Rifampin Should Not Be Added to Amoxicillin for Treating Enterococcus faecalis Infections
Adding rifampin to amoxicillin is not recommended for treating Enterococcus faecalis infections as there is no clinical benefit and it may actually antagonize treatment efficacy. 1
Evidence Against Adding Rifampin
- The European Society of Cardiology guidelines explicitly state there is "no clinical benefit of adding rifampicin" in the treatment of enterococcal infections 2, 1
- In vitro studies demonstrate that rifampin can actually decrease the activity of other antibiotics against E. faecalis, showing antagonistic effects rather than synergistic ones 3
- Laboratory research shows that adding rifampin delayed the bactericidal activity of daptomycin against E. faecalis biofilms 3
- Rifampin is primarily recommended for staphylococcal infections, particularly in prosthetic device infections, not for enterococcal infections 1
First-Line Treatment for E. faecalis Infections
- For beta-lactam and gentamicin-susceptible E. faecalis strains, the recommended first-line treatment is amoxicillin/ampicillin (200 mg/kg/day IV) combined with gentamicin (3 mg/kg/day) 2, 1
- An effective alternative regimen for E. faecalis, including high-level aminoglycoside resistant strains, is ampicillin (200 mg/kg/day) plus ceftriaxone (4 g/day) 2, 1
- For patients with penicillin allergies, vancomycin (30 mg/kg/day) plus gentamicin is recommended 2, 1
Research on Rifampin with E. faecalis
- In experimental models using biofilm-forming E. faecalis, the addition of rifampin decreased the activity of daptomycin against both E. faecalis and vancomycin-resistant enterococci 3
- Studies show inconsistent results regarding rifampin's role in treating E. faecalis infections, with some showing antagonism and others showing limited benefit in specific combinations 4, 5
- One study found that rifampin alone showed no activity on planktonic or adherent E. faecalis in a foreign-body infection model 4
- The combination of rifampin with daptomycin or fosfomycin showed limited efficacy, curing only 17% and 25% of cases respectively in an experimental model 4
Important Clinical Considerations
- When treating E. faecalis infections, it's crucial to avoid confusing treatment regimens for staphylococcal and enterococcal infections - rifampin is standard for staphylococcal prosthetic valve endocarditis but not for enterococcal infections 2, 1
- Using rifampin alone is associated with a high frequency of microbial resistance development and should be avoided 2, 1
- For prosthetic joint infections involving E. faecalis, the recommended oral antibiotic regimen is amoxicillin without rifampin 2
- The disparity between some in vitro and in vivo results regarding rifampin combinations raises doubts about the relevance of certain laboratory observations to clinical outcomes 6
Alternative Approaches for Difficult-to-Treat E. faecalis Infections
- For multi-resistant strains, consider daptomycin plus ampicillin, linezolid, or quinupristin-dalfopristin (not for E. faecalis) 2, 1
- In cases of biofilm-forming E. faecalis, the addition of gentamicin to daptomycin in the first 24 hours has been shown to significantly improve bactericidal activity 3
- For high-level aminoglycoside resistant E. faecalis endocarditis, the combination of ampicillin plus ceftriaxone is the treatment of choice 2, 1