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Overview: Fosfomycin is an antibiotic used to treat bladder infections caused by certain bacteria. Common side effects include diarrhea, nausea, or headache. Tell your health care provider right away if you get severe diarrhea, even several months after stopping the medicine.

Uses

What is fosfomycin used for?

Fosfomycin is an antibiotic that is commonly used to treat bladder infections caused by certain bacteria.

Fosfomycin may also be used for other conditions as determined by your health care provider.

Fosfomycin may not be the right drug for infections other than what is stated above. Some bacteria may have developed resistance to fosfomycin, which will make it not work as well.

How does fosfomycin work (mechanism of action)?

Fosfomycin kills certain bacteria by preventing them from creating their cell wall. Without a cell wall, bacteria cannot survive and grow.

How is fosfomycin supplied (dosage forms)?

Brands and other names

  • Monurol

Dosage forms and strengths

  • 3 g packets of granules for oral solution

How should I store fosfomycin?

Fosfomycin should be stored at room temperature, between 68 F and 77 F (20 C and 25 C). It can be exposed to temperatures between 59 F and 86 F (15 C and 30 C) for shorter periods of time, such as when transporting it. Store in a cool, dry place.

Side Effects

What are the most common side effects of fosfomycin?

The most common side effects of fosfomycin are listed below. Tell your health care provider if you have any of these side effects that bother you.

  • Diarrhea 
  • Swollen, itchy, or sore vaginal area (vaginitis)
  • Nausea
  • Headache

There may be other side effects of fosfomycin that are not listed here. Contact your health care provider if you think you are having a side effect of a medicine. In the U.S., you can report side effects to the FDA at www.fda.gov/medwatch or by calling 800-FDA-1088 (800-332-1088). In Canada, you can report side effects to Health Canada at www.health.gc.ca/medeffect or by calling 866-234-2345.

What are the serious side effects of fosfomycin?

While less common, the most serious side effects of fosfomycin are described below, along with what to do if they happen.

Severe Allergic Reactions. Fosfomycin may cause allergic reactions, which can be serious. Stop taking fosfomycin and get help right away if you have any of the following symptoms of a serious allergic reaction.

  • Breathing problems or wheezing
  • Racing heart
  • Fever or general ill feeling
  • Swollen lymph nodes
  • Swelling of the face, lips, mouth, tongue, or throat
  • Trouble swallowing or throat tightness
  • Itching, skin rash, or pale red bumps on the skin called hives
  • Nausea or vomiting
  • Dizziness, feeling lightheaded, or fainting
  • Stomach cramps
  • Joint pain

Antibiotic-Associated Diarrhea. An overgrowth of germs called Clostridioides difficile (C. diff) can happen in your gut with many types of antibiotics, including fosfomycin. This can cause a condition known as antibiotic-associated diarrhea and can happen even two months or more after stopping the antibiotic. Call your health care provider right away if you have any of the following symptoms of this condition.

  • Watery diarrhea
  • Diarrhea that does not go away
  • Blood in your stool (poop)
  • Severe stomach cramps
  • Fever that starts after you start or finish the medicine

Warnings & Precautions

Who should not use fosfomycin?

Allergies to Ingredients. People who are allergic to any of the following should not take fosfomycin.

  • Fosfomycin
  • Monurol
  • Any of the ingredients in the specific product dispensed

Your pharmacist can tell you all of the ingredients in the specific fosfomycin products they stock.

What should I know about fosfomycin before using it?

Do not take fosfomycin unless it has been prescribed to you by a health care provider. Take it as prescribed.

Do not share fosfomycin with other people, even if they have the same condition as you. It may harm them.

Keep fosfomycin out of the reach of children.

Do not take fosfomycin granules without dissolving them in about 3-4 oz (about half a cup) of water. Do not use hot water to dissolve fosfomycin. Take the dose right after dissolving it in water. Ask your pharmacist if you have any questions about how to prepare your dose of fosfomycin.

Tell your health care provider if your bladder infection symptoms come back after getting better or if your symptoms do not improve within two to three days of taking fosfomycin.

What should I tell my health care provider before using fosfomycin?

Tell your health care provider about all of your health conditions and any prescription or over-the-counter (OTC) medicines, vitamins/minerals, herbal products, and other supplements you are using. This will help them determine if fosfomycin is right for you.

In particular, make sure that you discuss any of the following.

Other Medicines and Supplements. Fosfomycin may interact with other medicines and supplements. Before taking fosfomycin, tell your health care provider about any prescription or over-the-counter (OTC) medicines, vitamins/minerals, herbal products, and other supplements you are using. See the Interactions section for more details.

Pregnancy. It is not known if or how fosfomycin could affect pregnancy or harm an unborn baby. Tell your health care provider if you are pregnant or plan to become pregnant.

Breastfeeding. It is not known if fosfomycin passes into breast milk. Tell your health care provider if you are breastfeeding or plan to breastfeed. Your health care provider will let you know if you should stop breastfeeding or not take fosfomycin.

Interactions

Does fosfomycin interact with foods or drinks?

There are no known interactions between fosfomycin and foods or drinks.

It is unknown if drinking alcohol will affect fosfomycin, but heavy drinking can slow your immune response and make it harder for your body to fight infection. 

Does fosfomycin interact with other medicines (drug interactions)?

Always tell your health care provider about any prescription or over-the-counter (OTC) medicines, vitamins/minerals, herbal products, and other supplements you are using.

In particular, make sure that you discuss if you are taking any medicine that can affect how quickly things move through your stomach and intestines, such as metoclopramide (Reglan and others), before taking fosfomycin.

This may not be a complete list of medicines that can interact with fosfomycin. Always check with your health care provider.

Does interact with other drugs you are taking?

Enter your medication into the WebMD interaction checker

Overdose/Missed Dose

What should I do if I accidentally use too much fosfomycin?

If you or someone else has used too much fosfomycin, get medical help right away, call 911, or contact a Poison Control center at 800-222-1222.

What should I do if I miss a dose of fosfomycin?

Fosfomycin is a single-dose medicine. One dose of fosfomycin is usually considered a full treatment.