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 every 6 hours or meropenem 2g every 8 hours as extended infusion; for carbapenem-resistant strains, use intravenous polymyxin (colistin) with adjunctive inhaled colistin for respiratory infections. 1, 2

Initial Diagnostic Approach

• Obtain sputum culture before starting antibiotics in all hospitalized patients with suspected Acinetobacter LRTI 3, 2
• Perform antimicrobial susceptibility testing immediately to guide definitive therapy 1, 2
• The FDA approves imipenem/cilastatin specifically for LRTI caused by Acinetobacter species 4

Treatment Algorithm Based on Susceptibility

For Carbapenem-Susceptible Acinetobacter

First-line therapy:

• Imipenem 0.5-1g IV every 6 hours 1
• Meropenem 2g IV every 8 hours (extended infusion preferred) 1, 2
• Doripenem is an alternative carbapenem option 2, 5

The carbapenems remain the drugs of choice when susceptibility is confirmed 1, 2, 5. Use high doses to prevent emergence of resistant clones 2.

For Carbapenem-Resistant Acinetobacter

Primary therapy:

• Intravenous polymyxin (colistin) is strongly recommended 1, 2
• Add adjunctive inhaled colistin for ventilator-associated pneumonia or severe respiratory infections 1, 2
• Deliver nebulized antibiotics using ultrasonic or vibrating plate nebulizers 1

Alternative for sulbactam-susceptible strains:

• High-dose ampicillin-sulbactam 9-12g/day if MIC ≤4 mg/L 2
• However, recent data shows Acinetobacter is highly resistant to sulbactam in many regions 6

Combination Therapy Indications

Use two active antibiotics when: 1, 2

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

For carbapenem-resistant strains with meropenem MIC <8 mg/L, consider combining carbapenem with colistin 2. However, avoid polymyxin-meropenem combination for isolates with high-level carbapenem resistance 1.

Route of Administration and Duration

• Start with IV therapy for hospitalized patients 3
• Continue treatment for at least 2 weeks for severe infections including ventilator-associated pneumonia and bacteremia 2
• Switch from IV to oral is not typically applicable for Acinetobacter LRTI given limited oral options 3

Monitoring Requirements

• Monitor renal function regularly when using polymyxins due to nephrotoxicity risk 1
• Adjust polymyxin dosing in patients with renal impairment 1
• Be aware that high-dose meropenem may increase seizure risk 1
• Colistin remains universally susceptible in most studies (MIC ≤1 μg/ml) 7

Critical Pitfalls to Avoid

Do not use: 1

• Aminoglycoside monotherapy for Acinetobacter infections
• Tigecycline, particularly as monotherapy
• Ertapenem (lacks activity against Acinetobacter) 2
• Carbapenem monotherapy for severe infections in high-resistance areas 1

Empiric Coverage Considerations

Include empiric Acinetobacter coverage when: 2

• Prior colonization with Acinetobacter species
• Active outbreak in the facility
• Prolonged ICU stay with multiple invasive procedures
• Recent carbapenem or third-generation cephalosporin exposure
• Mechanical ventilation or central venous catheterization present

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

Resistance Considerations

• Carbapenem resistance is extremely high (87.5-96.4%) in many healthcare settings 7
• The most common resistance mechanism is blaOXA-23-like gene, followed by blaNDM-1 7
• Heteroresistance to colistin occurs in 18.7-100% of isolates in some series, potentially leading to rapid resistance development during therapy 2
• Biofilm formation contributes to environmental persistence and treatment difficulty 7

Special Circumstances

For ventilator-associated pneumonia specifically, consider aerosolized antibiotics (colistin or aminoglycosides) as adjunctive therapy for highly resistant strains or clinical failures 2. The combination of IV plus inhaled colistin is recommended for carbapenem-resistant Acinetobacter VAP 1.