Metronidazole belongs to the class of medications called antibiotics. It is used to treat infections caused by certain bacteria. It is most commonly used for abdominal, vaginal, and intestinal infections. Metronidazole works by killing bacteria and parasites.

This medication may be available under multiple brand names and/or in several different forms. Any specific brand name of this medication may not be available in all of the forms or approved for all of the conditions discussed here. As well, some forms of this medication may not be used for all of the conditions discussed here.

Your doctor may have suggested this medication for conditions other than those listed in these drug information articles. If you have not discussed this with your doctor or are not sure why you are taking this medication, speak to your doctor. Do not stop taking this medication without consulting your doctor.

Do not give this medication to anyone else, even if they have the same symptoms as you do. It can be harmful for people to take this medication if their doctor has not prescribed it.

The dose of metronidazole depends on the condition being treated. The usual adult dose of metronidazole is 500 mg taken by mouth every 8 hours or twice daily. For treatment of trichomoniasis, a single dose of 2,000 mg may be taken orally after a meal. Many other doses exist according to the infection being treated, and range from 250 mg taken by mouth 2 times daily to 750 mg taken by mouth 3 times daily.

Metronidazole may be taken with or without food. If it causes stomach upset, it is best taken with food or milk.

Metronidazole vaginal cream or gel is used for vaginal infections. The dose is applied into the vagina usually once or twice a day. See the package insert or talk to your health care provider about how to use the applicator correctly.

Many things can affect the dose of medication that a person needs, such as body weight, other medical conditions, and other medications. If your doctor has recommended a dose different from the ones given here, do not change the way that you are taking the medication without consulting your doctor.

It is important to take this medication regularly and exactly as prescribed by the doctor. Keep taking this medication until the prescription is complete even if you feel better. If you stop taking the medication too early, the infection may return and be harder to treat.

If you miss a dose, take it as soon as possible and continue with your regular schedule. If it is almost time for your next dose, skip the missed dose and continue with your regular dosing schedule. Do not take a double dose to make up for a missed one. If you are not sure what to do after missing a dose, contact your doctor or pharmacist for advice.

Store this medication at room temperature, protect it from light and moisture, and keep it out of the reach of children.

Oral capsules
Each pale green and light grey capsule, printed with a symbol and "500", contains 500 mg of metronidazole. Nonmedicinal ingredients: black ink, D&C Red No. 33, D&C Yellow No. 10, FD&C Blue No. 1, FD&C Green No. 3, gelatin, lactose monohydrate, magnesium stearate, polacrilin potassium, silicon dioxide, sodium lauryl sulfate, and titanium dioxide. Tartrazine-free.

Vaginal cream
Each tube contains metronidazole 10% w/w in a cream base. Nonmedicinal ingredients: glycerin, glyceryl monostearate, methylparaben, propylparaben, purified water, stearic acid, and trolamine. Tartrazine-free.

Do not take this medication if you:

• are allergic to metronidazole or any ingredients of the medication
• have a history of blood disorders
• have a brain (neurological) disorder
• have an underactive thyroid (hypothyroidism)
• have underactive adrenal glands (hypoadrenalism)

Many medications can cause side effects. A side effect is an unwanted response to a medication when it is taken in normal doses. Side effects can be mild or severe, temporary or permanent.

The side effects listed below are not experienced by everyone who takes this medication. If you are concerned about side effects, discuss the risks and benefits of this medication with your doctor.

The following side effects have been reported by at least 1% of people taking this medication. Many of these side effects can be managed, and some may go away on their own over time.

Contact your doctor if you experience these side effects and they are severe or bothersome. Your pharmacist may be able to advise you on managing side effects.

• buzzing, ringing, or whistling sound heard in the ears
• change in taste sensation
• coated or furry tongue
• diarrhea
• dizziness or lightheadedness
• headache
• loss of appetite
• nausea
• sleepiness
• stomach pain or cramps
• unpleasant or sharp metallic taste
• vomiting

Although most of the side effects listed below don't happen very often, they could lead to serious problems if you do not seek medical attention.

Check with your doctor as soon as possible if any of the following side effects occur:

• any vaginal irritation, discharge, or dryness not present before use of this medicine
• bruising
• confusion
• eye pain
• fever or unexpected infections
• gum bleeding
• hallucinations
• hearing loss
• mouth ulcers
• numbness, tingling, pain, or weakness in hands or feet
• signs of depression (e.g., poor concentration, changes in weight, changes in sleep, decreased interest in activities, thoughts of suicide)
• signs of liver problems (e.g., nausea, vomiting, diarrhea, loss of appetite, weight loss, yellowing of the skin or whites of the eyes, dark urine, pale stools)
• skin rash, redness, or itching
• vision changes

Stop taking the medication and seek immediate medical attention if any of the following occur:

• convulsions (seizures)
• difficulty coordinating body movement
• extreme sensitivity to bright light
• severe watery or bloody diarrhea
• signs of pancreatitis (e.g., abdominal pain on the upper left side, back pain, nausea, fever, chills, rapid heartbeat, swollen abdomen)
• signs of a serious allergic reaction (e.g., difficulty breathing, itchy skin rash, swelling of face or throat, wheezing)
• signs of a severe skin reaction such as blistering, peeling, a rash covering a large area of the body, a rash that spreads quickly, or a rash combined with fever or discomfort
• stiff neck along with a headache

Some people may experience side effects other than those listed. Check with your doctor if you notice any symptom that worries you while you are taking this medication.

