What’s the Buzz

The Bee Healthy Blog

What is Metronidazole Used For?

Metronidazole (brand name: Flagyl) is a commonly prescribed antibiotic that is used to treat many bacterial and parasitic infections. Please continue reading to find out more about the types of infections metronidazole is used to treat.

What is metronidazole? How does it work? 

Metronidazole belongs to a group of drugs called nitroimidazole antimicrobials. It can treat infections by interfering with the DNA synthesis of the causative organism, thus causing them to die and preventing them from spreading further. This medication is for adults only but may be prescribed to treat amebiasis in children. Doctors determine metronidazole dosage based on their total body weight. 

What is metronidazole used to treat?


Metronidazole is used to treat sexually transmitted diseases such as trichomoniasis (caused by a parasite called Trichomonas vaginalis). It is given to symptomatic patients with confirmed trichomoniasis. It is also given to asymptomatic females who have inflammation of the cervical tissues. 

In addition, metronidazole is usually simultaneously prescribed to asymptomatic sexual partners of treated patients to prevent reinfection.


Metronidazole is prescribed for an acute stomach or intestinal disease called amebiasis, (also referred to as amebic dysentery), which is caused by a parasite called Entamoeba histolytica. 

Metronidazole is also used, along with surgical drainage of an abscess, in patients with amebic liver abscesses.


Metronidazole is used for the treatment of a diarrheal disease called giardiasis (caused by a protozoan called Giardia lamblia).


Metronidazole is effective against an intestinal protozoan parasite called Balantidium coli that causes balantidiasis (diarrhea and abdominal pain). However, this type of infection is uncommon in the United States.

Anaerobic bacterial infections

Metronidazole is used to treat bacterial infections caused by susceptible anaerobic bacteria.  

Surgical procedures may be used along with metronidazole therapy when appropriate. When treating a mixed aerobic and anaerobic infection, metronidazole should be used in combination with other antimicrobial agents for appropriate coverage. 

For serious anaerobic infections, intravenous metronidazole may be used initially, followed by metronidazole oral dosage forms. Some of the anaerobic bacterial infections treated with metronidazole include:

  • Abdominal infections like peritonitis, liver abscesses, and intra-abdominal abscesses

  • Skin and skin structure infections

  • Gynecologic infections such as tubo-ovarian abscesses, endometritis, endomyometritis, pelvic inflammatory disease, and post-surgical vaginal cuff infections

  • Bacterial septicemia (blood infections)

  • Bone and joint infections

  • Central nervous system infections such as meningitis and brain abscesses

  • Lower respiratory tract infections such as pneumonia, lung abscesses, and empyema

  • Heart infections such as endocarditis

Bacterial vaginosis

Metronidazole extended-release tablets and topical metronidazole (vaginal gel and cream forms) are used to treat bacterial vaginosis (vaginal infections caused by bacteria). However, this medicine cannot be used to treat vaginal infections such as vaginal yeast infection (fungal infection). In fact, a new vaginal yeast infection can be a side effect of metronidazole treatment. Call your doctor if you develop signs of a fungal infection after taking metronidazole (symptoms may include vaginal itching, burning, redness, swelling, and pain). Your doctor may prescribe an antifungal medication.


Topical metronidazole may be prescribed for rosacea to treat the inflammatory lesions associated with this skin condition. 

How to take metronidazole?

Metronidazole tablets, capsules, and extended-release tablets should be taken by mouth with water. The dose of metronidazole will differ depending on the infection being treated. 

For example, to treat trichomoniasis, the usual dose is 2 grams by mouth to be taken as a single, one-time dose or as two divided doses, 1 gram taken in the morning and 1 gram in the evening. 

The typical dosage to treat anaerobic bacterial infection in adults is generally 500 milligrams (m) every 6 hours with a therapy duration of 7 to 10 days. The maximum amount is 4 grams within 24 hours. 

You should take the extended-release tablet without food at least 1 hour before or 2 hours after a meal. Swallow it whole — do not cut, crush, or chew an extended-release tablet. 

Read the prescription label carefully and take the metronidazole oral tablet exactly as prescribed. Do not change the dose, dosage frequency, or treatment duration without your doctor’s approval. Continue taking metronidazole even if you no longer have any symptoms. Stopping treatment too soon can cause your infection to come back and be more difficult to treat in the future.

Keep all your medical and lab appointments while on metronidazole. Your doctor may want to order certain medical tests and adjust your treatment course.

