Is Bactrim (trimethoprim/sulfamethoxazole) effective against Pseudomonas aeruginosa?

Bactrim Does Not Cover Pseudomonas Aeruginosa

Bactrim (trimethoprim/sulfamethoxazole) is not effective against Pseudomonas aeruginosa and should not be used for infections where this pathogen is suspected or confirmed. This is clearly established in current clinical guidelines and research evidence.

Antimicrobial Coverage for Pseudomonas aeruginosa

Effective Antibiotics for Pseudomonas

According to current guidelines, the following antibiotics have reliable activity against P. aeruginosa 1:

• Antipseudomonal β-lactams:

  • Piperacillin-tazobactam (3.375g IV q6h or 4.5g IV q6h)
  • Ceftazidime (2g IV q8h)
  • Cefepime (2g IV q8-12h)
  • Meropenem (1g IV q8h)
  • Imipenem/cilastatin (500mg IV q6h or 1g IV q8h)
  • Doripenem (500mg IV q8h)
  • Aztreonam (1-2g IV q6-8h)

• Fluoroquinolones:

  • Ciprofloxacin (400mg IV q12h or 750mg PO q12h)
  • Levofloxacin (750mg IV/PO q24h)

• Aminoglycosides:

  • Amikacin (15-20mg/kg IV q24h)
  • Gentamicin (5-7mg/kg IV q24h)
  • Tobramycin (5-7mg/kg IV q24h)

• Other agents:

  • Colistin (for resistant strains)

Bactrim's Limitations Against Pseudomonas

The evidence clearly shows that Bactrim lacks reliable activity against P. aeruginosa:

1. In the 2017 World Society of Emergency Surgery guidelines for intra-abdominal infections, it is explicitly stated that certain antibiotics "are effective against P. aeruginosa, but [others] are ineffective against anaerobic bacteria and need association with metronidazole" 2. Bactrim is not listed among the effective agents against Pseudomonas.

2. The European Respiratory Society guidelines for hospital-acquired pneumonia specifically recommend antipseudomonal agents including "imipenem, meropenem, cefepime, piperacillin/tazobactam, levofloxacin or ceftazidime" for coverage of P. aeruginosa 2. Bactrim is not included in these recommendations.

3. Research from 1977 showed that while some strains of P. aeruginosa were "moderately resistant" to sulfamethoxazole, 16% were "highly resistant" with MICs greater than 1000 μg/ml 3. Even for the moderately resistant strains, the concentrations needed for synergy between trimethoprim and sulfamethoxazole were at the upper limits of achievable urinary concentrations.

Clinical Implications

When Treating Suspected Pseudomonas Infections

• Always select an agent with reliable antipseudomonal activity
• For empiric therapy of serious infections where Pseudomonas is suspected, use an antipseudomonal β-lactam (such as piperacillin-tazobactam, cefepime, or a carbapenem) 2
• For critically ill patients, consider dual pseudomonal coverage with an antipseudomonal β-lactam plus either an aminoglycoside or fluoroquinolone 2

Common Pitfalls to Avoid

• Do not use Bactrim for empiric coverage of suspected Pseudomonas infections - this could lead to treatment failure and increased mortality
• Do not confuse Pseudomonas aeruginosa with Stenotrophomonas maltophilia (formerly Pseudomonas maltophilia), which is often susceptible to Bactrim 4
• Be aware that some studies have shown synergy between Bactrim and other agents against certain gram-negative bacteria, but this does not reliably extend to P. aeruginosa 5

Special Considerations

For cystic fibrosis patients with P. aeruginosa infections, guidelines recommend specific antipseudomonal regimens:

• High-dose antipseudomonal antibiotics
• Often combination therapy to prevent resistance
• Consideration of nebulized antibiotics (colistin or tobramycin) 2, 1

In conclusion, when treating infections where P. aeruginosa is suspected or confirmed, clinicians should select antibiotics with established activity against this pathogen, which does not include Bactrim.