Flagyl for Bacterial Infections

What to Know About the Broad-Spectrum Antibiotic

Flagyl, known as metronidazole or by the brand name Protostat, is an antibacterial drug that is classified as a broad-spectrum antibiotic. Metronidazole is used to treat certain bacterial infections or protozoal infections (a type of parasite).

In some cases, Flagyl may be used to treat infections or other complications of inflammatory bowel disease (IBD). It might be given alternately or at the same time as ciprofloxacin, another type of antibiotic.

This article will discuss Flagyl and how it's used to treat infections. It will also talk about side effects and other important information you need to know.


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

Treatment of IBD Diarrhea

Antibiotics kill off bacteria in the body. But 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." This results in diarrhea.

However, Flagyl doesn't tend to cause antibiotic-associated diarrhea. In fact, it may be a treatment for it.

Precautions and Contraindications

People with an allergy or sensitivity to metronidazole should not take Flagyl. Anyone with liver disease should be closely monitored by their doctor if they take this medication. Yeast infections may get worse while taking Flagyl.

Women should avoid taking Flagyl during the first trimester of pregnancy. According to the Food and Drug Administration (FDA), 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.

Tell your prescribing doctor if you become pregnant while you are taking Flagyl. Flagyl passes into breast milk and could affect a nursing infant. It should be used with caution in people who are breastfeeding.


When taken at home to treat an infection, Flagyl is taken orally in tablet form. In order for Flagyl to effectively kill harmful bacteria, it is important to maintain a consistent level of the drug 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 a problem, try chewing gum. You can also suck on hard candy or ice chips.

If You Miss a Dose

When you miss a dose, take it as soon as you remember. If you need to take the next dose soon, skip the missed dose and only take the next scheduled dose. Don't double up or take more than one dose of Flagyl at a time.

Stopping Flagyl

Do not stop Flagyl before taking all the doses. After a few days of treatment, most people start to feel better. But that doesn't mean the infection is entirely gone. Take all of the medication that was prescribed unless your doctor tells you to stop taking it.

Stopping the medication before the bacterial infection is completely gone can cause serious consequences. A stronger strain of bacteria may develop. The infection may come back again and be more difficult to treat.

Side Effects

The most serious side effects of 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 a doctor immediately.

Other side effects include:

  • Abdominal cramping
  • Diarrhea
  • Headache
  • Nausea
  • Loss of appetite
  • Vomiting
Common Side Effects of Flagyl (Metronidazole)
 Verywell / Gary Ferster

Warnings and Interactions

Flagyl could interact with several drugs. Tell the prescribing doctor about all drugs and nutritional supplements you are taking. You should especially mention these from the following list, which may interact with Flagyl:

  • Alcohol
  • Amprenavir
  • Anticoagulants (such as warfarin)
  • Antabuse (disulfiram)
  • Barbiturate medicines for inducing sleep or treating seizures (convulsions)
  • Carbamazepine
  • Cimetidine
  • Dofetilide
  • Fluorouracil
  • Lithium
  • Methadone
  • Phenytoin
  • Sirolimus
  • Tacrolimus


You should not drink alcoholic beverages until 72 hours (three days) after you take the last dose of Flagyl. Drinking 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 medications (NyQuil, for example).

Milk Thistle

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 relation to Flagyl, but it may be prescribed as a complementary therapy.


Flagyl, also known as metronidazole or by the brand name Protostat is an anti-bacterial drug that treats anaerobic bacterial infections or protozoal infections. It's important to follow your doctor's instructions when you take this medication.

Side effects may include abdominal cramping, diarrhea, nausea, vomiting, loss of appetite, and headache. Some patients experience more serious side effects such as numbness or seizures. If you experience these severe side effects, call your doctor right away.

Frequently Asked Questions

  • How long should I wait to drink alcohol after using Flagyl?

    After the last dose of Flagyl is taken, wait at least 72 hours before drinking any alcohol. Drinking while on Flagyl can cause nausea, abdominal cramps, vomiting, and headaches. Some types of over-the-counter cough suppressant and cold products contain small amounts of alcohol, so be careful if you decide to take one.

  • Is metronidazole available over-the-counter?

    No, metronidazole is not available over the counter. You will need to contact your doctor to receive a prescription.

  • How long does it take metronidazole to work?

    Most people begin to feel better after a few days of taking metronidazole or Flagyl. However, even if you feel better, the infection may still be present, which is why it's important to take the full course of medication as prescribed.

  • Can Flagyl be used for a yeast infection?

    Flagyl should never be used to treat a yeast infection. In fact, using it might worsen the effects of a yeast infection.

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