What Infections Does Fosfomycin Treat? A Comprehensive Guide

October 9, 2025 •

2 min read

Originally discovered in the 1960s, fosfomycin has a unique mechanism of action that makes it an effective antibiotic for certain infections. Primarily known for its role in treating uncomplicated urinary tract infections (UTIs) with a single oral dose, recent interest has expanded its use to include more serious, multi-drug resistant conditions.

Quick Summary

Fosfomycin treats uncomplicated UTIs with a single oral dose for certain bacterial strains. For multi-drug resistant infections, including systemic conditions like sepsis, intravenous fosfomycin is often used in combination with other antibiotics. Its utility covers a broad spectrum of pathogens, encompassing both Gram-positive and Gram-negative bacteria.

Key Points

Uncomplicated UTIs: Oral fosfomycin is a first-line treatment for uncomplicated bladder infections (cystitis), particularly in women, caused by susceptible E. coli and E. faecalis.
Single-Dose Convenience: A major benefit of oral fosfomycin is its single-dose regimen for uncomplicated UTIs, which leads to high, prolonged drug concentrations in the urine.
MDR Systemic Infections: Intravenous fosfomycin is used in combination therapy to treat severe, multi-drug resistant infections like sepsis, pneumonia, and bone infections.
Broad Spectrum Activity: The antibiotic is effective against a wide range of Gram-positive and Gram-negative bacteria, including resistant strains like MRSA, VRE, and ESBL-producing enterobacteriaceae.
Not for Pyelonephritis: The oral form of fosfomycin is not appropriate for treating kidney infections (pyelonephritis) due to poor concentration in kidney tissue.
Use in Combination Therapy: For serious infections, fosfomycin is typically combined with other antibiotics to prevent the rapid development of resistance.

Oral Fosfomycin: The Primary Use

Oral fosfomycin is most commonly used for uncomplicated urinary tract infections (UTIs), specifically acute cystitis. It is an effective single-dose treatment due to its high concentration in urine after administration. The main bacteria it targets for uncomplicated UTIs are Escherichia coli and Enterococcus faecalis. While multiple-dose oral regimens can be used for more complex UTIs, this is considered off-label. Oral fosfomycin is not typically recommended for kidney infections (pyelonephritis) due to insufficient concentrations in kidney tissue.

Intravenous Fosfomycin: Battling Multi-Drug Resistant Infections

Intravenous (IV) fosfomycin is used in other countries for more severe, systemic infections caused by multi-drug resistant (MDR) bacteria. It is often part of combination therapy with other antibiotics to help prevent the development of resistance. Potential uses for IV fosfomycin may include various severe infections, often caused by drug-resistant pathogens. {Link: Merck Manuals https://www.merckmanuals.com/professional/infectious-diseases/bacteria-and-antibacterial-medications/fosfomycin} provides additional details on potential uses for IV fosfomycin.

Fosfomycin for Special Populations

A single oral dose is considered safe and effective for uncomplicated cystitis during pregnancy. Oral fosfomycin has also shown effectiveness for Gram-negative UTIs in children.

The Role of Fosfomycin in the Fight Against Antimicrobial Resistance

Fosfomycin's mechanism of action gives it activity against bacteria resistant to other antibiotics, such as ESBL-producing bacteria. This makes it a valuable option, often used in combination therapy to maximize effectiveness and reduce resistance development.

Comparison of Oral vs. Intravenous Fosfomycin


Feature	Oral Fosfomycin (e.g., Monurol)	Intravenous (IV) Fosfomycin
Approved Indications (USA)	Uncomplicated urinary tract infections (cystitis) in women	Not FDA-approved; used for various systemic infections in other countries
Primary Use	Single-dose treatment for uncomplicated UTIs	Combination therapy for severe, multi-drug resistant (MDR) infections
Drug Concentrations	Reaches very high, prolonged concentrations in urine	Reaches higher, systemic concentrations in tissues and blood
Infections Treated	Lower UTIs caused by E. coli and E. faecalis	Sepsis, pneumonia, osteomyelitis, CNS infections due to MDR pathogens
Risk of Resistance	Lower risk due to short duration, but resistance can develop with increased use	Higher risk of resistance developing during prolonged treatment, necessitates combination therapy
Availability	Widely available as a powder for oral solution	Restricted availability in some regions, requires hospital administration

Conclusion

Fosfomycin is a valuable antibiotic for uncomplicated UTIs with its single oral dose. It is effective against key urinary pathogens like E. coli. For serious, multi-drug resistant infections, IV fosfomycin is used in combination therapy. Its unique mechanism and low cross-resistance potential make it important in the fight against antibiotic resistance, requiring careful use to maintain its effectiveness. Strategic use of fosfomycin is vital as antimicrobial resistance increases globally.

This article is for informational purposes only and is not a substitute for professional medical advice. Always consult with a healthcare provider for diagnosis and treatment.

Frequently Asked Questions

Fosfomycin is primarily used to treat uncomplicated urinary tract infections (UTIs) or acute cystitis caused by susceptible bacteria like Escherichia coli and Enterococcus faecalis.

For uncomplicated UTIs, fosfomycin is typically prescribed as a single, oral dose. For more complicated or systemic infections, a multiple-dose regimen, sometimes via IV, is used.

Yes, fosfomycin can be used for complicated UTIs, though it is considered an off-label use for the oral form. Treatment typically involves a multiple-dose regimen over several days.

Yes, fosfomycin has shown activity against MDR bacteria, including ESBL-producing strains, MRSA, and VRE. For these serious infections, it is often used intravenously and in combination with other antibiotics.

Oral fosfomycin is not recommended for treating pyelonephritis because it does not achieve high enough concentrations in kidney tissue. Intravenous formulations may be used in certain severe cases, but caution is advised.

Oral fosfomycin is mainly used for UTIs and achieves high urine concentrations. Intravenous fosfomycin is used for more severe systemic infections and achieves higher, more widely distributed concentrations throughout the body.

Fosfomycin is generally considered safe for treating uncomplicated cystitis in pregnant women.