Fosfomycin Dosing for Uncomplicated UTI
For uncomplicated urinary tract infections (acute cystitis) in women, prescribe a single 3-gram oral dose of fosfomycin tromethamine. 1
Standard Dosing Regimen
- Single 3-gram oral dose is the FDA-approved and guideline-recommended treatment for uncomplicated UTI in women 1, 2, 3
- Mix the entire contents of one sachet in 3-4 ounces (½ cup) of water and drink immediately; do not use hot water or take in dry form 1
- Can be taken with or without food 1
- Provides therapeutic urinary concentrations for 24-48 hours after administration 3, 4
Clinical Efficacy
- Bacteriological eradication rates of 75-90% at 5-11 days post-treatment, with 62-93% sustained eradication at 4-6 weeks 4
- Clinical cure rates comparable to nitrofurantoin (5 days) and trimethoprim-sulfamethoxazole (3 days), with the advantage of single-dose convenience 5, 2, 3
- Particularly effective against E. coli, which causes >75% of uncomplicated cystitis 2, 4
- Maintains low resistance rates in community settings, making it a valuable first-line option 6
Important Limitations and Contraindications
Do NOT use fosfomycin for:
- Pyelonephritis - insufficient efficacy data; use fluoroquinolones (5-7 days) or TMP-SMZ (14 days) instead 3, 2
- Complicated UTIs - limited evidence for efficacy, though some retrospective data suggests potential benefit 7, 3
- Routine use in men - limited clinical efficacy data in male patients 3
Special Populations
- Pregnant women with asymptomatic bacteriuria: Single-dose fosfomycin is recommended as an alternative to standard short-course therapy 2, 3
- VRE-associated uncomplicated UTI: Same single 3-gram dose is effective 2, 3
Follow-Up Considerations
- Routine post-treatment urine cultures are not indicated for asymptomatic patients 2
- Obtain urine culture and susceptibility testing if symptoms persist beyond treatment completion or recur within 2-4 weeks 2, 3
Comparative Context
Fosfomycin ranks among three first-line therapies recommended by major guidelines (AUA, IDSA/ESCMID, EAU) alongside nitrofurantoin (5 days) and TMP-SMZ (3 days) 2, 3. While bacterial efficacy may be somewhat lower than other agents, clinical efficacy is comparable, and the single-dose regimen offers superior convenience and minimal collateral damage to intestinal flora 3, 4.