What are the recommended antibiotics for treating Acinetobacter (a type of bacteria) infections?

Antibiotic Treatment for Acinetobacter Infections

For carbapenem-susceptible Acinetobacter infections, use a carbapenem (imipenem, meropenem, or doripenem) as first-line therapy; for carbapenem-resistant strains, use high-dose ampicillin-sulbactam if the MIC is ≤4 mg/L, or intravenous polymyxins (colistin) if resistant to sulbactam. 1, 2

Initial Assessment and Susceptibility Testing

• Obtain cultures and antimicrobial susceptibility testing immediately before initiating antibiotics to guide definitive therapy, as treatment selection depends entirely on resistance patterns 1, 2
• Consider empirical Acinetobacter coverage in patients with prior colonization, active outbreak exposure, prolonged ICU stay with invasive procedures, recent carbapenem or third-generation cephalosporin use, or mechanical ventilation 2

Treatment Algorithm Based on Susceptibility

For Carbapenem-Susceptible Acinetobacter

• Use carbapenems (imipenem, meropenem, or doripenem) as the drugs of choice for all infection types including pneumonia, bacteremia, and skin/soft tissue infections 1, 2, 3
• Ertapenem should never be used for Acinetobacter infections as it lacks activity against this pathogen 1, 4
• Alternative option: Ampicillin-sulbactam if the isolate is susceptible (MIC ≤4 mg/L), particularly for hospital-acquired/ventilator-associated pneumonia 1

For Carbapenem-Resistant Acinetobacter (CRAB)

First-Line Options:

• Ampicillin-sulbactam: 9-12 g/day IV in 3-4 divided doses (administered as 4-hour infusions of 3g sulbactam every 8 hours) if sulbactam-susceptible with MIC ≤4 mg/L 1, 5
• Intravenous polymyxins (colistin or polymyxin B) if resistant to sulbactam: Loading dose of 5 mg colistin base activity (CBA)/kg IV, then maintenance of 2.5 mg CBA × (1.5 × CrCl + 30) IV every 12 hours 1

Alternative Options:

• Colistin plus tigecycline (100 mg IV loading, then 50 mg IV every 12 hours) for bloodstream infections or pneumonia, but never use tigecycline as monotherapy due to suboptimal serum concentrations 1, 4
• Sulbactam 6-9 g/day IV in 3-4 divided doses as monotherapy for non-severe infections 1

Combination Therapy Considerations

• Use combination therapy with two in vitro active agents for severe CRAB infections, including septic shock, high mortality risk (>25%), ventilator-associated pneumonia, or bacteremia with severe sepsis 1, 5
• For CRAB with meropenem MIC <8 mg/L, consider adding high-dose extended-infusion carbapenem (meropenem 2g IV every 8 hours infused over >3 hours or imipenem 500 mg IV every 6 hours) to colistin 1, 4
• Avoid polymyxin-rifampin combination as it lacks proven benefit and increases adverse effects without improving clinical outcomes 1, 4
• Avoid colistin plus glycopeptides (vancomycin) due to significantly increased nephrotoxicity without added benefit 4, 5

Special Considerations by Infection Site

Pneumonia/Ventilator-Associated Pneumonia (VAP):

• Add adjunctive inhaled colistin (1.25-15 million IU/day in 2-3 divided doses) to intravenous therapy for CRAB pneumonia 1
• Colistin for inhalation must be administered promptly after mixing with sterile water per FDA safety recommendations 1
• Strongly recommend against tigecycline monotherapy for pneumonia due to poor lung penetration 1

Bacteremia:

• Maintain therapy for 2 weeks minimum for bacteremia, especially with severe sepsis or septic shock 4, 5
• Never use tigecycline as monotherapy for bacteremia due to suboptimal serum concentrations and higher treatment failure rates 4

Treatment Duration

• 7 days for hospital-acquired and ventilator-associated pneumonia in patients showing clinical improvement 1
• 10-14 days for bloodstream infections without complications 1
• At least 2 weeks for severe infections including VAP or bacteremia with severe sepsis/septic shock 2, 4, 5

Critical Pitfalls to Avoid

• Never use ertapenem for Acinetobacter—it has no activity against this pathogen despite being a carbapenem 1, 4
• Never use tigecycline as monotherapy for pneumonia or bacteremia due to inadequate drug concentrations at these sites 1, 4
• Avoid carbapenem monotherapy for severe infections in areas with high CRAB prevalence (>25% resistance rates) 4
• Do not use adjunctive rifampin with colistin as this combination shows no clinical benefit and increases toxicity 1
• Monitor renal function closely in patients receiving colistin, as nephrotoxicity occurs in up to 33% of patients 2, 5
• Be aware that heteroresistance to colistin occurs in 18.7-100% of isolates in some series, potentially leading to rapid resistance development during therapy 2