Metronidazole (Systemic)

Adult Medication

Brand Names: US

First-Metronidazole 100; First-Metronidazole 50; Flagyl; Flagyl ER; Metro

Brand Names: Canada

Flagyl; Metronidazole Injection USP; Novo-Nidazol; PMS-Metronidazole


  • Metronidazole has been shown to cause cancer in mice and rats with long-term use. Talk with the doctor.
  • Do not use this drug for other health problems.

What is this drug used for?

  • It is used to treat infections.
  • It is used to prevent infections during bowel surgery.
  • It may be given to you for other reasons. Talk with the doctor.

What do I need to tell my doctor BEFORE I take this drug?

  • If you have an allergy to metronidazole or any other part of this drug.
  • If you are allergic to any drugs like this one, any other drugs, foods, or other substances. Tell your doctor about the allergy and what signs you had, like rash; hives; itching; shortness of breath; wheezing; cough; swelling of face, lips, tongue, or throat; or any other signs.
  • If you have taken disulfiram within the past 2 weeks.
  • If you are less than 12 weeks pregnant. This drug is not for use in certain patients who are less than 12 weeks pregnant.
  • If you are breast-feeding or plan to breast-feed.
This is not a list of all drugs or health problems that interact with this drug.
Tell your doctor and pharmacist about all of your drugs (prescription or OTC, natural products, vitamins) and health problems. You must check to make sure that it is safe for you to take this drug with all of your drugs and health problems. Do not start, stop, or change the dose of any drug without checking with your doctor.

What are some things I need to know or do while I take this drug?

  • Tell all of your health care providers that you take this drug. This includes your doctors, nurses, pharmacists, and dentists.
  • Have blood work checked as you have been told by the doctor. Talk with the doctor.
  • This drug may affect certain lab tests. Tell all of your health care providers and lab workers that you take this drug.
  • This drug may affect how much of some other drugs are in your body. If you are taking other drugs, talk with your doctor. You may need to have your blood work checked more closely while taking this drug with your other drugs.
  • Avoid alcohol and products that have alcohol or propylene glycol in them while taking this drug and for at least 72 hours after your last dose. Drinking alcohol or taking products that have alcohol or propylene glycol in them, like some cough syrups, may cause cramps, upset stomach, headaches, and flushing.
  • Do not use longer than you have been told. A second infection may happen.
  • If you are 65 or older, use this drug with care. You could have more side effects.
  • Tell your doctor if you are pregnant or plan on getting pregnant. You will need to talk about the benefits and risks of using this drug while you are pregnant.

What are some side effects that I need to call my doctor about right away?

WARNING/CAUTION: Even though it may be rare, some people may have very bad and sometimes deadly side effects when taking a drug. Tell your doctor or get medical help right away if you have any of the following signs or symptoms that may be related to a very bad side effect:

All products:

  • Signs of an allergic reaction, like rash; hives; itching; red, swollen, blistered, or peeling skin with or without fever; wheezing; tightness in the chest or throat; trouble breathing or talking; unusual hoarseness; or swelling of the mouth, face, lips, tongue, or throat.
  • Change in balance.
  • Dizziness or passing out.
  • Trouble speaking.
  • Seizures.
  • Change in eyesight.
  • Feeling irritable.
  • Low mood (depression).
  • Feeling tired or weak.
  • Not able to sleep.
  • Redness or white patches in mouth or throat.
  • Some people who took this drug for a long time have had nerve problems that lasted for a long time. Call your doctor right away if you have a burning, numbness, or tingling feeling that is not normal.
  • This drug may raise the chance of a very bad brain problem called aseptic meningitis. Call your doctor right away if you have a headache, fever, chills, very upset stomach or throwing up, stiff neck, rash, bright lights bother your eyes, feeling sleepy, or feeling confused.


  • Pain and irritation where this drug goes into the body.
  • Swelling in the feet or hands.

What are some other side effects of this drug?

All drugs may cause side effects. However, many people have no side effects or only have minor side effects. Call your doctor or get medical help if any of these side effects or any other side effects bother you or do not go away:
  • Upset stomach or throwing up.
  • Loose stools (diarrhea).
  • Hard stools (constipation).
  • Not hungry.
  • Stomach cramps.
  • Metallic taste.
These are not all of the side effects that may occur. If you have questions about side effects, call your doctor. Call your doctor for medical advice about side effects.
You may report side effects to your national health agency.

How is this drug best taken?

Use this drug as ordered by your doctor. Read all information given to you. Follow all instructions closely.

All oral products:

  • To gain the most benefit, do not miss doses.
  • Keep taking this drug as you have been told by your doctor or other health care provider, even if you feel well.

Short-acting products:

  • Take with or without food. Take with food if it causes an upset stomach.

Long-acting products:

  • Take on an empty stomach. Take 1 hour before or 2 hours after meals.
  • Swallow whole. Do not chew, break, or crush.


  • It is given as an infusion into a vein over a period of time.

What do I do if I miss a dose?

All oral products:

  • Take a missed dose as soon as you think about it.
  • If it is close to the time for your next dose, skip the missed dose and go back to your normal time.
  • Do not take 2 doses at the same time or extra doses.


  • Call your doctor to find out what to do.

How do I store and/or throw out this drug?

All oral products:

  • Store at room temperature.
  • Store in a dry place. Do not store in a bathroom.


  • If you need to store this drug at home, talk with your doctor, nurse, or pharmacist about how to store it.

All products:

  • Keep all drugs in a safe place. Keep all drugs out of the reach of children and pets.
  • Check with your pharmacist about how to throw out unused drugs.

General drug facts

  • If your symptoms or health problems do not get better or if they become worse, call your doctor.
  • Do not share your drugs with others and do not take anyone else’s drugs.
  • Keep a list of all your drugs (prescription, natural products, vitamins, OTC) with you. Give this list to your doctor.
  • Talk with the doctor before starting any new drug, including prescription or OTC, natural products, or vitamins.
  • Some drugs may have another patient information leaflet. If you have any questions about this drug, please talk with your doctor, nurse, pharmacist, or other health care provider.
  • If you think there has been an overdose, call your poison control center or get medical care right away. Be ready to tell or show what was taken, how much, and when it happened.

Consumer Information Use and Disclaimer

This information should not be used to decide whether or not to take this medicine or any other medicine. Only the healthcare provider has the knowledge and training to decide which medicines are right for a specific patient. This information does not endorse any medicine as safe, effective, or approved for treating any patient or health condition. This is only a brief summary of general information about this medicine. It does NOT include all information about the possible uses, directions, warnings, precautions, interactions, adverse effects, or risks that may apply to this medicine. This information is not specific medical advice and does not replace information you receive from the healthcare provider. You must talk with the healthcare provider for complete information about the risks and benefits of using this medicine.

Last Reviewed Date



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