Treatment of Acinetobacter iwoffii Infections
Carbapenems are the drugs of choice for treating Acinetobacter iwoffii infections, with imipenem, meropenem, or doripenem being the preferred agents. 1
First-Line Treatment Options
Carbapenem-Susceptible A. iwoffii
- Carbapenems: Imipenem, meropenem, or doripenem (except ertapenem which lacks activity against Acinetobacter species) 1
- Meropenem: 2g every 8 hours (extended infusion recommended)
- Imipenem: 0.5-1g every 6 hours 2
Carbapenem-Resistant A. iwoffii
For isolates with carbapenem resistance, the following options should be considered:
Polymyxins (colistin or polymyxin B) 1, 2
- Colistin: Loading dose 6-9 million IU, then 9 million IU/day in 2-3 doses
- Polymyxin B: Loading dose 2-2.5 mg/kg, then 1.5-3 mg/kg/day in 2 doses 2
Sulbactam-containing regimens (e.g., ampicillin-sulbactam) 1, 2
- Sulbactam: 9-12 g/day in 3 daily doses (4-hour infusion recommended) 2
Tigecycline (except for pneumonia, bloodstream infections, or urinary tract infections) 2
- Standard dose: 100 mg loading, then 50 mg q12h
- High dose: 200 mg loading, then 100 mg q12h 2
Aminoglycosides (if susceptible) in combination with other agents 1
Combination Therapy Considerations
For severe infections or those caused by multidrug-resistant strains:
- Combination therapy with two in vitro active antibiotics among polymyxins, aminoglycosides, tigecycline, or sulbactam combinations is recommended 2
- For respiratory infections, consider adjunctive inhaled colistin in addition to systemic therapy 2
- Although some studies have explored polymyxin combinations with carbapenems, rifampicin, or azithromycin, synergy is highly strain-dependent and not consistently demonstrated 3
Treatment Duration
- Severe infections (e.g., ventilator-associated pneumonia): 7-14 days 2
- Less severe infections: Shorter durations may be appropriate
- Complicated urinary tract infections: 5 days 2
Special Considerations
Empiric Coverage
Empiric coverage for A. iwoffii is recommended in:
- Severe infections occurring during an Acinetobacter outbreak
- Endemic situations
- Previously colonized patients 1
Monitoring and Adjustments
- Assess clinical response within 48-72 hours of treatment initiation
- Monitor renal function regularly, especially with polymyxins and carbapenems
- Adjust dosing based on minimum inhibitory concentration (MIC) of the isolate 2
Heteroresistance
- Heteroresistance to colistin and carbapenems has been reported in Acinetobacter species
- Microdilution methods may not adequately detect heteroresistant populations 1
- Consider this possibility in cases of treatment failure despite apparent in vitro susceptibility
Treatment Challenges
Acinetobacter iwoffii, like other Acinetobacter species, can rapidly develop resistance to multiple antibiotics 4, 5. The treatment of these infections is challenging due to:
- Limited therapeutic options for multidrug-resistant strains
- Potential for development of resistance during therapy
- Biofilm formation requiring higher antibiotic concentrations
- Risk of nephrotoxicity with polymyxins
The optimal treatment for A. iwoffii infections requires knowledge of local susceptibility patterns and should be guided by antimicrobial susceptibility testing whenever possible 4.