What is the recommended dosage of Fosfomycin for uncomplicated urinary tract infections?

Fosfomycin Dosage for Uncomplicated Urinary Tract Infections

For uncomplicated urinary tract infections (acute cystitis) in women, the recommended dosage is a single 3-gram oral dose of fosfomycin tromethamine, mixed with water before ingestion. 1

Standard Dosing Regimen

• Single-dose therapy: One 3-gram sachet of fosfomycin tromethamine granules dissolved in water is the FDA-approved dosage for women 18 years and older with uncomplicated UTI 1
• The medication may be taken with or without food, but must never be taken in dry form—always mix with water before ingesting 1
• This single dose provides therapeutic urinary concentrations for 24-48 hours 2

Clinical Efficacy and Positioning

• First-line therapy status: Multiple guidelines, including the American Urological Association, European Association of Urology, and Infectious Diseases Society of America, recommend fosfomycin as a first-line treatment option for uncomplicated cystitis in women 3, 2
• Clinical cure rates are comparable to 3-day trimethoprim-sulfamethoxazole and 5-day nitrofurantoin regimens, though bacteriological efficacy may be slightly lower 3, 2
• The single-dose convenience significantly improves adherence compared to multi-day regimens 2
• Fosfomycin has minimal propensity for collateral damage to intestinal flora and maintains low resistance rates 3, 2

Extended Dosing for Specific Situations

For complicated lower UTI or treatment failures: When patients have failed other agents, are infected with multidrug-resistant pathogens, or cannot tolerate first-line treatments, an extended regimen of 3 grams every 48-72 hours for a total of 3 doses can be used off-label 4

For VRE-associated uncomplicated UTI: The same single 3-gram oral dose is recommended 3

Important Limitations and Contraindications

• Do NOT use for pyelonephritis: Fosfomycin is not recommended for upper urinary tract infections due to insufficient efficacy data 2
• Do NOT use for complicated UTIs: Oral fosfomycin should be reserved for uncomplicated cystitis only 2
• Limited data in men: The European guidelines do not recommend fosfomycin for routine use in men with UTIs due to limited clinical efficacy data 2

Special Populations

• Pregnancy: Fosfomycin is safe in pregnancy and recommended for asymptomatic bacteriuria in pregnant women using the standard single 3-gram dose 2
• Single-dose fosfomycin showed similar bacteriological efficacy to 5-7 day courses of other antibiotics in pregnant women 5

Adverse Effects

• Most common side effects are gastrointestinal: diarrhea, nausea, and vomiting 2
• Adverse events are generally mild and self-limited 6, 5
• Initial reports show higher rates of side effects at day 4 compared to multi-day regimens, but rates equalize by day 9 6

Follow-Up Considerations

• Routine post-treatment urinalysis or urine cultures are not indicated for asymptomatic patients 2
• If symptoms do not resolve by end of treatment or recur within 2 weeks, perform urine culture and antimicrobial susceptibility testing 2