What is the recommended treatment for a urinary tract infection caused by Enterococcus faecium resistant to nitrofurantoin, ampicillin, and ciprofloxacin?

Treatment for Multi-Drug Resistant Enterococcus faecium UTI

For this woman with a complicated urinary tract infection caused by multi-drug resistant Enterococcus faecium (resistant to nitrofurantoin, ampicillin, and ciprofloxacin), linezolid 600 mg IV or PO every 12 hours for 5-7 days is the recommended treatment. 1

Primary Treatment Recommendation

Linezolid is the first-line agent for complicated UTIs caused by vancomycin-resistant or multi-drug resistant enterococci, with strong guideline support and demonstrated efficacy. 1

• Linezolid 600 mg IV or PO every 12 hours is specifically recommended for complicated urinary tract infections due to resistant enterococci, with treatment duration of 5-7 days based on clinical response 1
• This agent has bacteriostatic activity against both E. faecium and E. faecalis with excellent in vitro susceptibility (MIC90 = 2-4 mcg/mL) 2
• Clinical cure rates of 92.6% have been demonstrated in VRE infections at various sites 2

Alternative Treatment Options (If Linezolid Unavailable or Contraindicated)

Daptomycin is the second-line alternative for complicated UTIs caused by resistant enterococci:

• Daptomycin 6-12 mg/kg IV once daily for 5-7 days is recommended for complicated urinary tract infections due to VRE 1
• For bloodstream infections with high daptomycin MIC (3-4 mg/mL), combination with beta-lactams (penicillins, carbapenems, or cephalosporins other than cefotaxime/cefazolin) may be considered 1

Critical Clinical Considerations

This resistance pattern suggests vancomycin-resistant E. faecium (VRE), which requires specific management:

• The resistance to ampicillin, nitrofurantoin, and ciprofloxacin is characteristic of E. faecium, which has intrinsically lower susceptibility to these agents compared to E. faecalis 3, 4
• Approximately 60% of E. faecium isolates are vancomycin-resistant, making traditional first-line agents ineffective 5
• Obtain susceptibility testing for vancomycin, linezolid, and daptomycin to confirm treatment options 1

Agents to Avoid in This Case

Do not use the following agents given the documented resistance pattern:

• Nitrofurantoin is contraindicated as the organism is already documented as resistant 1
• Ampicillin/amoxicillin are ineffective given documented resistance 1
• Fluoroquinolones (ciprofloxacin) are documented as resistant and have high resistance rates (46-47%) in enterococcal UTIs 6
• Fosfomycin, while recommended for uncomplicated VRE UTIs, may have limited efficacy in complicated infections with irritative symptoms 1

Common Pitfalls to Avoid

• Do not treat asymptomatic bacteriuria: Differentiate true infection from colonization before initiating therapy, as asymptomatic bacteriuria with enterococci does not require treatment 6, 7
• Do not use inadequate dosing: Ensure linezolid is dosed at 600 mg every 12 hours, not lower doses which have shown reduced cure rates (52% vs 67%) 2
• Monitor for thrombocytopenia: Linezolid can cause thrombocytopenia, particularly with courses >14-21 days, requiring monitoring 2
• Infectious disease consultation is warranted: Management of multi-drug resistant enterococcal infections should involve specialist input given the complexity and limited treatment options 1