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Medically reviewed on October 4, 2017.
Medically reviewed on April 16, 2018.
What is Flagyl ER?
Flagyl ER is an antibiotic that fights bacteria.
Flagyl ER is used to treat bacterial infections of the vagina, stomach, liver, skin, joints, brain, and respiratory tract. This medication will not treat a vaginal yeast infection.
Flagyl ER may also be used for purposes not listed in this medication guide.
Do not drink alcohol or consume foods or medicines that contain propylene glycol while you are taking Flagyl ER and for at least 3 days after you stop taking it.
In animal studies, Flagyl ER caused certain types of cancers or tumors. It is not known whether these effects would occur in people using this medicine. Ask your doctor about your risk.
Before taking this medicine
You should not take Flagyl ER if you are allergic to it, or if you have taken disulfiram (Antabuse) within the past 2 weeks.
To make sure Flagyl ER is safe for you, tell your doctor if you have ever had:
a stomach or intestinal disease such as Crohn's disease;
a blood cell disorder such as anemia (lack of red blood cells) or low white blood cell (WBC) counts;
a fungal infection anywhere in your body; or
a nerve disorder.
In animal studies, Flagyl ER caused certain types of tumors, some of which were cancerous. However, very high doses are used in animal studies. It is not known whether these effects would occur in people using regular doses. Ask your doctor about your risk.
Using Flagyl ER during pregnancy could harm the unborn baby. Tell your doctor if you are pregnant or if you become pregnant while using this medicine.
Metronidazole can pass into breast milk and may harm a nursing baby. You should not breast-feed within 24 hours after using metronidazole. If you use a breast pump during this time, throw out any milk you collect. Do not feed it to your baby.
Do not give this medicine to a child without medical advice.
How should I take Flagyl ER?
Follow all directions on your prescription label. Do not take this medicine in larger or smaller amounts or for longer than recommended.
Shake the oral suspension (liquid) well just before you measure a dose. Measure liquid medicine with the dosing syringe provided, or with a special dose-measuring spoon or medicine cup. If you do not have a dose-measuring device, ask your pharmacist for one.
Do not crush, chew, or break an extended-release tablet. Swallow it whole.
If you are treating a vaginal infection, your sexual partner may also need to take Flagyl ER (even if no symptoms are present) or you could become reinfected.
Flagyl ER is usually given for up to 10 days in a row. You may need to repeat this dosage several weeks later.
Use this medicine for the full prescribed length of time. Your symptoms may improve before the infection is completely cleared. Skipping doses may also increase your risk of further infection that is resistant to antibiotics. Flagyl ER will not treat a viral infection such as the flu or a common cold.
Flagyl ER can cause unusual results with certain medical tests. Tell any doctor who treats you that you are using this medicine.
Store at room temperature away from moisture and heat.
What happens if I miss a dose?
Take the missed dose as soon as you remember. Skip the missed dose if it is almost time for your next scheduled dose. Do not take extra medicine to make up the missed dose.
What happens if I overdose?
Seek emergency medical attention or call the Poison Help line at 1-800-222-1222.
What should I avoid while taking Flagyl ER?
Do not drink alcohol or consume food or medicines that contain propylene glycol while you are taking Flagyl ER. You may have unpleasant side effects such as headaches, stomach cramps, nausea, vomiting, and flushing (warmth, redness, or tingly feeling). Also avoid alcohol or propylene glycol for at least 3 days after you stop taking this medicine.
Check the labels of any medicines or food products you use to make sure they do not contain alcohol or propylene glycol
Antibiotic medicines can cause diarrhea, which may be a sign of a new infection. If you have diarrhea that is watery or bloody, call your doctor. Do not use anti-diarrhea medicine unless your doctor tells you to.
Flagyl ER side effects
Get emergency medical help if you have signs of an allergic reaction: hives; difficult breathing; swelling of your face, lips, tongue, or throat.
Call your doctor at once if you have:
severe stomach pain, diarrhea that is watery or bloody;
trouble sleeping, depression, feeling irritable;
headache, dizziness, weakness;
a light-headed feeling (like you might pass out); or
blisters or ulcers in your mouth, red or swollen gums, trouble swallowing.
Stop taking the medicine and call your doctor right away if you have neurologic side effects (more likely to occur while taking Flagyl ER long term):
numbness, tingling, or burning pain in your hands or feet;
vision problems, pain behind your eyes, seeing flashes of light;
muscle weakness, problems with coordination;
trouble speaking or understanding what is said to you;
a seizure; or
fever, neck stiffness, and increased sensitivity to light.
Side effects may be more likely in older adults.
Common side effects may include:
nausea, vomiting, loss of appetite, stomach pain;
unpleasant metallic taste;
vaginal itching or discharge;
mouth sores; or
swollen, red, or "hairy" tongue.
This is not a complete list of side effects and others may occur. Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088.
See also: Side effects (in more detail)
What other drugs will affect Flagyl ER?
Sometimes it is not safe to use certain medications at the same time. Some drugs can affect your blood levels of other drugs you take, which may increase side effects or make the medications less effective.
Tell your doctor about all your current medicines and any you start or stop using, especially:
This list is not complete. Other drugs may interact with metronidazole, including prescription and over-the-counter medicines, vitamins, and herbal products. Not all possible interactions are listed in this medication guide.
Remember, keep this and all other medicines out of the reach of children, never share your medicines with others, and use this medication only for the indication prescribed.
Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.
Copyright 1996-2018 Cerner Multum, Inc. Version: 11.02.
More about Flagyl ER (metronidazole)
- Flagyl ER Side Effects
- During Pregnancy or Breastfeeding
- Dosage Information
- Drug Images
- Drug Interactions
- Support Group
- 6 Reviews – Add your own review/rating
- Generic Availability
- Drug class: amebicides