GENERIC NAME: Metronidazole

COMMON BRAND: Flagyl, Flagyl ER

Metronidazole is an oral prescription antibiotic, belongs to a class of drugs known as nitroimidazole antimicrobials. This drug acts by stopping the growth of bacteria or parasites. It is available as the brand-name drug and generic drug. Generic drugs usually cost less.

Metronidazole comes in various forms such as an oral tablet, oral capsule, cream, gel, and lotion and vaginal gel. It is also available as an injectable medication given by a healthcare provider.

What is Metronidazole (Flagyl) used for treating?

Metronidazole is used to treat infections of gastrointestinal (GI) tract, reproductive system, respiratory tract, heart, skin, bone, joint, blood, nervous system, and other areas of the body. It is also used to treat STDs (sexually transmitted diseases), and long-acting tablets of metronidazole are used to treat bacterial vaginosis (infection due to too much of bacteria in the vagina) in women.

Metronidazole also used with other medications to treat stomach/intestinal ulcers caused by H. pylori bacteria.

This antibiotic is used to treat only certain bacterial and parasitic infections. However, this drug will not work for colds, flu, or other virus infections.

How to use Metronidazole (Flagyl)?

Follow all the direction on your prescription label carefully, and discuss with your doctor or pharmacist about any part you do not understand. Take metronidazole exactly as prescribed. Do not alter your dose or take it more frequently than prescribed by your doctor.

The dose is based on your medical condition and response to treatment. Take metronidazole orally as directed by your doctor, usually once per day (or divided into two doses on day 1) or two to four times daily for up to 10 days or longer. Metronidazole long-acting tablets are usually taken once daily at least 1 hour before or 2 hours after a meal for seven days.

Take this drug regularly even if you feel better to get the full benefit from it. Preferably take medicine at the same time each day to avoid confusion.

Do not stop or skip doses of this drug even if you feel better, if stopping of this medication too early may result in a return of the infection, or you become resistant to antibiotics.

What are the side effects of Metronidazole (Flagyl)?

The most commonly observed side effects with this drug such as a headache, loss of appetite, nausea or vomiting, diarrhea, heartburn, cramping in your stomach area, constipation, metallic taste. If any of the above side effects remain or get worse, talk to your doctor or pharmacist immediately.

Get emergency medical assistance promptly if you notice serious side effects like unsteadiness, seizures, mental/mood changes (such as confusion), trouble speaking, numbness/tingling of arms/legs, eye pain, sudden vision changes, signs of a new infection (such as a sore throat that doesn’t go away, fever), easy bruising/bleeding, stomach/abdominal pain, painful urination.

This drug may turn your urine to darken in colour which is harmless and will disappear when the medication is discontinued.

Allergic reaction to this medicine is very rare. However, get medical help promptly if you notice any symptoms of a severe allergic reaction, such as rash, itching/swelling (face/tongue/throat), breathlessness.

Prolonged or frequent use of this medication may result in oral thrush or a new yeast infection. Talk to your doctor if you notice white patches in your mouth, a change in vaginal discharge, or any other new symptoms.

This is not a full record of all possible side effects. If you mark other effects not listed above, contact your doctor or pharmacist.

What are the precautions while using Metronidazole (Flagyl)?

Before using this drug, notify your doctor or pharmacist if you are allergic to it or if you have any other allergies.

Tell your doctor about your medical history, mainly of liver disease, kidney disease, certain blood disorders (low blood cell counts).

People with Cockayne syndrome (a rare genetic disorder) may be at high risk for severe liver disease with the use of metronidazole. Get emergency medical assistance right away if you notice any signs of liver disease during treatment (like nausea/vomiting that doesn’t stop, loss of appetite, severe stomach/abdominal pain, yellowing eyes/skin, dark urine).

Metronidazole may decrease the effectiveness of live bacterial vaccines (like typhoid vaccine). Avoid any immunizations/vaccinations while using this medication unless your doctor tells you to.

Do not drink alcoholic beverages or products containing propylene glycol with this drug and for at least three days after your last dose. Alcohol and propylene glycol may cause a headache, nausea, vomiting, stomach cramps, sweating, and flushing (redness of the face) when taken with metronidazole.

In pregnancy, this drug should be used only when benefits outweigh the risk. This drug may also cross into breast milk. Ask your doctor for any further information.

What are the drug interactions of Metronidazole (Flagyl)?

