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Metronidazole (oral/injection)

Generic Name: metronidazole (oral/injection) (me troe NI da zole)
Brand Name: FIRST Metronidazole, Flagyl, ...show all 9 brand names
Dosage Forms: intravenous solution (500 mg/100 mL); oral capsule (375 mg); oral suspension (100 mg/mL; 50 mg/mL); oral tablet (250 mg; 500 mg); oral tablet, extended release (750 mg)

What is metronidazole?

Metronidazole is an antibiotic that is used to treat bacterial infections of the vagina, stomach, liver, skin, joints, brain and spinal cord, lungs, heart, or bloodstream.

Metronidazole is also used to treat trichomoniasis, a sexually transmitted disease caused by a parasite. Usually both sexual partners are treated at the same time, even if one has no symptoms.

Do not use metronidazole to treat any condition that has not been checked by your doctor.

Metronidazole may also be used for purposes not listed in this medication guide.

Warnings

You should not use metronidazole if you recently drank alcohol, or have taken disulfiram (Antabuse) within the past 2 weeks.

Do not use metronidazole to treat any condition that has not been checked by your doctor.

Do not drink alcohol or consume foods or medicines that contain propylene glycol while you are taking metronidazole and for at least 3 days after you stop taking it.

Before taking this medicine

You should not use metronidazole if you are allergic to metronidazole, secnidazole, or tinidazole, or if:

  • you recently drank alcohol; or

  • you took disulfiram (Antabuse) within the past 14 days.

Do not take metronidazole during the first trimester of pregnancy. This medicine can harm an unborn baby. Tell your doctor if you are pregnant.

Tell your doctor if you have ever had:

  • liver disease;

  • kidney disease (or if you are on dialysis);

  • a heart rhythm disorder;

  • Cockayne syndrome (a rare genetic disorder);

  • 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, metronidazole caused certain types of tumors, some of which were cancerous. However, it is not known whether these effects would occur in humans. Ask your doctor about your risk.

You should not breastfeed 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.

Metronidazole is not approved for use in children younger than 12 years old, or in girls who have not begun having menstrual periods.

How should I take metronidazole?

Follow all directions on your prescription label and read all medication guides or instruction sheets. Use the medicine exactly as directed.

Metronidazole oral is taken by mouth.

Metronidazole injection is given as an infusion into a vein. A healthcare provider will give you this injection if you are unable to take the medicine by mouth.

Shake the oral suspension (liquid) before you measure a dose. Use the dosing syringe provided, or use a medicine dose-measuring device (not a kitchen spoon).

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 metronidazole so you don't become reinfected.

Metronidazole 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, even if your symptoms quickly improve. Skipping doses can increase your risk of infection that is resistant to medication. Metronidazole will not treat a viral infection such as the flu or a common cold.

Do not share this medicine with another person, even if they have the same symptoms you have.

This medicine can affect the results of certain medical tests. Tell any doctor who treats you that you are using metronidazole.

Metronidazole will not treat a vaginal yeast infection. You may even develop a new vaginal yeast infection, which may need to be treated with antifungal medication. Tell your doctor if you have symptoms such as itching or discharge during or after treatment with metronidazole.

Store at room temperature away from moisture and heat.

What happens if I miss a dose?

Take the medicine as soon as you can, but skip the missed dose if it is almost time for your next dose. Do not take two doses at one time.

What happens if I overdose?

Seek emergency medical attention or call the Poison Help line at 1-800-222-1222.

Overdose symptoms may include nausea, vomiting, and loss of balance or coordination.

What should I avoid while taking metronidazole?

While you are taking metronidazole and for 3 days after your last dose: Avoid drinking alcohol or consuming foods or other products that contain alcohol or propylene glycol. Drinking alcohol may cause unpleasant effects such as headaches, nausea, vomiting, stomach cramps, and warmth or tingling under your skin.

Metronidazole side effects

Get emergency medical help if you have signs of an allergic reaction (hives, itching, warmth or tingling; fever, joint pain; dry mouth, dry vagina; stuffy nose, difficult breathing, swelling in your face or throat) or a severe skin reaction (fever, sore throat, burning eyes, skin pain, red or purple skin rash with blistering and peeling).

Call your doctor at once if you have:

  • new or worsening symptoms of infection;

  • painful or difficult urination;

  • confusion;

  • 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 metronidazole 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 speech or coordination;

  • trouble speaking or understanding what is said to you;

  • a seizure; or

  • fever, neck stiffness, and increased sensitivity to light.

Metronidazole can cause life-threatening liver problems in people with Cockayne syndrome. If you have this condition, stop taking metronidazole and contact your doctor if you have signs of liver failure--nausea, stomach pain (upper right side), dark urine, clay-colored stools, or jaundice (yellowing of the skin or eyes).

Side effects may be more likely in older adults.

Common side effects may include:

  • depression, trouble sleeping, feeling irritable;

  • headache, dizziness, weakness;

  • nausea, vomiting, loss of appetite, stomach pain;

  • diarrhea, constipation;

  • unpleasant metallic taste;

  • rash, itching;

  • vaginal itching or discharge, pain during sex;

  • 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.

What other drugs will affect metronidazole?

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. Many drugs can affect metronidazole, especially:

  • an antidepressant;

  • asthma medication;

  • cancer medicine;

  • heart or blood pressure medication;

  • lithium or other antipsychotic medicine;

  • medicine to treat malaria, HIV, or other infection; or

  • a blood thinner--warfarin, Coumadin, Jantoven.

This list is not complete and many other drugs may affect metronidazole. This includes prescription and over-the-counter medicines, vitamins, and herbal products. Not all possible drug interactions are listed here.

Frequently asked questions

Further information

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.