycline may be considered for some CRAB infections, but resistance can develop during treatment 4

Specific Dosing Recommendations

• Ampicillin-sulbactam: 4-hour infusion of 3g sulbactam every 8 hours (9-12g/day total) for isolates with MIC ≤4 mg/L 1, 3
• Colistin: Loading dose of 9 million IU followed by maintenance doses of 4.5 million IU every 12 hours, with dose adjustment for renal function 1
• Imipenem: 500 mg every 6 hours or 1,000 mg every 8 hours for susceptible isolates; 1,000 mg every 6 hours for isolates with intermediate susceptibility 2

Combination Therapy Considerations

• Combination therapy may be considered for severe CRAB infections to improve outcomes and prevent resistance 3
• The combination of sulbactam or polymyxin with a second agent (tigecycline, rifampicin, or fosfomycin) may be considered for clinical failures or infections with MIC in the upper limit of susceptibility 5
• Avoid polymyxin-meropenem combination therapy for CRAB infections with high-level carbapenem resistance (MICs >16 mg/L) 1
• The routine combination of colistin plus rifampin is not recommended 5
• The combination of colistin and glycopeptides (e.g., vancomycin) is discouraged due to increased nephrotoxicity 5, 3

Treatment Duration

• Treatment duration should be individualized based on infection site and severity 5
• For severe infections such as ventilator-associated pneumonia (VAP) or bacteremia, maintain antimicrobial therapy for 2 weeks, especially in cases of severe sepsis or septic shock 5, 3
• For less severe infections, shorter durations may be acceptable 5
• For urinary tract infections, 7 days for uncomplicated cases and up to 14 days for complicated UTIs or those with systemic symptoms 6

Special Considerations for Specific Infections

Respiratory Infections

• For hospital-acquired/ventilator-associated pneumonia (HAP/VAP), consider nebulized antibiotics (colistin) as adjunctive therapy for MDR A. baumannii 5
• Avoid tigecycline monotherapy for pulmonary infections due to suboptimal outcomes 7

Urinary Tract Infections

• Remove or replace urinary catheters when possible, as catheterization is a risk factor for developing A. baumannii infections 6
• For uncomplicated UTIs with susceptible isolates, monotherapy is generally sufficient 6

Monitoring and Adverse Effects

• Monitor renal function in patients receiving colistin, as nephrotoxicity occurs in up to 33% of patients 1, 3
• Monitor for emergence of resistance during therapy, particularly with colistin and tigecycline 1, 4
• For patients receiving tigecycline, monitor prothrombin time if co-administered with warfarin 4

Common Pitfalls and Caveats

• A. baumannii has a high propensity for acquiring antibiotic resistance, making empirical treatment challenging 1, 8
• Misidentification of A. baumannii species can lead to inappropriate antibiotic selection 1
• Heteroresistance to various antibiotics has been reported in A. baumannii, further complicating treatment 1
• Infections caused by A. baumannii, especially those with inappropriate treatment, are associated with considerable mortality 9
• Risk factors for A. baumannii infection include severe underlying diseases, previous surgery, invasive procedures, treatment with broad-spectrum antibiotics, length of hospital stay, and admission to intensive care units 10, 11