Before you begin using a medication, be sure to inform your doctor of any medical conditions or allergies you may have, any medications you are taking, whether you are pregnant or breast-feeding, and any other significant facts about your health. These factors may affect how you should use this medication.

Alcohol: A severe set of side effects including nausea, vomiting, and rapid heartbeat may occur if you drink alcohol while taking metronidazole. If you are taking this medication, wait until at least one day after finishing metronidazole treatment before drinking alcohol.

Antibiotic-related diarrhea: As with other antibacterials, metronidazole can in rare instances cause a severe form of diarrhea associated with a condition known as pseudomembranous colitis. If you develop severe diarrhea while taking (or within a few weeks of taking) this medication, contact your doctor.

Bacterial resistance: Misuse of an antibiotic such as metronidazole may lead to the growth of resistant bacteria that will not be killed by the antibiotic. If this happens, the antibiotic may not work for you in the future. Although you may begin to feel better early in your course of treatment with metronidazole, you need to take the full course exactly as directed to finish ridding your body of the infection and to prevent resistant bacteria from taking hold. Do not take metronidazole or other antibiotics to treat a viral infection such as the common cold; antibiotics do not kill viruses, and using them to treat viral infections can lead to the growth of resistant bacteria.

Blood cell counts: This medication may cause low white blood cell counts, which can mean your immune system is weak. If you develop a fever, talk to your doctor as soon as possible. Your doctor may also perform blood tests regularly to monitor your blood cell counts if you are taking this medication for a long period of time.

Confusion/dizziness: This medication may cause confusion or dizziness, affecting the physical and mental abilities needed to drive or operate machinery. Avoid driving or other tasks requiring alertness until you know how this medication affects you.

Liver disease: Decreased liver function or liver disease may cause this medication to build up in the body, causing side effects. If you have liver problems, discuss with your doctor how this medication may affect your medical condition, how your medical condition may affect the dosing and effectiveness of this medication, and whether any special monitoring is needed. Your doctor may want to test your liver function regularly with blood tests while you are taking this medication.

Neurological side effects: Stop treatment with metronidazole and see your doctor if muscle incoordination, seizures, or numbness or tingling in the hands or feet occur.

Pancreatitis: Metronidazole can cause the pancreas to become inflamed. If you have a history of pancreatitis, discuss with your doctor how this medication may affect your medical condition, how your medical condition may affect the dosing and effectiveness of this medication, and whether any special monitoring is needed.

Report signs of pancreatitis such as abdominal pain on the upper left side, back pain, nausea, fever, chills, rapid heartbeat, or swollen abdomen to your doctor immediately.

Pregnancy: Metronidazole crosses the placenta and may affect the development of the baby if it taken during pregnancy. This medication should not be used during pregnancy unless the benefits outweigh the risks. If you become pregnant while taking this medication, contact your doctor immediately.

Breast-feeding: This medication passes into breast milk. If you are breast-feeding and taking metronidazole, it may affect your baby. Talk to your doctor about whether you should continue breast-feeding.

Children: The safety and effectiveness of using this medication have not been established for children.

There may be an interaction between metronidazole and any of the following:

• 5-fluorouracil
• alcohol
• amiodarone
• bacillus Calmette-Guérin (BCG)
• busulfan
• capecitabine
• chlorpromazine
• cholera vaccine
• diazepam
• digoxin
• disopyramide
• dronedarone
• haloperidol
• lenvatinib
• lithium
• lopinavir
• lorazepam
• mebendazole
• methadone
• mycophenolate
• nivolumab
• phenobarbital
• phenytoin
• primidone
• procainamide
• quinine
• ritonavir
• sodium picosulfate
• sotalol
• sulfamethoxazole
• tipranavir
• typhoid vaccine (live)
• warfarin
• ziprasidone

If you are taking any of these medications, speak with your doctor or pharmacist. Depending on your specific circumstances, your doctor may want you to:

• stop taking one of the medications,
• change one of the medications to another,
• change how you are taking one or both of the medications, or
• leave everything as is.

An interaction between two medications does not always mean that you must stop taking one of them. Speak to your doctor about how any drug interactions are being managed or should be managed.

Medications other than those listed above may interact with this medication. Tell your doctor or prescriber about all prescription, over-the-counter (non-prescription), and herbal medications you are taking. Also tell them about any supplements you take. Since caffeine, alcohol, the nicotine from cigarettes, or street drugs can affect the action of many medications, you should let your prescriber know if you use them.