How to prescribe Fosfomycin (Fosfomycin) for an uncomplicated urinary tract infection (UTI)?

Fosfomycin Prescription for Uncomplicated UTI

For uncomplicated urinary tract infections in women, prescribe fosfomycin tromethamine as a single 3g sachet dissolved in 3-4 ounces (1/2 cup) of cold water, taken immediately after mixing. 1

Indication and Patient Selection

Fosfomycin is indicated for:

• Women with uncomplicated urinary tract infections (acute cystitis)
• Infections caused by susceptible strains of E. coli and Enterococcus faecalis 1

Fosfomycin is NOT indicated for:

• Pyelonephritis or perinephric abscess 1
• Men with UTIs (not FDA approved)
• Complicated UTIs

Administration Instructions

1. Pour the entire contents of one 3g sachet into 3-4 ounces (1/2 cup) of cold water
2. Stir to dissolve completely (do NOT use hot water)
3. Drink immediately after mixing
4. Can be taken with or without food 1

Clinical Efficacy

Fosfomycin is recommended as a first-line agent for uncomplicated UTIs by multiple guidelines:

• IDSA/European Society for Microbiology and Infectious Diseases guidelines recommend it as a single 3g dose 2
• American College of Physicians endorses single-dose fosfomycin as an effective treatment option 2

Fosfomycin achieves:

• High urinary concentrations (>128 mg/L) for 24-48 hours after a single dose 3
• Bacteriological eradication rates of 75-90% at 5-11 days post-treatment 3
• Clinical cure rates of approximately 88.9% 4

Advantages and Limitations

Advantages:

• Single-dose administration improves compliance 5
• Effective against ESBL-producing bacteria 5
• Low rates of cross-resistance with other antibiotics 3
• Minimal disruption to gut microbiome compared to longer courses of other antibiotics

Limitations:

• Slightly lower efficacy than some other recommended agents 2
• Not appropriate if early pyelonephritis is suspected 2
• Baseline heteroresistance may affect treatment response 6

Alternative Options

If fosfomycin is unavailable or contraindicated, consider:

• Nitrofurantoin monohydrate/macrocrystals 100 mg twice daily for 5 days
• Trimethoprim-sulfamethoxazole 160/800 mg (one DS tablet) twice daily for 3 days (if local resistance <20%)
• Fluoroquinolones should be reserved for cases where other options cannot be used 2, 5

Monitoring and Follow-up

• If symptoms persist or recur after treatment, obtain a urine culture and select an alternative agent 1
• No routine follow-up urine culture is needed if symptoms resolve
• Patients with heart failure risk should be monitored, as 8.6% developed heart failure in the FOREST trial 5

Common Side Effects

Fosfomycin is generally well-tolerated with:

• Primarily gastrointestinal side effects (diarrhea, nausea) in approximately 4.3% of patients 4
• Side effects are typically transient, mild, and self-limiting 3

Key Prescribing Pitfalls to Avoid

1. Do not prescribe for pyelonephritis or complicated UTIs
2. Do not instruct patients to take the powder dry - it must be dissolved in water
3. Do not use hot water for dissolution
4. Do not prescribe multiple doses for uncomplicated UTIs - a single dose is the standard regimen
5. Do not use for UTIs in men (not FDA approved for this indication)