What is the oral (PO) amoxicillin dosing for Enterococcus faecalis infections with susceptibility to amoxicillin?

Oral Amoxicillin Dosing for Susceptible Enterococcus faecalis Infections

For susceptible Enterococcus faecalis infections, amoxicillin 500 mg orally three times daily is the recommended oral regimen, achieving effective tissue concentrations for most non-endocarditis infections. 1, 2

Standard Oral Dosing Regimen

• Amoxicillin 500 mg PO three times daily is the established dose for uncomplicated E. faecalis infections in adults, including genitourinary and skin/soft tissue infections 1, 2
• The FDA-approved indication specifically includes E. faecalis (β-lactamase-negative isolates only) for genitourinary tract and skin/skin structure infections 2
• Dosing should be taken at the start of meals to minimize gastrointestinal intolerance 2

Duration of Therapy

• Minimum treatment duration is 7 days for uncomplicated infections such as urogenital sources 1
• Treatment should continue for at least 48-72 hours beyond symptom resolution or evidence of bacterial eradication 2
• For more serious infections requiring initial IV therapy, oral amoxicillin can serve as step-down therapy after clinical improvement 1

Important Clinical Considerations

Susceptibility Requirements

• Oral amoxicillin is appropriate only for β-lactamase-negative E. faecalis strains 2
• If β-lactamase production is detected, switch to amoxicillin-clavulanate (same dosing frequency) 1
• Confirm susceptibility testing before relying on oral therapy for serious infections 1

When Oral Therapy is NOT Appropriate

• Endocarditis requires IV combination therapy (ampicillin 200-300 mg/kg/day IV divided every 4-6 hours plus gentamicin for adults, or ampicillin-ceftriaxone combinations) and cannot be treated with oral amoxicillin alone 3, 4
• Bacteremia in patients with acute kidney injury requires IV linezolid or daptomycin, not oral amoxicillin 5
• Orthopedic/prosthetic infections require prolonged IV synergistic combinations initially 6

Pediatric Dosing Considerations

• For pediatric patients ≥3 months with susceptible E. faecalis, standard dosing follows weight-based calculations per FDA labeling 2
• The guideline-recommended IV dose for serious pediatric infections is ampicillin 200-300 mg/kg/day divided every 4-6 hours (up to 12 g daily), which can inform oral step-down dosing proportionally 3

Common Pitfalls to Avoid

• Do not underdose: The full 500 mg three times daily (1500 mg total daily) is necessary for adequate tissue penetration 1
• Do not confuse colonization with infection: E. faecalis presence without clinical signs does not require treatment 1
• Do not use for vancomycin-resistant strains: These require linezolid 600 mg PO every 12 hours instead 1
• Do not assume all enterococci are E. faecalis: E. faecium has different resistance patterns and may not respond to amoxicillin 3

Alternative Oral Options for Penicillin Allergy

• Nitrofurantoin 100 mg PO every 6 hours for 7 days (for urinary tract sources only) 1
• Fosfomycin 3 g PO single dose (for uncomplicated urinary infections) 1
• Linezolid 600 mg PO every 12 hours (for resistant strains or severe penicillin allergy) 5, 1