Bactrim Is Not Effective Against Enterococcus faecalis Infections
Bactrim (trimethoprim-sulfamethoxazole) should not be used to treat Enterococcus faecalis infections as it is ineffective in vivo despite potential in vitro susceptibility. While laboratory testing may sometimes show susceptibility, E. faecalis can escape the antifolate activity of trimethoprim-sulfamethoxazole in the human body by incorporating preformed exogenous folates 1.
Why Bactrim Fails Against E. faecalis
- E. faecalis possesses a unique ability to utilize exogenous folates, allowing it to bypass the mechanism of action of trimethoprim-sulfamethoxazole 1
- Clinical evidence demonstrates treatment failures when Bactrim is used for enterococcal infections, with cases of patients developing bacteremia while on trimethoprim-sulfamethoxazole therapy 1
- The European Society of Cardiology guidelines specifically note that enterococci have intrinsic resistance to several antibiotics, and appropriate treatment requires other agents 2
Recommended Treatment Options for E. faecalis
First-line Treatment
- Ampicillin + gentamicin: Ampicillin 2g IV every 4 hours plus gentamicin 15 mg/kg/day IV/IM in 2-3 divided doses 3
- For penicillin-susceptible strains (MIC ≤8 mg/L), penicillin G or ampicillin combined with gentamicin is the treatment of choice 2
Alternative Regimens
- Ampicillin + ceftriaxone: For aminoglycoside-resistant strains, ampicillin 2g IV every 4 hours plus ceftriaxone 2g IV every 12 hours provides synergistic activity without aminoglycoside toxicity 3
- Vancomycin + gentamicin: For penicillin-allergic patients, vancomycin 30 mg/kg/day IV in 2 divided doses plus gentamicin 15 mg/kg/day IV/IM in 2 divided doses 3
For Vancomycin-Resistant Enterococci (VRE)
- Linezolid 600 mg IV/PO every 12 hours 3
- Daptomycin 8-12 mg/kg IV daily, particularly for bloodstream infections 3
Special Considerations
Duration of Therapy
- Uncomplicated infections: 7-14 days 3
- Native valve endocarditis: 4-6 weeks 3
- Prosthetic valve endocarditis: minimum of 6 weeks 3
Monitoring
- Weekly monitoring of renal function when using aminoglycosides 3
- Regular monitoring of creatine kinase (CK) levels for patients on daptomycin therapy 3
Common Pitfalls to Avoid
- Laboratory reporting pitfall: Clinical microbiology laboratories may report enterococci as susceptible to trimethoprim-sulfamethoxazole based on in vitro testing, which is misleading and potentially dangerous 1
- Relying on in vitro susceptibility alone: Despite apparent susceptibility in laboratory tests, E. faecalis can escape the antifolate activity of trimethoprim-sulfamethoxazole in vivo 1
- Inadequate treatment: Using Bactrim for E. faecalis infections can lead to treatment failure and progression to more serious infections, including bacteremia 1
Urinary Tract Infections
For urinary tract infections specifically, despite some historical use of trimethoprim-sulfamethoxazole for prophylaxis 4, current evidence does not support its use for treatment of enterococcal UTIs. A study of pediatric patients with recurrent UTIs found that enterococci were isolated from almost half of patients, and exposure to antibiotics including trimethoprim-sulfamethoxazole did not effectively prevent enterococcal recurrence 5.
In conclusion, despite potential in vitro activity, Bactrim should not be used to treat E. faecalis infections due to its clinical ineffectiveness and the availability of more reliable treatment options.