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# Flagyl ER

Generic name: metronidazole (oral route) [ met-roe-NYE-da-zole ]
Drug classes: Amebicides, Miscellaneous antibiotics

Medically reviewed by Drugs.com. Last updated on Dec 1, 2022.

Oral route(Tablet;Tablet, Extended Release)

Metronidazole has been shown to be carcinogenic in mice and rats. Unnecessary use of the drug should be avoided. Its use should be reserved only for conditions for which it is approved .

The Flagyl ER brand name has been discontinued in the U.S. If generic versions of this product have been approved by the FDA, there may be generic equivalents available.

## Commonly used brand name(s)

In the U.S.

- Flagyl
- Flagyl ER

Available Dosage Forms:

- Tablet
- Capsule
- Powder for Suspension

Therapeutic Class: Antibiotic

Chemical Class: Nitroimidazole

## Uses for Flagyl ER

Metronidazole is used to treat bacterial infections in different areas of the body. The extended-release tablets are used to treat women with vaginal infections (bacterial vaginosis).

Metronidazole belongs to the class of medicines known as antibiotics. It works by killing bacteria or preventing their growth. However, this medicine will not work for colds, flu, or other virus infections.

This medicine is available only with your doctor's prescription.

## Before using Flagyl ER

In deciding to use a medicine, the risks of taking the medicine must be weighed against the good it will do. This is a decision you and your doctor will make. For this medicine, the following should be considered:

### Allergies

Tell your doctor if you have ever had any unusual or allergic reaction to this medicine or any other medicines. Also tell your health care professional if you have any other types of allergies, such as to foods, dyes, preservatives, or animals. For non-prescription products, read the label or package ingredients carefully.

### Pediatric

Appropriate studies have not been performed on the relationship of age to the effects of metronidazole capsules and tablets in the pediatric population, except for the treatment of amebiasis. Safety and efficacy have not been established.

Appropriate studies performed to date have not demonstrated pediatric-specific problems that would limit the usefulness of metronidazole extended-release tablets to treat bacterial vaginosis in teenage females, but should not be used before the start of menstruation.

### Geriatric

Appropriate studies performed to date have not demonstrated geriatric-specific problems that would limit the usefulness of metronidazole in the elderly. However, elderly patients are more likely to have unwanted effects and age-related liver problems, which may require caution and an adjustment in the dose for patients receiving metronidazole.

### Breastfeeding

There are no adequate studies in women for determining infant risk when using this medication during breastfeeding. Weigh the potential benefits against the potential risks before taking this medication while breastfeeding.

### Interactions with medicines

Although certain medicines should not be used together at all, in other cases two different medicines may be used together even if an interaction might occur. In these cases, your doctor may want to change the dose, or other precautions may be necessary. When you are taking this medicine, it is especially important that your healthcare professional know if you are taking any of the medicines listed below. The following interactions have been selected on the basis of their potential significance and are not necessarily all-inclusive.

Using this medicine with any of the following medicines is not recommended. Your doctor may decide not to treat you with this medication or change some of the other medicines you take.

- Amprenavir
- Bepridil
- Cisapride
- Disulfiram
- Dronabinol
- Dronedarone
- Mesoridazine
- Pimozide
- Saquinavir
- Sparfloxacin
- Terfenadine
- Thioridazine
- Ziprasidone

Using this medicine with any of the following medicines is usually not recommended, but may be required in some cases. If both medicines are prescribed together, your doctor may change the dose or how often you use one or both of the medicines.

