What is the oral antibiotic of choice for complicated urinary tract infection (UTI) caused by enterococcus?

Oral Antibiotic Options for Enterococcus Complicated UTI

For complicated UTIs caused by enterococcus, fosfomycin (3g single dose) is the oral antibiotic of choice due to its excellent efficacy against vancomycin-resistant enterococci (VRE) and favorable safety profile. 1

First-Line Options (in order of preference)

1. Fosfomycin

   • Dosing: 3g oral single dose 1
   • Advantages: Minimal drug interactions, highly effective against enterococci including VRE 1
   • Consider for uncomplicated lower UTI caused by VRE 2

2. Nitrofurantoin

   • Dosing: 100mg PO every 6 hours 2
   • Recommended for uncomplicated UTIs due to VRE 2
   • Contraindications: Renal impairment (CrCl <60 mL/min) 1

3. Amoxicillin/Ampicillin

   • Dosing: Amoxicillin 500mg PO every 8 hours 2
   • Recommended for ampicillin-susceptible enterococcal UTIs, including VRE 3
   • High-dose ampicillin can be used for uncomplicated UTIs due to VRE 2

Second-Line Options

1. Linezolid

   • Dosing: 600mg PO every 12 hours 2
   • Strong recommendation for enterococcal infections 2
   • Duration depends on site of infection and clinical response 2
   • Recent evidence shows 92.6% response rate in VRE infections 4
   • Consider monitoring for thrombocytopenia with longer treatment courses 4

2. Doxycycline

   • Has intrinsic activity against enterococci, including VRE 3
   • Possible oral option for VRE cystitis 3

Treatment Algorithm

1. Obtain urine culture and susceptibility testing before initiating therapy

   • Essential to guide appropriate antibiotic selection 1

2. For initial empiric therapy (pending cultures):

   • If low suspicion for resistance: Fosfomycin 3g single dose OR Nitrofurantoin 100mg PO q6h
   • If high suspicion for resistance (healthcare-associated, recent antibiotics): Consider linezolid 600mg PO q12h

3. Once susceptibilities are available:

   • If ampicillin-susceptible: Use amoxicillin 500mg PO q8h
   • If ampicillin-resistant but nitrofurantoin/fosfomycin-susceptible: Use either nitrofurantoin or fosfomycin
   • If multi-drug resistant: Use linezolid 600mg PO q12h

4. Treatment duration:

   • Fosfomycin: Single 3g dose
   • Nitrofurantoin: 5-7 days
   • Amoxicillin/ampicillin: 5-7 days
   • Linezolid: 7-14 days (based on clinical response)

Special Considerations

• Vancomycin-resistant enterococci (VRE): Fosfomycin, nitrofurantoin, and linezolid are effective options 2, 3
• Renal impairment: Avoid nitrofurantoin if CrCl <60 mL/min 1
• Severe infection/upper UTI: Consider parenteral therapy initially with linezolid or daptomycin 3
• Asymptomatic bacteriuria: Treatment not recommended unless in pregnant women or before invasive urologic procedures 1, 3

Monitoring

• Monitor clinical response within 48-72 hours
• For linezolid: Monitor complete blood count weekly if treatment extends beyond 14 days due to risk of thrombocytopenia 4
• Follow-up urine culture may be warranted in complicated cases or treatment failures

Pitfalls to Avoid

• Treating asymptomatic bacteriuria with enterococci, which is common and rarely requires treatment 5
• Using fluoroquinolones empirically due to increasing resistance rates 1
• Failing to remove urinary catheters when possible, as they serve as a nidus for infection 6
• Using linezolid for extended periods without monitoring for hematologic toxicity 3

Remember that enterococci are a common cause of UTIs among hospitalized patients, and the rising prevalence of VRE is concerning due to limited treatment options and association with increased mortality and healthcare costs 3.