What is the recommended treatment for an Enterococcus faecium urinary tract infection (UTI) that is sensitive to ampicillin?

Treatment of Ampicillin-Susceptible Enterococcus faecium UTI

Ampicillin is the definitive drug of choice for ampicillin-susceptible Enterococcus faecium urinary tract infections. 1, 2

Recommended Treatment Regimen

For Uncomplicated UTI (Oral Therapy)

• Amoxicillin 500 mg orally every 8 hours for 7 days is the preferred first-line oral therapy, achieving clinical cure rates of 88.1% and microbiological eradication rates of 86% 2, 3
• Ampicillin 500 mg orally every 8 hours for 7 days is an equivalent alternative with similar efficacy 2, 3

For Complicated UTI or Hospitalized Patients (IV Therapy)

• High-dose ampicillin 2 g IV every 4-6 hours (18-30 g daily in divided doses) is recommended to achieve sufficient urinary concentrations 2, 4
• The FDA label specifically indicates ampicillin for urinary tract infections caused by susceptible organisms 4

Catheter-Associated UTI Considerations

• Remove the indwelling catheter if clinically feasible, as catheter retention is strongly associated with treatment failure 1
• If catheter removal is not possible, consider antibiotic lock therapy in addition to systemic ampicillin therapy 1
• Treatment duration should be 7-14 days for catheter-associated enterococcal UTI 1

Critical Clinical Decision Points

Confirm True Infection vs. Colonization

• Do not treat asymptomatic bacteriuria, which is extremely common in catheterized patients and treatment fosters antimicrobial resistance 1, 3
• Ensure the patient has symptomatic infection with fever, dysuria, urgency, or systemic signs before initiating therapy 1

Monitor for Complicated Infection

• Evaluate for signs of upper tract involvement including fever, rigors, flank pain, or delirium that would warrant longer therapy 1
• If persistent bacteremia occurs despite appropriate therapy, obtain transesophageal echocardiography to evaluate for endocarditis 1

Alternative Oral Agents (If Ampicillin Cannot Be Used)

• Nitrofurantoin 100 mg orally every 6 hours for 7 days has excellent activity against E. faecium with resistance rates below 6% 2, 3, 5
• Fosfomycin 3 g orally as a single dose is FDA-approved specifically for E. faecalis UTI and provides convenient single-dose therapy for uncomplicated infections 2, 3, 5

Common Pitfalls to Avoid

• Do not use fluoroquinolones despite reported susceptibility, as clinical outcomes are poor and resistance rates are high (46-47% for ciprofloxacin/levofloxacin) 2, 3
• Do not ignore the catheter - failure to address the indwelling catheter significantly increases treatment failure rates 1
• Do not assume resistance based solely on species - E. faecium can be ampicillin-susceptible, particularly clade B and A2 strains, which differ from the typically resistant clade A1 hospital-associated strains 6

Unique Pharmacokinetic Advantage

• High urinary concentrations of ampicillin can overcome elevated MICs, making it effective even when in vitro susceptibility testing suggests borderline resistance 2, 7
• This pharmacokinetic property is specific to urinary tract infections and does not apply to other infection sites 7