What Is Fosfomycin? Uses, Dosage, and What You Need to Know in 2026

Fosfomycin is an antibiotic used to treat urinary tract infections (UTIs). It is sold under the brand name Monurol and is also available as a generic. What makes it unique among UTI antibiotics is its dosing: one single packet dissolved in water is the entire treatment course for most uncomplicated UTIs.

If your doctor has just prescribed fosfomycin and you want to know more about it — what it is, how it works, how to take it, and what to watch for — this guide has you covered.

What Is Fosfomycin Used For?

The FDA-approved use of oral fosfomycin is to treat uncomplicated urinary tract infections (also called acute cystitis or bladder infections) in women caused by susceptible bacteria — specifically Escherichia coli (E. coli) and Enterococcus faecalis. These two bacteria account for the vast majority of UTIs.

Common symptoms of uncomplicated UTIs that fosfomycin is used to treat include:

Burning or pain when urinating

Frequent urination or urgency (the feeling you need to urinate often, even if little comes out)

Cloudy or strong-smelling urine

Pelvic pressure or discomfort

Fosfomycin is also used off-label for complicated UTIs (using a multi-dose schedule) and in men for UTIs or prostatitis, and is considered pregnancy-safe per IDSA guidelines.

What Drug Class Is Fosfomycin?

Fosfomycin belongs to a unique antibiotic class called phosphonic acids. It is structurally unrelated to every other antibiotic on the market — including penicillins, cephalosporins, fluoroquinolones, sulfonamides, and nitrofurans. This structural uniqueness means there is generally no cross-resistance between fosfomycin and other antibiotic classes, making it particularly valuable for bacteria that have become resistant to other drugs.

How Do You Take Fosfomycin?

Empty the entire contents of one packet into 3-4 ounces (about half a cup) of cool water.

Stir until dissolved and drink it right away.

Add a small amount of water to the empty packet and drink that too — to make sure you get the full dose.

Do NOT use hot water — it can degrade the medication.

You can take fosfomycin with or without food, though taking it with food may help reduce nausea. There is only one dose — do not take a second packet unless your prescriber specifically directs you to.

What Is the Standard Fosfomycin Dosage?

Uncomplicated UTI (standard FDA-approved dose): One 3-gram (3g) sachet taken as a single oral dose

Complicated UTI (off-label): 3g every 48-72 hours, typically for 3 doses (6-21 day course), as directed by a provider

IV formulation (Contepo, hospital use only): 6g IV every 8 hours for 7 days for complicated UTIs

How Quickly Does Fosfomycin Work?

Fosfomycin begins working quickly after you take it. The drug reaches peak urine concentrations within about 2-4 hours and remains at effective levels in the urine for up to 24-48 hours after the single dose. Most patients begin feeling better within 2-3 days of taking fosfomycin. If your symptoms have not improved after 3 days, contact your prescriber.

Key Facts About Fosfomycin

Not a controlled substance: Any licensed prescriber can prescribe it; telehealth is available.

Discovered in 1969: Originally identified from Streptomyces bacteria in Spain; FDA-approved in the U.S. in 1996.

Unique mechanism: No cross-resistance with other antibiotic classes.

Generally well-tolerated: Common side effects (diarrhea, nausea, headache) are usually mild.

Pregnancy-compatible: Listed as an acceptable UTI treatment option during pregnancy in IDSA guidelines.

If you've been prescribed fosfomycin and are having trouble finding it at your pharmacy, medfinder can help you locate a pharmacy that has it. For a deeper explanation of how this drug works, read: How Does Fosfomycin Work? Mechanism of Action Explained