What is the recommended treatment and dosage of fosfomycin for urinary tract infections (UTIs)?

Fosfomycin Treatment for Urinary Tract Infections

For uncomplicated urinary tract infections (UTIs) in women, fosfomycin tromethamine is recommended as a single 3-gram oral dose, which provides therapeutic urinary concentrations for 24-48 hours. 1, 2

Standard Dosing Recommendations

• Fosfomycin tromethamine is administered as a single 3-gram sachet mixed with water for women 18 years and older with uncomplicated UTIs (acute cystitis) 2
• The single-dose regimen provides high urinary concentrations (>128 mg/L) that remain effective for 24-48 hours, which is sufficient to inhibit most urinary tract pathogens 3
• Fosfomycin may be taken with or without food, but should always be mixed with water before ingestion 2

Clinical Efficacy and Indications

• Fosfomycin is recognized as a first-line treatment option for uncomplicated cystitis in women by both European and American Urological Associations with strong recommendation (Grade B evidence) 1
• Clinical recovery rates and bacteriological eradication rates of 75-90% are typically achieved 5-11 days after therapy 3
• While bacterial efficacy may be somewhat lower than some other first-line agents, clinical efficacy is comparable, with the convenience of single-dose administration 1
• Fosfomycin is particularly effective against common uropathogens including Escherichia coli and Enterococcus species 4

Special Considerations

• Fosfomycin is specifically FDA approved for uncomplicated UTIs in women and should not be used for pyelonephritis, complicated UTIs, or routinely in men due to limited efficacy data 1
• For pregnant women with asymptomatic bacteriuria, fosfomycin is recommended as a safe single-dose treatment option 1
• No dosage adjustments are required for elderly patients or those with renal or hepatic impairment 4

Antimicrobial Spectrum and Resistance

• Fosfomycin demonstrates broad-spectrum activity against ESBL-producing, AmpC-producing, and multidrug-resistant (MDR) E. coli 4
• It is FDA approved for UTIs caused by E. coli and Enterococcus faecalis, including vancomycin-resistant Enterococcus (VRE) 5, 1
• Resistance to fosfomycin in E. coli is rare (<1%), and there is little cross-resistance with other antibacterial agents due to its unique mechanism of action 4

Adverse Effects

• Fosfomycin is generally well-tolerated with a low incidence of adverse events 3
• The most common side effects are gastrointestinal symptoms (diarrhea, nausea, vomiting) that are typically transient, mild, and self-limiting 1, 3

Clinical Pearls

• Routine post-treatment urinalysis or urine cultures are not indicated for asymptomatic patients 1
• 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
• The single-dose administration regimen offers improved patient compliance compared to multi-day regimens 4
• Fosfomycin has minimal propensity for collateral damage to intestinal flora compared to other antibiotics, making it a favorable choice for UTI treatment 1