Fosfomycin: Uses, Side Effects, Dosages, Contra-indications, Warnings, Interactions & More

By Sarah Malka, MD
Medically reviewed
July 2, 2021

Aside from doctors, most people don’t know much about different antibiotics. So it’s totally natural if you’ve never heard of fosfomycin.

But if you’ve ever had a UTI, you may have taken this antibiotic and not realized it because the doctor simply said, “Here’s a prescription for an antibiotic.”

Sold under the brand name Monurol, fosfomycin is used to treat urinary tract infections and other bladder infections.

It is considered a broad-spectrum drug, meaning it acts against a wide variety of disease-causing bacteria in your body. 

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What Is Fosfomycin?

Fosfomycin (the active agent in the chemical compound fosfomycin tromethamine or fosfomycin trometamol) is an antibiotic or antibacterial drug approved by the FDA for the treatment of urinary tract infections and cystitis (bladder infections).

It is taken orally as a single-dose powder packet dissolved in a glass of water. Fosfomycin is safe and effective for most adults.  

What Is It Used For?

Fosfomycin is a bactericidal drug. That means it kills bacteria like escherichia coli (E. coli) that can multiply and spread in your urinary tract, causing infection and the resulting pain and inflammation.

The drug works by preventing bacteria from being able to form cell walls so it can’t multiply.

What conditions can it treat?

Fosfomycin is FDA-approved to treat uncomplicated UTIs. Let’s break this down. 

Your urinary system is composed of your urethra, bladder, and kidneys.

Any of these areas can be affected by bacterial pathogens like E. coli, enterobacteriaceae such as enterobacter, enterococcus faecalis (E. faecalis) and other enterococci, staphylococcus aureus, or klebsiella pneumoniae. 

A lower tract UTI, also known as a bladder infection, is the most common and easiest type of UTI to treat.

Symptoms include a burning sensation when you urinate, a frequent need to urinate, blood in the urine, and abdominal pain. 

An upper tract UTI tends to occur as the result of an untreated lower tract UTI that spreads upward to the kidneys. This is called a kidney infection (pyelonephritis) and can be serious, potentially requiring a hospital visit to avoid permanent organ damage.

Signs you might have a kidney infection include fever, lower back or side pain, chills, and nausea. 

Uncomplicated UTIs are ones in which the person’s urinary tract is normal and they have no history of health problems.

On the other hand, complicated UTIs occur when someone has a condition or anatomical abnormality (such as kidney stones, a medical device, or an enlarged prostate) blocking the urinary tract.

In addition to being used to treat uncomplicated UTIs, fosfomycin is currently being studied in the US for its potential ability to treat multidrug-resistant infections.

Here’s what that means: The bacteria that cause infections like UTIs have the ability to “learn” about the drugs we use against them and use enzymes to protect themselves.

That’s great for them but not so great for you, because it means the antibiotic your doctor prescribes may not kill those bacteria. This is known as antibiotic resistance or antimicrobial resistance. 

But scientists think that fosfomycin might be able to beat multidrug-resistant infections because of its ability to kill several different families of bacteria, including ESBL-producing gram-positive bacteria and gram-negative bacteria.

It’s not approved for this use in the US, but in Europe, it is prescribed in intravenous (IV) form for this purpose. 

Can You Get Fosfomycin Online?

You need a doctor’s prescription to get this antibiotic, but you don’t necessarily need to see a doctor in person. K Health offers affordable outpatient treatment for all kinds of medical conditions, including UTIs, directly through your phone.

Chat with a doctor instantly to discuss your symptoms and whether an antibiotic like fosfomycin, nitrofurantoin, or carbapenem might be right for you. If so, you can get a prescription and either pick up the medication at your local pharmacy or have it delivered.

Chat with a doctor and get an antibiotic prescription for just $23

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What Are Common Dosages of Fosfomycin?

For adults, fosfomycin is generally available as a single-dose sachet of three grams of medication. It has a high bioavailability, so there’s typically no need to take it more than once. However, in certain instances (like if your UTI won’t go away), your doctor may choose a different dosing strategy. 

Side Effects

The vast majority of adults take fosfomycin without adverse effects. The main side effects include:

Contact your healthcare provider if any of the above becomes severe or if you experience any of the below more serious side effects:

  • Fever
  • Joint pain
  • Swelling of the throat area
  • Yellowing skin or eyes (jaundice)

How to Take Fosfomycin

Fosfomycin is taken in powder form. You mix the sachet into three to four ounces of water, stir to dissolve, and drink it immediately. (Don’t mix with hot water, as this can degrade the quality of the medication.)

Unlike most other antibiotics, fosfomycin is a one-and-done dose, so you don’t have to worry about remembering to take pills on a schedule. After you take it, your symptoms should subside within a few days. 

Contraindications

Fosfomycin is very safe for the treatment of uncomplicated urinary tract infections, but it’s not right for everyone. Be sure to tell your doctor if you:

  • Are pregnant or breastfeeding.
  • Take any medications. In particular, metoclopramide (Reglan) and cisapride (Propulsid) may make fosfomycin less effective. Also inform your healthcare provider about any vitamins or supplements you take.
  • Have been allergic to an antibiotic before or have a history of medication allergies or hypersensitivity.
  • Have glucose-6-phosphate dehydrogenase (G6PD) deficiency. People with this genetic condition are more susceptible to anemia, and sometimes their bodies can’t tolerate antibiotics.

Warnings

Fosfomycin shouldn’t cause any major reactions in your body, so if you have severe nausea, vomiting, fever, or muscle pain, call your doctor ASAP. 

Your UTI should go away within a few days, but if your symptoms persist, let your provider know. Sometimes the body doesn’t respond to an antibiotic.

In this case, the “bad” bacteria in your body may have developed something called fosfomycin resistance, meaning they’ve figured out how to evade this antibiotic and survive. Antibiotic resistance is unfortunately quite common—at least 2.8 million Americans get an antibiotic-resistant infection every year.

It’s an issue that microbiologists continue to study. All you need to know is your doctor will likely collect a urine culture to identify the type(s) of bacteria in your urinary tract and then write another prescription for you.

How K Health Can Help

K Health provides a simple, accessible option for prescription treatment. Chat with a doctor on your phone to determine whether you need a prescription. Your doctor will then prescribe you medication, which can be picked up at a local pharmacy or shipped discreetly directly to you. 

Frequently Asked Questions

How does fosfomycin work?
Fosfomycin is an antibiotic or antibacterial drug. It works by killing bacteria like E. coli that multiply and spread in your urinary tract, causing a UTI.
What type of antibiotic is fosfomycin?
Fosfomycin is a broad-spectrum antibiotic, meaning it works against a variety of infection-causing bacteria. It is used for the treatment of uncomplicated urinary tract infections and cystitis.
Is fosfomycin a strong antibiotic?
It’s taken as a single dose, so you could say it’s pretty strong! Unlike most antibiotics, which require a multi-day regimen of pills, fosfomycin only needs to be taken one time in a glass of water.
How quickly does fosfomycin work?
After taking fosfomycin, your UTI symptoms should subside within a few days. If they persist longer than that, talk to your doctor.
K Health articles are all written and reviewed by MDs, PhDs, NPs, or PharmDs and are for informational purposes only. This information does not constitute and should not be relied on for professional medical advice. Always talk to your doctor about the risks and benefits of any treatment.

Sarah Malka, MD

Dr. Sarah Malka is a board certified emergency medicine physician with K Health. She completed her residency at Harvard Medical School.