What is the recommended treatment for a hospitalized or immunocompromised patient suspected of having an Acinetobacter iwoffii infection?

Treatment of Acinetobacter iwoffii Infection in Hospitalized or Immunocompromised Patients

Treat Acinetobacter iwoffii with the same aggressive antimicrobial approach as A. baumannii complex infections, starting with carbapenem monotherapy (imipenem, meropenem, or doripenem) if local carbapenem resistance is low, or polymyxin-based therapy if resistance is high. 1

Critical Initial Recognition and Infection Control

Implement contact precautions immediately upon identification of any Acinetobacter species, as routine clinical laboratories do not need to distinguish between A. iwoffii and A. baumannii for treatment purposes—all Acinetobacter species causing infection in hospitalized patients warrant identical aggressive therapy. 1

• Institute alert codes in the electronic medical record to identify the patient promptly if readmitted 1
• Clean all room surfaces and medical equipment with 0.5% hypochlorite solutions 1
• Screen for colonization weekly during outbreaks using rectal and pharyngeal swabs, plus tracheal secretions in ventilated patients 2

Empirical Treatment Algorithm

When to Cover Acinetobacter Empirically

Start empirical Acinetobacter coverage in severe infections (severe sepsis or septic shock) when any of these conditions exist: 2

• Active Acinetobacter outbreak in your facility
• Endemic Acinetobacter in your ICU setting
• Patient previously colonized with Acinetobacter
• Prolonged ICU stay with mechanical ventilation
• Recent carbapenem or third-generation cephalosporin exposure within 90 days

Empirical Antibiotic Selection

In areas with <25% carbapenem resistance: Start carbapenem monotherapy immediately 2

• Imipenem 0.5-1g IV every 6 hours, OR
• Meropenem 2g IV every 8 hours as extended infusion (preferred), OR
• Doripenem 500mg IV every 8 hours 3

In areas with ≥25% carbapenem resistance or during outbreaks: Include a polymyxin in the empirical regimen 2

• Colistin: loading dose 9 million IU, then 4.5 million IU IV every 12 hours (adjust for renal function) 4

For severe sepsis or septic shock: Use combination therapy with two agents regardless of resistance patterns 4

Definitive Treatment Based on Susceptibility Results

Carbapenem-Susceptible Isolates

Use carbapenem monotherapy as first-line treatment: 2, 1

• Imipenem, meropenem, or doripenem at doses listed above
• Continue for 2 weeks for bacteremia or severe infections 1
• Shorter courses (7-10 days) acceptable only for less severe, localized infections 2

Carbapenem-Resistant Isolates

First choice: Ampicillin-sulbactam if sulbactam MIC ≤4 mg/L 1, 4

• Dose: 3g sulbactam component every 8 hours as 4-hour infusion (9-12g/day total) 2, 4
• Superior mortality outcomes compared to polymyxins with lower nephrotoxicity (15% vs 33%) 4

Second choice: Intravenous polymyxin for isolates resistant to both carbapenems and sulbactam 1

• Colistin dosing as above, weight-based and renally adjusted 4

Combination Therapy Indications

Use two active agents when: 2, 3

• Septic shock present
• Severe ventilator-associated pneumonia
• Bacteremia with severe sepsis
• Clinical failure on monotherapy after 48-72 hours
• Carbapenem-resistant isolate with severe infection

Effective combinations: 2

• Polymyxin + carbapenem (if meropenem MIC <8 mg/L)
• Polymyxin + sulbactam
• Polymyxin + tigecycline (loading 200mg, then 100mg every 12 hours)

Avoid these combinations: 2, 4

• Colistin + rifampin (no proven clinical benefit, increases hepatotoxicity)
• Colistin + vancomycin (increased nephrotoxicity without benefit)
• Polymyxin + meropenem if MIC >16 mg/L (no benefit)

Special Considerations for Respiratory Infections

For ventilator-associated pneumonia or severe lower respiratory tract infection: 2, 3

• Add nebulized colistin 5 million IU every 8 hours using vibrating plate nebulizer 2
• Continue IV therapy concurrently—nebulized therapy is adjunctive only 3
• Consider nebulized aminoglycosides (tobramycin or amikacin) as alternative 2

Treatment Duration

For bacteremia or severe infections (septic shock, VAP): 14 days minimum 2, 1

For less severe localized infections: 7-10 days may be acceptable, but monitor closely for relapse 2

Critical Monitoring Requirements

Renal function monitoring is mandatory: 1, 4

• Check serum creatinine every 48-72 hours during polymyxin therapy
• Nephrotoxicity occurs in 33-54% of colistin-treated patients 4
• Adjust polymyxin dosing immediately when creatinine rises

Clinical response assessment: 1

• Repeat blood cultures at 48-72 hours to document clearance in bacteremia
• Consider treatment failure if no improvement by day 3-5

Absolute Contraindications and Critical Pitfalls

Never use these approaches: 1, 4

• Tigecycline monotherapy for bacteremia (suboptimal serum levels, high failure rates)
• Aminoglycoside monotherapy for serious infections
• Ertapenem for any Acinetobacter infection (lacks activity against this genus)
• Carbapenem monotherapy in endemic areas without susceptibility confirmation
• Delayed empirical coverage in previously colonized patients with severe sepsis

Antibiotic Stewardship Essentials

De-escalate therapy once susceptibilities return: 1

• Narrow from combination to monotherapy if isolate susceptible
• Switch from polymyxin to carbapenem or sulbactam when possible
• Discontinue empirical coverage if cultures negative at 48 hours

Implement antibiotic stewardship program involvement: 2

• Mandatory for controlling resistance emergence
• Review all Acinetobacter cases for appropriateness of therapy
• Monitor local resistance patterns quarterly to guide empirical choices