Should Zinnat (Cefuroxime) be discontinued in favor of a more suitable antibiotic, or should Trimethoprim/Sulfamethoxazole (TMP/SMX) be added, for a catheterized woman with urine infection caused by Providencia rettgeri and vancomycin-resistant Enterococcus faecalis?

Management of Polymicrobial Catheter-Associated UTI with Resistant Organisms

Discontinue Zinnat (cefuroxime) immediately and initiate targeted therapy based on susceptibility patterns: use ampicillin or amoxicillin for the vancomycin-resistant E. faecalis (if ampicillin-susceptible) and add trimethoprim-sulfamethoxazole for the P. rettgeri if susceptible, or consider linezolid/daptomycin for VRE plus an alternative agent for P. rettgeri based on culture sensitivities.

Why Cefuroxime Must Be Discontinued

• Cefuroxime has no activity against Enterococcus species, as enterococci are intrinsically resistant to cephalosporins 1
• P. rettgeri is already documented as resistant to most cephalosporins in this case, making cefuroxime ineffective against both pathogens 1
• Continuing ineffective therapy in a catheterized patient risks progression to pyelonephritis, bacteremia, and increased mortality 2, 3

Critical First Step: Catheter Management

• Remove or replace the urinary catheter if clinically feasible, as catheter retention is associated with treatment failure and persistent infection 2, 4
• Source control is critical for enterococcal infections and significantly impacts outcomes 3

Targeted Antibiotic Selection Algorithm

For Vancomycin-Resistant E. faecalis:

Step 1: Determine ampicillin susceptibility from culture results

• If ampicillin-susceptible: Use ampicillin (or amoxicillin orally) as the drug of choice, despite vancomycin resistance 2, 3, 5
• If ampicillin-resistant VRE:
  • Linezolid (600 mg PO/IV twice daily) is preferred for complicated UTI 2, 5, 4
  • Daptomycin (6-8 mg/kg IV daily) is an alternative for upper tract or bacteremic VRE UTI 2, 5, 4
  • Nitrofurantoin (100 mg PO four times daily) or fosfomycin (3g single dose) may be considered for uncomplicated cystitis only 5, 4

For P. rettgeri (Resistant to Penicillins, Most Cephalosporins, Nitrofurantoin):

Step 2: Review susceptibility panel for remaining options

• Trimethoprim-sulfamethoxazole (160/800 mg twice daily) is appropriate if susceptible 6, 7
• Fluoroquinolones (ciprofloxacin 500 mg twice daily or levofloxacin 750 mg daily) if susceptible, though E. faecalis is already fluoroquinolone-resistant 6
• Aminoglycosides or carbapenems may be necessary for multidrug-resistant gram-negative organisms 6, 4

Recommended Treatment Strategy

If Ampicillin-Susceptible VRE:

Combination therapy:

• Amoxicillin 500 mg PO every 8 hours for E. faecalis 3, 5
• PLUS Trimethoprim-sulfamethoxazole 160/800 mg PO twice daily for P. rettgeri (if susceptible) 6, 7
• Duration: 7-14 days for catheter-associated UTI 2, 3

If Ampicillin-Resistant VRE:

Combination therapy:

• Linezolid 600 mg PO/IV twice daily for VRE 2, 5, 4
• PLUS an agent active against P. rettgeri based on susceptibilities (TMP-SMX if susceptible, or fluoroquinolone, or parenteral carbapenem/aminoglycoside) 6, 4
• Duration: 7-14 days for uncomplicated catheter-associated UTI, 4-6 weeks if complicated by bacteremia or upper tract involvement 2, 3

Critical Pitfalls to Avoid

• Do not add TMP-SMX to cefuroxime—this leaves the VRE completely untreated and risks treatment failure 2, 5
• Do not use vancomycin for this VRE strain, as it is documented as vancomycin-resistant 2, 5
• Avoid nitrofurantoin as P. rettgeri is already resistant 5
• Do not treat asymptomatic bacteriuria in catheterized patients—only treat if symptomatic 6, 4
• Enterococcal bacteremia persisting >4 days is associated with increased mortality, so monitor closely for systemic infection 2

Monitoring Requirements

• Obtain follow-up urine cultures 48-72 hours after initiating therapy to document response 3, 4
• Monitor for clinical improvement (resolution of fever, dysuria, urgency) within 48-72 hours 3
• Consider blood cultures if fever persists or patient appears septic, as catheter-associated UTI can progress to bacteremia 2, 3
• Consider echocardiography if bacteremia persists >4 days or signs of endocarditis develop 2

Why Not Simply Add TMP-SMX to Current Therapy

• This approach would only address P. rettgeri (if susceptible) while leaving VRE completely untreated 2, 5
• Cefuroxime provides zero coverage for enterococci and is already ineffective against this P. rettgeri strain 1
• Partial treatment increases risk of persistent infection, bacteremia, and mortality 2, 3