What Does Fosfomycin Treat?
Fosfomycin is indicated specifically for uncomplicated urinary tract infections (acute cystitis) in women, caused by susceptible strains of Escherichia coli and Enterococcus faecalis. 1
Primary Indication: Uncomplicated Cystitis in Women
Fosfomycin tromethamine is FDA-approved and recommended as first-line treatment for uncomplicated cystitis in women only, administered as a single 3-gram oral dose 2, 1. The 2024 European Association of Urology guidelines explicitly state this is the only population for which oral fosfomycin is recommended 2.
Key Clinical Parameters:
- Patient population: Non-pregnant women with no anatomic or functional urinary tract abnormalities and no comorbidities
- Symptoms: Dysuria, frequency, urgency without vaginal discharge
- Dosing: Single 3-gram oral dose
- Duration: One day only
Additional Approved Uses
Asymptomatic Bacteriuria in Pregnancy
Fosfomycin can be used as single-dose treatment for asymptomatic bacteriuria in pregnant women before urological procedures that breach the mucosa 2. This represents a weak recommendation based on older evidence, but remains guideline-supported.
Intravenous Formulation (Where Available)
In countries where IV fosfomycin is available, it may be used for:
- Complicated UTIs and acute pyelonephritis (recently FDA-approved in the US) 3
- ESBL-producing, non-bacteremic cUTI/AP in hemodynamically stable patients 3
However, the 2024 JAMA guidelines note there is insufficient evidence to provide clear recommendations for fosfomycin duration in febrile UTI or pyelonephritis 4.
Critical Limitations and Contraindications
Fosfomycin is NOT indicated for:
- Pyelonephritis (upper UTI) when using oral formulation 1
- Perinephric abscess 1
- Complicated UTIs (oral formulation)
- Men with cystitis (not included in FDA approval or EAU first-line recommendations) 2, 1
- Bacteremia from urinary source (FOREST trial showed it did not meet noninferiority and had more adverse effects) 3
Important Caveat:
If bacteriuria persists or reappears after fosfomycin treatment, other therapeutic agents must be selected 1. The drug should not be repeated for treatment failures.
Resistance Considerations
While fosfomycin maintains excellent activity against E. coli (96.4% susceptibility in recent European surveillance) 5, contemporary resistance rates to trimethoprim-sulfamethoxazole in many regions limit its utility as first-line treatment 4. Fosfomycin's advantage is its lack of cross-resistance with beta-lactams and aminoglycosides 1.
Emerging but Unproven Uses
Research suggests potential activity in soft tissue infections 6 and against multidrug-resistant gram-negative bacteria 7, 8, but these remain investigational and should not guide current clinical practice. Fosfomycin monotherapy should be avoided outside approved indications due to rapid resistance development 8.