What is the recommended dosing and duration of Fosfomycin (Fosfomycin) for the treatment of uncomplicated urinary tract infections (UTIs)?

Fosfomycin Dosing and Duration for Uncomplicated UTIs

For uncomplicated urinary tract infections (UTIs) in women, a single 3-gram oral dose of fosfomycin tromethamine is the recommended regimen. 1, 2

Standard Dosing for Uncomplicated UTIs

• Fosfomycin tromethamine is administered as a single 3-gram sachet dissolved in water for uncomplicated UTIs in women 2
• The medication can be taken with or without food 2
• This single-dose regimen is specifically recommended for women with uncomplicated cystitis 1
• The single-dose administration provides therapeutic urinary concentrations for 24-48 hours, which is sufficient to inhibit most urinary pathogens 3

Clinical Efficacy

• Single-dose fosfomycin achieves high clinical recovery rates (88.9%) and bacteriological eradication rates (94.9%) in uncomplicated UTIs 4
• While bacterial efficacy of fosfomycin is somewhat lower than some other first-line agents, clinical efficacy is comparable 1
• The convenience of a single-dose regimen, activity against resistant gram-negative rods, and minimal propensity for collateral damage make fosfomycin a useful choice 1

Special Considerations

• Fosfomycin is particularly active against common uropathogens including Escherichia coli, Citrobacter, Enterobacter, Klebsiella, Serratia and Enterococcus species 3
• For vancomycin-resistant Enterococcus (VRE) causing uncomplicated UTIs, the same single 3-gram oral dose is recommended 1
• Peak urinary concentrations occur within 4 hours of administration and remain high (>128 mg/L) for 24-48 hours 3

Alternative Regimens

• For complicated or multidrug-resistant UTIs, while not FDA-approved for this indication, some evidence suggests fosfomycin may be effective 5
• Some pharmacokinetic studies suggest that for longer treatment periods (such as 7 days of coverage), two 3-gram doses administered 72 hours apart may be optimal 6
• However, for standard uncomplicated UTIs in women, the single-dose regimen remains the standard of care 1

Important Caveats

• Fosfomycin should always be mixed with water before ingestion - never take the medication in its dry form 2
• If symptoms do not resolve by the end of treatment or recur within 2 weeks, urine culture and antimicrobial susceptibility testing should be performed 1
• Gastrointestinal side effects (nausea, diarrhea) are the most common adverse reactions but are typically mild, transient, and self-limiting 3
• Routine post-treatment urinalysis or urine cultures are not indicated for asymptomatic patients 1

Comparison with Other First-Line Agents

• Fosfomycin has comparable clinical efficacy to nitrofurantoin but with the advantage of single-dose administration versus nitrofurantoin's 5-day regimen 7
• The European Association of Urology lists fosfomycin trometamol as a first-line treatment option for uncomplicated cystitis in women 1
• There appears to be little cross-resistance between fosfomycin and other antibacterial agents due to its unique chemical structure and mechanism of action 3