- Alfuzosin
- Amiodarone
- Amitriptyline
- Anagrelide
- Apomorphine
- Aripiprazole
- Aripiprazole Lauroxil
- Arsenic Trioxide
- Asenapine
- Astemizole
- Atazanavir
- Azithromycin
- Bedaquiline
- Buprenorphine
- Bupropion
- Buserelin
- Busulfan
- Capecitabine
- Ceritinib
- Chloroquine
- Chlorpromazine
- Cholera Vaccine, Live
- Ciprofloxacin
- Citalopram
- Clarithromycin
- Clofazimine
- Clomipramine
- Clothiapine
- Clozapine
- Crizotinib
- Cyclobenzaprine
- Dabrafenib
- Dasatinib
- Degarelix
- Delamanid
- Desipramine
- Deslorelin
- Deutetrabenazine
- Dexmedetomidine
- Disopyramide
- Dofetilide
- Dolasetron
- Domperidone
- Donepezil
- Doxepin
- Doxifluridine
- Droperidol
- Ebastine
- Efavirenz
- Encorafenib
- Entrectinib
- Eribulin
- Erythromycin
- Escitalopram
- Famotidine
- Felbamate
- Fexinidazole
- Fingolimod
- Flecainide
- Fluconazole
- Fluorouracil
- Fluoxetine
- Formoterol
- Foscarnet
- Fosphenytoin
- Galantamine
- Gatifloxacin
- Gemifloxacin
- Glasdegib
- Gonadorelin
- Goserelin
- Granisetron
- Halofantrine
- Haloperidol
- Histrelin
- Hydroquinidine
- Hydroxychloroquine
- Hydroxyzine
- Ibutilide
- Iloperidone
- Imipramine
- Inotuzumab Ozogamicin
- Itraconazole
- Ivabradine
- Ivosidenib
- Ketoconazole
- Lapatinib
- Leuprolide
- Levofloxacin
- Lofexidine
- Lumefantrine
- Macimorelin
- Mebendazole
- Mefloquine
- Methadone
- Mifepristone
- Mizolastine
- Mobocertinib
- Moxifloxacin
- Mycophenolate Mofetil
- Mycophenolic Acid
- Nafarelin
- Nelfinavir
- Nilotinib
- Norfloxacin
- Octreotide
- Ofloxacin
- Olanzapine
- Ondansetron
- Osimertinib
- Oxaliplatin
- Ozanimod
- Pacritinib
- Paliperidone
- Panobinostat
- Papaverine Hydrochloride
- Paroxetine
- Pasireotide
- Pazopanib
- Pentamidine
- Perphenazine
- Pimavanserin
- Pipamperone
- Pitolisant
- Ponesimod
- Posaconazole
- Probucol
- Procainamide
- Prochlorperazine
- Promethazine
- Propafenone
- Protriptyline
- Quetiapine
- Quinidine
- Quinine
- Ranolazine
- Ribociclib
- Risperidone
- Ritonavir
- Selpercatinib
- Sertindole
- Sertraline
- Sevoflurane
- Siponimod
- Sodium Phosphate
- Sodium Phosphate, Dibasic
- Sodium Phosphate, Monobasic
- Solifenacin
- Sorafenib
- Sotalol
- Sulpiride
- Sunitinib
- Tacrolimus
- Tamoxifen
- Tegafur
- Telaprevir
- Telavancin
- Telithromycin
- Tetrabenazine
- Tolterodine
- Toremifene
- Trazodone
- Trimipramine
- Triptorelin
- Vandetanib
- Vardenafil
- Vemurafenib
- Venlafaxine
- Vilanterol
- Vinflunine
- Voclosporin
- Voriconazole
- Vorinostat
- Warfarin
- Zuclopenthixol

Using this medicine with any of the following medicines may cause an increased risk of certain side effects, but using both drugs may be the best treatment for you. If both medicines are prescribed together, your doctor may change the dose or how often you use one or both of the medicines.

- Carbamazepine
- Cholestyramine
- Cyclosporine
- Lithium
- Milk Thistle

### Interactions with food/tobacco/alcohol

Certain medicines should not be used at or around the time of eating food or eating certain types of food since interactions may occur. Using alcohol or tobacco with certain medicines may also cause interactions to occur. The following interactions have been selected on the basis of their potential significance and are not necessarily all-inclusive.

### Other medical problems

The presence of other medical problems may affect the use of this medicine. Make sure you tell your doctor if you have any other medical problems, especially:

- Blood or bone marrow problems, or history of or
- Brain disease (eg, aseptic meningitis, encephalopathy) or
- Leukopenia (low white blood cells), history of or
- Optic neuropathy (eye disease with vision changes), history of or
- Oral thrush (Candida infection) or
- Peripheral neuropathy (nerve problem), history of or
- Seizures, history of or
- Vaginal yeast infection (Candida infection)—Use with caution. May make these conditions worse.

- Cockayne syndrome (genetic disorder)—Should not be used in patients with this condition.

- Kidney disease, end-stage or
- Liver disease, severe—Use with caution. The effects may be increased because of slower removal of the medicine from the body.

## Proper use of Flagyl ER

This section provides information on the proper use of a number of products that contain metronidazole. It may not be specific to Flagyl ER. Please read with care.

Take this medicine only as directed by your doctor. Do not take more of it, do not take it more often, and do not take it for a longer time than your doctor ordered.

The capsules can be taken with or without food. If the medicine upsets your stomach, it is best to take it with a meal or snack.

The extended–release tablet must be taken without food, 1 hour before or 2 hours after a meal.

Swallow the extended-release tablet whole. Do not break, crush, or chew it.

To help clear up your infection completely, keep using this medicine for the full time of treatment, even if you begin to feel better after a few days. If you stop using this medicine too soon, your infection may return.

This medicine works best when there is a constant amount in the blood. To help keep the amount constant, do not miss any doses. Also, it is best to take the doses at evenly spaced times during the day. If you need help planning the best times to take your medicine, check with your doctor.

