Treatment of Pyelonephritis Caused by Enterococcus faecalis
For pyelonephritis caused by Enterococcus faecalis in adults without beta-lactam allergy, ampicillin monotherapy (2g IV every 4-6 hours) is the first-line treatment, with a duration of 10-14 days. 1, 2
Primary Treatment Approach
Ampicillin remains the drug of choice for E. faecalis infections when the organism is susceptible (penicillin MIC ≤8 mg/L), with high-dose regimens of 18-30g IV daily in divided doses recommended to achieve sufficient therapeutic concentrations. 2
For pyelonephritis specifically, ampicillin 2g IV every 4-6 hours for 10-14 days is the standard regimen, as beta-lactam agents require this extended duration compared to other antimicrobials. 1
If the patient can tolerate oral therapy and the organism is confirmed susceptible, amoxicillin 500mg PO every 8 hours can be used to complete the treatment course. 2
Alternative Regimens When Ampicillin Alone is Insufficient
For severe pyelonephritis requiring hospitalization or if bacteremia is suspected, consider adding gentamicin (if aminoglycoside-susceptible) to ampicillin for synergistic bactericidal activity, though this is more commonly reserved for endocarditis than uncomplicated pyelonephritis. 1, 2
If the isolate demonstrates high-level aminoglycoside resistance (HLAR), the double beta-lactam combination of ampicillin 2g IV every 4 hours PLUS ceftriaxone 2g IV every 12 hours provides excellent bactericidal activity with lower nephrotoxicity risk compared to aminoglycoside-containing regimens. 3, 4
Important Clinical Considerations
E. faecalis is generally ampicillin-susceptible (only ~3% are multidrug-resistant), making it much more amenable to treatment than E. faecium. 2
Always obtain susceptibility testing to confirm ampicillin susceptibility and guide definitive therapy, as empiric coverage should be tailored once culture results are available. 1
Avoid cephalosporins as monotherapy (except in double beta-lactam regimens with ampicillin), as most cephalosporins have poor activity against enterococci. 2
Nitrofurantoin should NOT be used for pyelonephritis despite its excellent activity against E. faecalis in cystitis, as it achieves inadequate tissue concentrations for upper urinary tract infections. 2
When to Consider Vancomycin
- Vancomycin 30 mg/kg per 24h IV in 2 divided doses should be reserved for patients with documented beta-lactam allergy or ampicillin-resistant strains, though resistance rates remain low in E. faecalis. 2
Duration and Monitoring
10-14 days of therapy is required when using beta-lactam agents for pyelonephritis, which is longer than the 5-7 day courses used for fluoroquinolones. 1
Monitor renal function if aminoglycosides are added, as nephrotoxicity occurs in approximately 23% of patients receiving ampicillin-gentamicin combinations. 1, 3