Is Bactrim (trimethoprim/sulfamethoxazole) an appropriate treatment for Acinetobacter lwoffii infections?

Bactrim is NOT an Appropriate Treatment for Acinetobacter lwoffii Infections

Bactrim (trimethoprim/sulfamethoxazole) should not be used as first-line treatment for Acinetobacter lwoffii infections due to high rates of resistance and availability of more effective alternatives.

Treatment Options for Acinetobacter lwoffii

Acinetobacter lwoffii is a gram-negative bacterium that has emerged as an opportunistic pathogen, particularly in healthcare settings. When selecting treatment for A. lwoffii infections, several factors must be considered:

First-Line Treatment Options

1. Carbapenems

   • In areas with low carbapenem resistance: Carbapenems (imipenem, meropenem) are the drugs of choice for Acinetobacter infections 1
   • Recommended dosing: Imipenem 0.5-1g every 6 hours or Meropenem 2g every 8 hours 1

2. Sulbactam-containing regimens

   • Sulbactam has intrinsic activity against Acinetobacter species and may be effective for isolates with MIC ≤4 mg/L 1
   • Recommended dosing: 9-12g/day of sulbactam in 3 daily doses, with 4-hour infusion recommended 1
   • Clinical outcomes with ampicillin-sulbactam have been comparable to carbapenems in several studies 1

3. Polymyxins (Colistin or Polymyxin B)

   • For carbapenem-resistant Acinetobacter infections 1
   • Intravenous polymyxins are strongly recommended for carbapenem-resistant isolates 1
   • Consider adjunctive inhaled colistin for respiratory infections 1

Why Bactrim is Not Appropriate

Trimethoprim/sulfamethoxazole (TMP-SMX) has several limitations for Acinetobacter lwoffii treatment:

1. High resistance rates: Non-susceptibility rates for Acinetobacter species to TMP-SMX range from 4% to 98.2%, with most studies reporting >70% non-susceptibility 2

2. Particularly poor activity against resistant strains: Carbapenem-resistant Acinetobacter species have non-susceptibility rates to TMP-SMX of >80% in most studies 2

3. Limited clinical evidence: There are only a few case reports evaluating TMP-SMX for Acinetobacter infections, mainly in combination with other agents 2

4. Not recommended in guidelines: Major guidelines for Acinetobacter infections do not include TMP-SMX as a primary treatment option 1

Special Considerations

For Multidrug-Resistant (MDR) A. lwoffii

For MDR isolates, treatment options may include:

1. Combination therapy with two active agents when possible 3
2. Imipenem (57% sensitivity reported in one NICU study) 4
3. TMP-SMX as last resort: May only be considered when no other options are available and susceptibility is confirmed 2

Risk Factors for A. lwoffii Infections

Be vigilant in patients with:

• Immunosuppression
• Prolonged hospitalization
• Previous antimicrobial therapy
• Multiple invasive procedures
• Prior colonization with Acinetobacter species 1
• Premature and very low birth weight neonates 4

Treatment Algorithm

1. Obtain cultures and susceptibility testing before initiating therapy
2. Empiric therapy (if Acinetobacter suspected):
   • Carbapenem (in areas with low resistance)
   • Polymyxin (in areas with high carbapenem resistance)
3. Directed therapy (once susceptibilities known):
   • Use carbapenem if susceptible
   • Use sulbactam-containing regimen if susceptible (MIC ≤4 mg/L)
   • Use polymyxin if resistant to above options
   • Consider TMP-SMX only if susceptible and no other options available

Pitfalls to Avoid

1. Empiric use of TMP-SMX: Due to high resistance rates, empiric TMP-SMX is not recommended for suspected Acinetobacter infections
2. Monotherapy for severe infections: Consider combination therapy for severe infections, especially with MDR strains
3. Delayed treatment: Prompt initiation of appropriate antimicrobial therapy is crucial for reducing mortality
4. Failure to adjust therapy based on susceptibilities: Always reassess treatment when culture results become available

In conclusion, while TMP-SMX might occasionally show in vitro activity against some Acinetobacter lwoffii isolates, it should not be considered a reliable treatment option due to widespread resistance and the availability of more effective alternatives with better clinical evidence.