### Dosing

The dose of this medicine will be different for different patients. Follow your doctor's orders or the directions on the label. The following information includes only the average doses of this medicine. If your dose is different, do not change it unless your doctor tells you to do so.

The amount of medicine that you take depends on the strength of the medicine. Also, the number of doses you take each day, the time allowed between doses, and the length of time you take the medicine depend on the medical problem for which you are using the medicine.

- For oral dosage forms (capsules or tablets):
  - For amebiasis infections:
    - Adults—500 or 750 milligrams (mg) 3 times a day for 5 to 10 days.
    - Children—Dose is based on body weight and must be determined by your doctor. The dose is usually 35 to 50 milligrams (mg) per kilogram (kg) of body weight per day, divided into 3 doses, for 10 days.
  - For bacterial infections:
    - Adults—Dose is based on body weight and must be determined by your doctor. The dose is usually 7.5 milligrams (mg) per kilogram (kg) of body weight every 6 hours for 7 to 10 days. Your doctor may increase your dose as needed. However, the dose is usually not more than 4000 mg per day.
    - Children—Use and dose must be determined by your doctor.
  - For trichomoniasis infections:
    - Adults—The tablet can be given 3 different ways: as a single dose of 2 grams, as 1 gram 2 times a day for 1 day, or as 250 milligrams (mg) 3 times a day for 7 days. The capsule dose is 375 mg 2 times a day for 7 days.
    - Children—Use and dose must be determined by your doctor.
- For oral dosage form (extended-release tablets):
  - For bacterial vaginosis:
    - Adults—750 milligrams (mg) once a day for 7 days.
    - Children—Use and dose must be determined by your doctor.

### Missed dose

If you miss a dose of this medicine, take it as soon as possible. However, if it is almost time for your next dose, skip the missed dose and go back to your regular dosing schedule. Do not double doses.

### Storage

Store the medicine in a closed container at room temperature, away from heat, moisture, and direct light. Keep from freezing.

Keep out of the reach of children.

Do not keep outdated medicine or medicine no longer needed.

Ask your healthcare professional how you should dispose of any medicine you do not use.

Detailed Flagyl ER dosage information

## Precautions while using Flagyl ER

It is important that your doctor check your progress at regular visits to make sure that the infection is cleared up. Blood tests may be needed to check for unwanted effects.

If your symptoms do not improve within a few days after you start this medicine or if they become worse, check with your doctor.

Do not take metronidazole if you have taken disulfiram (Antabuse®) within the last 2 weeks. Using these medicines together may cause serious unwanted effects.

Drinking alcoholic beverages while using this medicine may cause stomach pain, nausea, vomiting, headache, or flushing or redness of the face. Other alcohol-containing preparations (eg, elixirs, cough syrups, tonics) may also cause problems. These problems may last for at least one day after you stop using metronidazole. This medicine may also cause alcoholic beverages to taste different. You should not drink alcoholic beverages or take other alcohol-containing preparations while you are using this medicine and for at least 3 days after stopping it.

If you have trichomoniasis: Using this medicine while you are pregnant (especially during the first 3 months of pregnancy) can harm your unborn baby. Use an effective form of birth control to keep from getting pregnant. If you think you have become pregnant while using the medicine, tell your doctor right away.

If you are using this medicine for trichomoniasis (an infection of the sex organs in men or women), your doctor may want to treat your sexual partner at the same time you are being treated, even if he or she has no symptoms. Also, it may be desirable to use a condom (rubber) during sexual intercourse. These measures will help to keep you from getting the infection back again from your partner. If you have any questions about this, talk with your doctor.

Check with your doctor right away if you have burning, numbness, tingling, or painful sensations in the arms, hands, legs, or feet. These could be symptoms of a condition called peripheral neuropathy.

Check with your doctor right away if you have dizziness, problems with muscle control or coordination, shakiness or an unsteady walk, slurred speech, or trouble speaking. These may be symptoms of a serious brain condition called encephalopathy.

Call your doctor right away if you have confusion, drowsiness, fever, a general feeling of illness, a headache, loss of appetite, nausea, a stiff neck or back, or vomiting. These could be symptoms of a serious condition called aseptic meningitis.

This medicine may increase your risk of having serious liver problems, which may be life-threatening. This is more likely if you have Cockayne syndrome (rare form of dwarfism). Check with your doctor right away if you have pain or tenderness in the upper stomach, pale stools, dark urine, loss of appetite, nausea, vomiting, or yellow eyes or skin.

Metronidazole may cause dry mouth, an unpleasant or sharp metallic taste, and a change in taste sensation. For temporary relief of dry mouth, use sugarless candy or gum, melt bits of ice in your mouth, or use a saliva substitute. If your mouth continues to feel dry for more than 2 weeks, check with your medical doctor or dentist. Continuing dryness of the mouth may increase the chance of dental disease, including tooth decay, gum disease, and fungus infections.

