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What You Need To Know About Flagyl (Metronidazole)

Flagyl Is An Antibiotic That Is Used To Treat Infections


Updated May 27, 2014

Written or reviewed by a board-certified physician. See About.com's Medical Review Board.

pills spilling out from a bottle
Daryl Solomon/Photographer's Choice RF/Getty Images
Generic name: Metronidazole
Other brand name: Protostat

What Is Flagyl?

Flagyl is an antibacterial drug. It is used to kill any bacteria in the body that are causing infection.

How Is It Taken?

Flagyl is taken orally in tablet form. In order for Flagyl to effectively kill harmful bacteria, it is important to maintain a constant level of Flagyl in the blood. Therefore, it must be taken at regular intervals without missing any doses. Take Flagyl with 8 ounces of water.

Flagyl can be taken by itself, or it can be taken with meals. If dry mouth becomes bothersome, try chewing gum, or sucking on hard candy or ice chips.

Why Is It Prescribed?

Flagyl is used to fight or to prevent a bacterial infection. It is used to treat a wide variety of infections, including those in the abdomen, bones, joints, nervous system, respiratory tract, and skin, as well as vaginal and intestinal infections.

What Do I Do If I Miss A Dose?

If you miss a dose, take it as soon as you remember. If your next dose should be taken soon, just take that dose. Don't double up or take more than one dose of Flagyl at a time.

Who Should Not Take Flagyl?

People with an allergy or sensitivity to metronidazole should also not take Flagyl. Flagyl should be used under the close supervision of a physician by anyone who has liver disease.

Yeast infections may worsen while taking Flagyl.

If I Start To Feel Better, Can I Stop Taking Flagyl?

NO. As you are treated with Flagyl, you may start to feel better, but that does not mean the infection is entirely gone. Take all of the medication that was prescribed to you unless instructed to stop taking it by a healthcare professional. Stopping the medication before the bacterial infection is completely gone can result in serious consequences. A stronger strain of bacteria may develop, or the infection may come back again and be more difficult to treat.

What Are The Side Effects?

The most serious side effects from Flagyl are seizures and tingling or numbness in the extremities (arms, legs, hands, and feet). If you experience these symptoms, stop taking Flagyl and call your doctor immediately.

Other side effects include abdominal cramping, diarrhea, headache, nausea, loss of appetite, and vomiting. See the Flagyl side effects page for a more complete list.

What Medications Can Flagyl Interact With?

Flagyl could interact with several drugs. Tell the prescribing physician about all drugs and nutritional supplements you are currently taking, especially those from the following list, which may interact with Flagyl.
  • Alcohol
  • Amprenavir
  • Anticoagulants (such as Warfarin)
  • Barbiturate medicines for inducing sleep or treating seizures (convulsions)
  • Carbamazepine
  • Cimetidine
  • Disulfiram (Antabuse)
  • Dofetilide
  • Fluorouracil
  • Lithium
  • Methadone
  • Phenytoin
  • Sirolimus
  • Tacrolimus

Are There Any Food Interactions?

Alcoholic beverages should not be consumed until 72 hours (3 days) after the last dose of Flagyl is taken. Consuming alcohol while taking Flagyl could result in abdominal cramps, nausea, vomiting, headaches, and flushing. Flagyl can also change the taste of alcohol. Take care to avoid alcohol from unexpected sources, such as over-the-counter cough suppressants or cold products (NyQuil, for example).

Is Flagyl Safe During Pregnancy?

Pregnant women in their first trimester should avoid Flagyl.

The FDA has classified Flagyl as a type B drug. The effect that Flagyl has on an unborn child has not been studied extensively. Flagyl should only be used during pregnancy if it is clearly needed. Notify the prescribing doctor if you become pregnant while you are taking Flagyl. Flagyl does pass into breast milk and could affect a nursing infant. It should be used with care in nursing mothers.

I Have Heard That Milk Thistle Should Be Taken Along With Flagyl -- Why?

Milk thistle (Silybum marianum) may help to protect the liver from medications that may harm it, such as Flagyl. It has not been studied in direct correlation with Flagyl, but it may be prescribed as a complementary therapy.

Won't This Antibiotic Make My Diarrhea From IBD Worse?

Antibiotics kill off bacteria in the body, and many can't distinguish between "good" and "bad" bacteria. Therefore, with some antibiotics, "good" bacteria in the colon may be killed along with the "bad," resulting in diarrhea. However, Flagyl doesn't tend to cause antibiotic-associated diarrhea -- in fact, it may be a treatment for it.


Pfizer. "FLAGYL U.S. Physician Prescribing Information." Pfizer Inc. Apr 2010. 24 Jan 2012.

The American Society of Health-System Pharmacists, Inc. "Metronidazole Oral." MedLine Plus 1 Sept 2008. 24 Jan 2012.

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