Will oral (PO) amoxicillin cover an Enterococcus urinary tract infection (UTI) that is sensitive to ampicillin?

Oral Amoxicillin for Ampicillin-Sensitive Enterococcal UTI

Yes, oral amoxicillin is effective for treating enterococcal UTIs that are sensitive to ampicillin. According to the FDA label, amoxicillin is specifically indicated for genitourinary tract infections due to susceptible isolates of Enterococcus faecalis 1.

Evidence Supporting Amoxicillin for Enterococcal UTIs

FDA Approval and Guidelines

• The FDA explicitly approves oral amoxicillin for "infections of the genitourinary tract due to susceptible (ONLY β-lactamase–negative) isolates of Enterococcus faecalis" 1
• The Infectious Diseases Society of America (IDSA) guidelines state that "ampicillin is the drug of choice for ampicillin-susceptible enterococci" 2

Pharmacological Considerations

• Amoxicillin and ampicillin belong to the same class of aminopenicillins with similar antimicrobial activity
• Amoxicillin achieves high urinary concentrations, making it effective for lower urinary tract infections
• Recent research indicates that aminopenicillins can achieve bacterial eradication and clinical cure in lower urinary tract infections due to their high urinary concentrations 3

Treatment Approach for Enterococcal UTIs

Dosing and Duration

• For uncomplicated enterococcal UTIs, a 7-14 day course of therapy is recommended 2
• Standard dosing of amoxicillin for adults with UTIs should follow FDA guidelines 1

Monitoring Response

• Monitor clinical response within 72 hours of initiating therapy 4
• If symptoms persist beyond 72 hours despite appropriate therapy, consider:
  • Extending treatment duration
  • Performing urologic evaluation
  • Adjusting antimicrobial regimen based on culture and susceptibility results 4

Important Considerations

Confirm True Infection vs. Colonization

• Ensure the patient has symptoms of UTI and not just asymptomatic bacteriuria
• A high colony count (>100,000 cfu/ml) in a urine specimen suggests true infection 4
• Treatment is only indicated for symptomatic UTI 4

Alternative Options if Amoxicillin Cannot Be Used

If the enterococcal isolate is resistant to ampicillin/amoxicillin:

• Vancomycin is recommended for ampicillin-resistant enterococci 2
• For uncomplicated lower UTIs caused by vancomycin-resistant enterococci (VRE), options include:
  • Nitrofurantoin
  • Fosfomycin
  • Doxycycline 5, 6

Catheter Considerations

• If an indwelling catheter has been in place for ≥2 weeks, replace the catheter to hasten symptom resolution 4
• Obtain urine culture specimens from freshly placed catheters prior to initiating antimicrobial therapy 4
• Discontinue urinary catheters as soon as possible 4

Pitfalls to Avoid

1. Treating asymptomatic bacteriuria: Avoid treating patients who are simply colonized with enterococci in the urine but not infected 5
2. Inadequate treatment duration: Ensure complete eradication with appropriate treatment length
3. Failure to remove or replace catheters: This can lead to persistent infection
4. Overlooking susceptibility testing: Always confirm susceptibility to ampicillin before using amoxicillin

In conclusion, oral amoxicillin is an appropriate and effective treatment for enterococcal UTIs when the isolate is confirmed to be sensitive to ampicillin.