Fosfomycin Dosing for Uncomplicated UTI
The recommended dose of fosfomycin for uncomplicated urinary tract infections in women is a single 3-gram oral dose of fosfomycin tromethamine, which should be mixed with water before ingestion and may be taken with or without food. 1, 2
Standard Dosing Regimen
A single 3-gram oral dose is the FDA-approved and guideline-recommended treatment for uncomplicated cystitis in women, providing therapeutic urinary concentrations for 24-48 hours 1, 2
The medication must be mixed with water before ingestion and should never be taken in dry form 2
This single-dose regimen is specifically endorsed by both the European Association of Urology and the American Urological Association as a first-line therapy option (Grade B evidence) 1
Clinical Efficacy and Advantages
The single-dose convenience improves adherence compared to 3-7 day regimens while achieving clinical cure rates of 99% and bacteriological eradication rates of 75-90% at 5-11 days post-treatment 1, 3
Fosfomycin maintains urinary concentrations above the EUCAST breakpoint of 32 mg/L in 100% of patients for the first 24 hours, 67.5% for 48 hours, and 30% for 72 hours 4
The drug has minimal propensity for collateral damage to intestinal flora compared to other antibiotics, making it particularly valuable in the era of antimicrobial resistance 1
Important Clinical Limitations
Fosfomycin is recommended ONLY for uncomplicated cystitis in women and should NOT be used for pyelonephritis, complicated UTIs, or routinely in men due to insufficient efficacy data for these conditions 1
For pregnant women with asymptomatic bacteriuria, fosfomycin is safe and recommended as either standard short-course treatment or single-dose administration 1
Alternative Dosing for Specific Situations
For complicated lower urinary tract infections (off-label use), a regimen of 3 grams every 48-72 hours for a total of 3 doses may be considered in patients who have failed other treatments, are infected with multidrug-resistant pathogens, or cannot tolerate first-line agents 5
This multi-dose regimen maintains urinary concentrations above 16 mg/L for approximately 161 hours (66% efficacy time over 7 days) when administered 72 hours apart 6
Common Pitfalls to Avoid
Do not use fosfomycin for pyelonephritis—fluoroquinolones and cephalosporins are preferred for upper urinary tract infections 1
Be aware that high urinary output is associated with lower urinary concentrations and reduced drug exposure, which may lead to treatment failure in some patients 4
The most common adverse effects are gastrointestinal disturbances (diarrhea, nausea, vomiting), which are typically mild and self-limiting 1, 3
Routine post-treatment urinalysis or cultures are not indicated for asymptomatic patients, but if symptoms persist or recur within 2 weeks, perform urine culture with antimicrobial susceptibility testing 1