Can I prescribe fosfomycin for a patient with an indwelling Foley catheter who has a symptomatic urinary tract infection?

Fosfomycin for Symptomatic UTI with Indwelling Foley Catheter

You should not prescribe fosfomycin for a patient with an indwelling Foley catheter who has a symptomatic urinary tract infection. Fosfomycin is FDA-approved only for uncomplicated acute cystitis in women and is explicitly not indicated for complicated infections 1. Catheter-associated UTIs (CAUTIs) are by definition complicated infections that require different therapeutic approaches.

Why Fosfomycin Is Not Appropriate

FDA Labeling Restrictions

• Fosfomycin tromethamine is indicated only for uncomplicated urinary tract infections (acute cystitis) in women caused by susceptible E. coli and Enterococcus faecalis 1
• The FDA label explicitly states fosfomycin is not indicated for pyelonephritis or perinephric abscess, and any catheter-associated infection falls into the complicated UTI category 1

Guideline Recommendations for CAUTI Management

• The presence of an indwelling catheter automatically classifies the infection as complicated, requiring broader antimicrobial coverage and consideration of catheter management 2
• Standard fosfomycin dosing (single 3g dose) was designed for uncomplicated cystitis, not for the biofilm-associated infections that occur with indwelling catheters 1, 3

Appropriate Management of Symptomatic CAUTI

First: Confirm True Infection vs. Asymptomatic Bacteriuria

Before treating, verify the patient has true symptomatic infection 2, 4:

• Fever ≥38°C (100.4°F) without alternative source 4, 5
• New suprapubic pain or costovertebral angle tenderness 4, 5
• Rigors, hypotension, or sepsis criteria 4, 5
• Acute delirium or altered mental status (especially in elderly) 4, 5

Critical pitfall: Cloudy urine, pyuria, positive urine culture, or foul-smelling urine alone do not indicate infection in catheterized patients and should not trigger treatment 4, 5

Catheter Management

• Replace the catheter before obtaining urine culture if it has been in place >2 weeks, as this improves diagnostic accuracy and may clear bacteriuria in ~40% of cases 4, 5
• Obtain culture from freshly collected urine through the new catheter while temporarily occluded; never sample from drainage bags or extension tubing 6
• Remove the catheter entirely if no longer medically necessary, as this is the most effective intervention 2

Antimicrobial Selection

For confirmed symptomatic CAUTI, choose antibiotics based on:

• Local resistance patterns and prior culture data
• Severity of illness (oral vs. IV therapy)
• Renal function and drug penetration into urine
• Not fosfomycin, which lacks evidence and approval for this indication 1

Limited Research Data on Fosfomycin for CAUTI

Small Retrospective Studies Show Mixed Results

• One multicenter retrospective study of 35 CAUTI patients used an off-label extended regimen (3g daily × 2 days, then 3g every 48h × 2 weeks) and reported 85.7% remained infection-free during follow-up 7
• However, this required multiple doses over weeks—not the FDA-approved single-dose regimen—and 11.6% failed treatment entirely 7
• Another retrospective study of 57 patients with complicated/MDR UTIs (including some with catheters) showed 96.4% clinical success, but only 49.1% were clinically evaluable due to study limitations 8

Why This Research Cannot Override FDA Labeling

• These studies used off-label dosing regimens not supported by pharmacokinetic/pharmacodynamic data for catheter-associated infections 7, 8
• The single-dose regimen achieves high urinary concentrations for 24-48 hours, which may be insufficient for biofilm-eradicated infections requiring prolonged exposure 3, 9
• No randomized controlled trials compare fosfomycin to standard CAUTI therapies 7, 8

When Fosfomycin Is Appropriate

Fosfomycin remains an excellent choice for:

• Uncomplicated acute cystitis in women without catheters, particularly when caused by MDR E. coli 1, 10
• Single-dose therapy ensures compliance and minimizes resistance selection 3, 10
• Pregnancy category B makes it suitable for pregnant women with uncomplicated UTI 3

Summary Algorithm

Does the patient have an indwelling catheter?

• Yes → Fosfomycin is not appropriate; manage as CAUTI (see above) 1, 2
• No → Proceed to next question

Is this uncomplicated acute cystitis in a woman?

• Yes → Fosfomycin 3g single dose is appropriate 1, 10
• No (pyelonephritis, male patient, recurrent infection) → Choose alternative agent 1

Common pitfall: Do not treat asymptomatic bacteriuria in catheterized patients regardless of diabetes, cloudiness, or positive culture—this increases resistance without improving outcomes 2, 4, 5