Serious skin reactions can occur with this medicine. Check with your doctor right away if you have blistering, peeling, or loosening of the skin, red skin lesions, severe acne or a skin rash, sores or ulcers on the skin, or fever or chills with this medicine.

Do not take other medicines unless they have been discussed with your doctor. This includes prescription or nonprescription (over-the-counter [OTC]) medicines and herbal or vitamin supplements.

## Flagyl ER side effects

Along with its needed effects, a medicine may cause some unwanted effects. Although not all of these side effects may occur, if they do occur they may need medical attention.

Check with your doctor immediately if any of the following side effects occur:

More common

- Agitation
- back pain
- blindness
- blurred vision
- burning, numbness, tingling, or painful sensations in the hands or feet
- changes in speech patterns
- confusion
- decreased vision
- depression
- dizziness
- drowsiness
- eye pain
- fever
- headache
- irritability
- lack of coordination
- nausea
- seeing or hearing things that are not there
- seizures
- shakiness and unsteady walk
- slurred speech
- stiff neck or back
- trouble speaking
- unsteadiness, trembling, or other problems with muscle control or coordination
- unusual tiredness or weakness
- vomiting
- weakness in the arms, hands, legs, or feet

Less common

- Black, tarry stools
- blood in the urine
- body aches or pain
- burning while urinating
- chills
- clumsiness or unsteadiness
- difficulty with breathing
- ear congestion
- fainting
- feeling of pelvic pressure
- frequent or painful urination
- irregular heartbeat
- loss of voice
- nasal congestion
- pinpoint red spots on the skin
- runny nose
- skin rash, hives, redness, itching
- sneezing
- stomach and back pain (severe)
- unusual bleeding or bruising
- vaginal irritation, discharge, or dryness not present before taking the medicine

Rare

- Bleeding gums
- bloating
- chest pain
- constipation
- cough
- dark urine
- fast heartbeat
- indigestion
- loss of appetite
- painful or difficult urination
- pains in the stomach, side, or abdomen, possibly radiating to the back
- sore throat
- sores, ulcers, or white spots on the lips or in the mouth
- swollen glands
- yellow eyes or skin

Incidence not known

- Blistering, peeling, or loosening of the skin
- bloody or cloudy urine
- burning while urinating
- continuing diarrhea
- continuing stomach pain
- diarrhea
- feeling of warmth
- increased volume of pale, dilute urine
- joint or muscle pain
- loss of bladder control
- red skin lesions, often with a purple center
- red, irritated eyes
- redness of the face, neck, arms, and occasionally, upper chest
- redness of the skin

Some side effects may occur that usually do not need medical attention. These side effects may go away during treatment as your body adjusts to the medicine. Also, your health care professional may be able to tell you about ways to prevent or reduce some of these side effects. Check with your health care professional if any of the following side effects continue or are bothersome or if you have any questions about them:

More common

- Dizziness or lightheadedness
- feeling of constant movement of self or surroundings
- heartburn
- sensation of spinning
- stomach cramps
- trouble sleeping
- weight loss

Rare

- Change in taste sensation
- congestion
- dry mouth
- pain or tenderness around the eyes and cheekbones
- tender, swollen glands in the neck
- trouble with swallowing
- unpleasant or sharp metallic taste
- voice changes

Incidence not known

- Decreased interest in sexual intercourse
- inability to have or keep an erection
- loss in sexual ability, desire, drive, or performance
- painful sexual intercourse

Other side effects not listed may also occur in some patients. If you notice any other effects, check with your healthcare professional.

Call your doctor for medical advice about side effects. You may report side effects to the FDA at 1-800-FDA-1088.

Flagyl ER side effects (more detail)

## Frequently asked questions

- What happens if you drink alcohol with metronidazole?
- How long does it take for metronidazole to work?
- How long does it take metronidazole to leave your system?
- Can metronidazole cause a yeast infection?
- Does metronidazole treat chlamydia?
- Can you have sex while taking metronidazole?
- Can you use Soolantra and metronidazole together?

## More about Flagyl ER (metronidazole)

- Check interactions
- Reviews (8)
- Drug images
- Side effects
- Dosage information
- During pregnancy
- Drug class: amebicides
- Breastfeeding

### Professional resources

- Prescribing Information

### Other formulations

- Flagyl
- Flagyl I.V. Intravenous
- Flagyl 375 Capsules

### Related treatment guides

- Bacterial Vaginosis
- STD Prophylaxis
- Balantidium coli
- Dientamoeba fragilis
- Nongonococcal Urethritis

## Further information

Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.

Medical Disclaimer