Metronidazole may interact with other medications, vitamins, or herbs you may be using. A drug interaction is when a substance changes the way a drug works which can be harmful or hinder the drug from working well.

Do not take disulfiram with metronidazole as this combination may cause severe effects in your body. Using this combination can cause psychotic reactions like confusion, hallucinations, delusions (believing things that aren’t real). Do not take metronidazole if you have taken disulfiram in the last two weeks.

Some products that may interact with metronidazole include alcohol-containing products (like a cough and cold syrups), products containing lithium, propylene glycol, lopinavir/ritonavir solution.

This medication may intervene with certain lab tests, resulting in a false test. Assure that all your doctors and lab personnel know you use this drug.


Cancer was found in some animals during preclinical testing with metronidazole. There may be chances of similar risk in humans. As of this risk, metronidazole should only be used to treat conditions as approved by the FDA.

To avoid the occurrence of drug-resistant bacteria, metronidazole should only be used to treat or prevent infections that are strongly assumed to be caused by bacteria.

What are the forms and strengths of Metronidazole (Flagyl)?

Generic: Metronidazole
Form: Immediate-release oral tablet
Strengths: 250mg, 500mg

Brand: Flagyl
Form: Immediate-release oral tablet
Strengths: 250mg, 500mg

Form: Capsule
Strengths: 375mg

What is the dosage of Metronidazole (Flagyl)?

For Bacterial Infections:

Adult (18–64 years):

Initial dose: 500mg four times per day for 7–10 days. But, some infections may require more prolonged treatment.
Maximum dosage: 4g per day.

For Amoebic Infections:

Initial dose: 500mg or 750mg three times per day for 5–10 days.

For Trichomoniasis:

Initial dose: Either 2g as a single dose or in two divided doses of 1g each on a single day or 250mg three times per day for seven days.

For Bacterial Vaginosis:

Typical dosage: 750mg per day for seven days.

For Amoebic Infections:

Children (0 to 17 years):

Initial dose: 35 to 50mg/kg of body weight per day given in three divided doses for ten days.

Geriatric (65 years and above):

In older adults, the dose of the drug needs to be reduced, or given at a different schedule because older adults eliminate drugs more slowly. This avoids the building of medicine in the body.

Most common questions asked about Metronidazole / Q&A’s:

What happens if you drink alcohol with Metronidazole?

Metronidazole is contraindicated with alcohol. It can react with the little amount of alcohol, and this is the reason you must avoid alcohol for at least 48 hours of taking metronidazole, as it takes at least 48 hours for metronidazole to eliminate from the body of an adult. Metronidazole and alcohol can cause severe side effects such as headaches, stomach ache, hot flushes and fast or irregular heartbeat.

Can you take Metronidazole while pregnant?

There is no evidence that suggests using metronidazole during pregnancy can cause birth defects or increase the risk of miscarriage. However, discuss with your doctor or pharmacist before using metronidazole.

Does Metronidazole treat urinary tract infection (UTI)?

Studies conducted on oral metronidazole versus oral ampicillin in women who had symptoms of urinary tract infection (UTI) and a positive culture for Gardnerella vaginalis (bacterial vaginosis). The studies suggested that metronidazole was as effective as ampicillin. However, adverse events were observed in patients treated with metronidazole, as compared to patients treated with ampicillin. Therefore, metronidazole is not a drug of choice for the treatment of urinary tract infection (UTI).

What sexually transmitted disease (STD) is treated with Metronidazole?

Trichomoniasis (Trichomonas vaginalis) is the most common curable sexually transmitted disease (STD) in women, which is characterized by malodorous, yellow-greenish vaginal discharge and vulvar irritation. Oral metronidazole is used to treat Trichomoniasis. Topical metronidazole is not used for the treatment of trichomoniasis in pregnant and nonpregnant women.

What types of infections is Metronidazole used for?

Metronidazole is an antibiotic, used for the treatment of various bacterial infections of the vagina, stomach, skin, liver, joints, brain and respiratory tract.


TheMedPharma has made every effort to make sure that all the information is factually correct, comprehensive, and up-to-date. However, this website should not be considered as a substitute for the advice, knowledge and expertise of a licensed healthcare professional. You should always consult your doctor or licensed health care professional before taking any medication. The drug information contained herein is subjected to changes if required. The lack of warnings or other information for a given drug does not mean that the drug or its combination is safe, effective or appropriate for use in all patients.