Metronidazole is an antibiotic, and it cannot treat a viral infection such as the common cold, flu, or other viral infections. To prevent the development of drug resistance in bacteria and maintain the effectiveness of metronidazole and other antibacterial drugs, you should only take metronidazole to treat or prevent infections that are proven or strongly suspected to be caused by bacteria that are susceptible to this antibiotic. Your doctor will order a culture and susceptibility test and select the antibacterial therapy based on the results or choose an antibiotic according to local susceptibility patterns.

What are the side effects of metronidazole?

Common side effects in patients treated with metronidazole include upset stomach, stomach pain, stomach cramps, nausea, vomiting, diarrhea, constipation, loss of appetite, headache, unpleasant or metallic taste, and dry mouth. 

Developing a furry tongue can be a side effect of oral metronidazole and other antibiotics. However, this is rare and painless. Good oral hygiene and avoiding tobacco use can help prevent this side effect. Call your doctor for medical advice if these side effects are severe or do not go away after a few days once your body has had a chance to get used to metronidazole.

More serious adverse effects of metronidazole are listed below. Seek immediate medical attention if you develop:

  • An allergic reaction (severe skin reaction) with skin rash, skin pain, hives, itching, peeling or blistering skin

  • Numbness, tingling, burning, or pain in the hands or feet

  • Seizures

  • New or worsening symptoms of infection, such as fever, chills, sore throat, or stuffy nose

  • Worsening yeast infection

  • Difficulties with coordination

  • Painful or difficult urination

What precautions should I take while on metronidazole?

Allergic reactions

Tell your doctor if you have a history of allergic reactions to metronidazole, other antibiotics, or any other medications.

Drug interactions

Give your doctor a complete list of your medications, including prescription drugs, over-the-counter medications, dietary supplements, and herbal remedies. This can help avoid potentially dangerous drug interactions with other drugs.

Medical history

Give your doctor a complete medical history. Metronidazole may not be right for people with certain medical conditions such as liver disease, kidney disease, or if you are undergoing dialysis, Crohn’s disease, a blood cell disorder, medical problems affecting the brain, and QT prolongation. Your doctor may need to adjust your dose or choose another antibiotic.

Missed dose

If you miss a dose of metronidazole, take it as soon as you remember. However, if it is almost time for your next dose, skip the missed dose and go back to your regular dosing schedule. Do not take two doses together or extra medicine to make up for a missed dose.


In case of an overdose, call your local poison control center or the national poison control center on 1-800-222-1222. Call 911 if someone has collapsed, stopped breathing, had a seizure, or is unresponsive. Overdose symptoms may include nausea, vomiting, numbness or pain in the hands and feet, poor coordination (problems with balance or muscle movement), and seizures.

Pregnancy and lactation

Tell your doctor if you are pregnant or breastfeeding. Call your doctor if you become pregnant during metronidazole treatment. This antibiotic can harm the unborn baby if a pregnant woman takes it in the first trimester (early pregnancy).


Do not drink alcohol or take products containing propylene glycol while on metronidazole and for 3 days after your last dose. Drinking alcohol while on metronidazole may cause nausea, vomiting, stomach cramps, sweating, flushing, and headaches.

Frequently Asked Questions

What STD is metronidazole 500 mg used for?

Metronidazole oral tablet is used for sexually transmitted infections called trichomoniasis caused by Trichomonas vaginalis, a protozoan parasite. The usual treatment in women with trichomoniasis is a 7-day course of metronidazole 375 mg twice a day. This treatment helps to minimize reinfection by providing protection long enough until the sexual partner can obtain treatment. Repeat courses of metronidazole are usually given at an interval of 4-6 weeks if needed after trichomoniasis has been confirmed in the laboratory. 

Is metronidazole used for UTI?

Metronidazole is not typically used for UTI (urinary tract infection). Antibiotics that are commonly prescribed for uncomplicated UTIs include trimethoprim and sulfamethoxazole (Bactrim, Bactrim DS), nitrofurantoin (Macrodantin, Macrobid, Furadantin), fosfomycin (Monurol), cephalexin, and ceftriaxone.

Is metronidazole a strong antibiotic?

Metronidazole is a strong antibiotic and is particularly effective against certain parasites and anaerobic bacteria.

How quickly does metronidazole work? 

For most infections, you should start to feel better within a few days of starting metronidazole. However, for some infections, it may take a week to notice an improvement in your symptoms. You should finish the entire course of metronidazole exactly as prescribed to prevent bacterial resistance. 



  1. https://medlineplus.gov/druginfo/meds/a689011.html

  2. https://dailymed.nlm.nih.gov/dailymed/lookup.cfm?setid=a2883ca1-5a9a-4259-9d80-46ab67274384

  3. https://www.ncbi.nlm.nih.gov/books/NBK539728/#