Flagyl (Metronidazole)

(℞) Prescription Required

    Flagyl (Metronidazole) Dosage and Side Effects

    FLAGYL works by killing bacteria and parasites that cause infections in your body. It can be used to treat:

    • infections of the genital tract (such as trichomoniasis: a sexually transmitted infection, bacterial vaginosis);
    • stomach, liver and intestinal infections (amebiasis, giardiasis);
    • infections (such as intra-abdominal, brain or lung infections), caused by anaerobic bacteria (bacteria that are able to survive in the absence of oxygen).

    Warnings and Precautions

    BEFORE you use FLAGYL talk to your doctor or pharmacist if you:

    • are pregnant, think you are, or plan to get pregnant
    • are breastfeeding, or planning to breastfeed, as metronidazole is excreted in human breast milk
    • have liver problems
    • have any allergies to this drug or its ingredients (see What the nonmedicinal ingredients are:) or a known allergy to nitroimidazoles (e.g. tinidazole)
    • have an active or chronic severe disease of the nervous system
    • have any blood disorder (e.g. leukemia, hemophilia, or other). Your doctor may order periodic blood tests.
    • have a thyroid condition or hypoadrenalism (underactive adrenal glands)

    Contact your doctor if the following occurs while taking FLAGYL:

    • You feel sleepy, dizzy, confused, see or hear things that are not there (hallucinations), have fits (convulsions), have temporary eyesight problems ( e.g. blurred or double vision). If this happens do not drive or use machinery or tools
    • You feel tingling, pain, numbness or weakness in the arms or legs ( peripheral neuropathy)

    Unnecessary use of FLAGYL should be avoided and prolonged treatment duration should be carefully weighed by your doctor. Its use should be reserved for the conditions described in the “What the medication is used for:” section.

    Avoid alcohol during FLAGYL treatment and for at least one day following treatment to avoid an adverse reaction.

    If a sexual partner shows signs of infection, the partner should be examined and treated by the doctor too.

    If you have liver problems, your doctor may tell you to use a lower dose or to use the medicine less often. FLAGYL may darken your urine and this is not considered a concern.

    Side Effects

    Like all medicines, FLAGYL can cause side effects, although not everybody gets them.

    These side effects may include:

    • Unpleasant taste in the mouth
    • Furred tongue or tongue discoloration
    • Feeling sick (nausea), being sick (vomiting), upset stomach, stomach pain or diarrhea
    • Loss of appetite
    • Feeling sleepy or dizzy

    This is not a complete list of side effects. For any unexpected side effects while taking FLAGYL, contact your doctor or pharmacist.

    Interactions with this medication

    Please tell your doctor or pharmacist if you are taking or have recently taken any other medicines. This includes medicines obtained without a prescription, including herbal medicines. This is because FLAGYL can affect the way some other medicines work. Also, some other medicines can affect the way FLAGYL works.

    In particular tell your doctor if you are taking any of the following medicines:

    • Medicines used to thin the blood such as warfarin (Coumadin);
    • Lithium;
    • Phenobarbital;
    • Phenytoin (Dilantin);
    • 5-fluorouracil (or 5-FU);
    • Busulfan (Myleran);
    • Cyclosporin (Neoral);
    • Disulfiram;
    • Vecuronium.

    If you are not sure, talk to your doctor or pharmacist before taking FLAGYL.

    Do not drink any alcohol while you are taking FLAGYL and for at least 1 day after finishing your course. Drinking alcohol while using FLAGYL might cause unpleasant side effects, such as feeling sick (nausea), being sick (vomiting), stomach pain, hot flushes, very fast or uneven heartbeat (palpitations) and headache.

    Proper Use of this medication

    Usual adult dose:

    Treatment of Trichomoniasis:

    Oral Administration:

    Single-Dose Treatment:

    For both women and men, 2 g (4 capsules) administered as a single dose after a meal.

    Standard Ten-day Treatment:

    • Women: One 250 mg tablet twice a day, morning and night for 10 consecutive days.
    • Men: One 250 mg tablet twice a day for 10 consecutive days.

    For both men and women, it may be occasionally necessary to give a second ten-day course after 4 to 6 weeks.

    Vaginal Treatment:

    Cream—One applicator full of FLAGYL Cream (500 mg) once or twice a day into the vagina for 10 or 20 consecutive days even during menstruation.

    The applicator should not be used after the 7th month of pregnancy.

    Treatment of Amebiasis:


    Intestinal Amebiasis—Three 250 mg tablets three times daily for 5 to 7 days.

    Amebic abscesses of the liver—Two to three 250 mg tablets three times daily for 5 to 7 days.


    Administer 35 to 50 mg/kg/day in three divided doses for 5 to 7 days.

    Treatment of Giardiasis:


    One 250 mg tablet twice daily for 5 to 7 days.


    Administer 25 to 35 mg/kg/day in two divided doses for 5 to 7 days.

    Treatment of Bacterial Vaginosis:


    500 mg orally twice a day for 7 days.

    Concurrent treatment of sexual partners is not usually indicated.

    Anaerobic Infections:


    In the treatment of most serious anaerobic infections, intravenous metronidazole is usually administered initially. This may be followed by oral therapy with FLAGYL capsules.

    Oral Administration:

    500 mg every 8 hours. Treatment for seven days should be satisfactory for most patients.



    In case of drug overdose, contact a health care practitioner, hospital emergency department or regional Poison Control Centre immediately, even if there are no symptoms.

    Missed dose:

    If you forget to take FLAGYL, take it as soon as you remember. However, if it is almost time for your next dose, skip the missed dose. Do not use a double dose to make up for a forgotten dose.

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    The above information is an educational aid only. It is not intended as medical advice for individual conditions or treatments. Talk to your doctor, nurse or pharmacist before following any medical regimen to see if it is safe and effective for you.

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