What is the recommended treatment for Acinetobacter lower respiratory tract infection (LRTI)?

Treatment of Acinetobacter Lower Respiratory Tract Infection

For carbapenem-susceptible Acinetobacter LRTI, use imipenem 0.5-1g IV every 6 hours or meropenem 2g IV every 8 hours (extended infusion preferred); for carbapenem-resistant strains, use IV polymyxin (colistin) combined with adjunctive inhaled colistin. 1, 2

Immediate Diagnostic Steps

• Obtain sputum culture before starting antibiotics in all hospitalized patients to guide definitive therapy 1
• Perform antimicrobial susceptibility testing immediately, as treatment hinges entirely on resistance patterns 1

Treatment Algorithm Based on Susceptibility

Carbapenem-Susceptible Acinetobacter

• First-line therapy: Imipenem 0.5-1g IV every 6 hours OR meropenem 2g IV every 8 hours with extended infusion 1, 2, 3
• Imipenem is FDA-approved specifically for Acinetobacter species causing lower respiratory tract infections 3
• Use optimal (high) doses to prevent emergence of carbapenem-resistant clones 2

Carbapenem-Resistant Acinetobacter

• Primary therapy: IV polymyxin (colistin) PLUS adjunctive inhaled colistin for respiratory infections 1, 4
• Alternative option: High-dose ampicillin-sulbactam 9-12g/day if the isolate has MIC ≤4 mg/L for sulbactam 1, 2
• Deliver nebulized colistin using ultrasonic or vibrating plate nebulizers 4

When to Use Combination Therapy

Use two active antibiotics when any of the following are present: 1, 2

• Septic shock or high mortality risk
• Severe ventilator-associated pneumonia
• Bacteremia with severe sepsis
• Clinical failure on monotherapy
• Carbapenem-resistant Acinetobacter with severe infection

Specific Combination Recommendations

• For carbapenem-resistant strains with meropenem MIC <8 mg/L, consider combining carbapenem with colistin 1, 2
• Critical caveat: Avoid polymyxin-meropenem combination for isolates with high-level carbapenem resistance (MIC ≥8 mg/L) 1, 4

Duration and Route of Administration

• Start with IV therapy for all hospitalized patients 1
• Continue treatment for at least 2 weeks for severe infections, including ventilator-associated pneumonia and bacteremia 1, 2

Empiric Coverage Indications

Include empiric Acinetobacter coverage when: 1, 4

• Prior colonization with Acinetobacter
• Active outbreak in the facility
• Prolonged ICU stay (>5 days)
• Recent carbapenem or third-generation cephalosporin exposure
• Mechanical ventilation present
• Central venous catheterization

Include a polymyxin in empiric therapy when carbapenem-resistant Acinetobacter is suspected based on local epidemiology 1, 4

Monitoring Requirements

• Monitor renal function regularly when using polymyxins due to significant nephrotoxicity risk 1, 4
• Adjust polymyxin dosing in patients with renal impairment 1, 4
• Be aware that high-dose meropenem increases seizure risk 1, 4

Critical Pitfalls to Avoid

• Never use aminoglycoside monotherapy for Acinetobacter LRTI 4
• Avoid tigecycline, particularly as monotherapy 4
• Do not use ertapenem—it lacks activity against Acinetobacter 2
• Do not use carbapenem monotherapy for severe infections in high-resistance areas 1, 4
• Be aware that heteroresistance to colistin occurs in 18.7-100% of isolates in some series, potentially leading to rapid resistance development during therapy, necessitating close monitoring 1, 2