Flagyl Dosages for Adults and Kids: Your GoodRx Guide

Flagyl (metronidazole) is a common antibiotic that’s available with a prescription. It can treat several bacterial infections that affect the skin or gastrointestinal (GI) tract. And unlike many other antibiotics, it can even treat some infections caused by parasites.

Flagyl treats these infections through its nitroimidazole antibiotic effects. It works by breaking apart the DNA of infection-causing bacteria and parasites. This puts a halt to the growth and spread of infection.

In order to work at its best, you’ll need to take an optimal Flagyl dosage. You can take it as a 250 mg tablet, 375 mg capsule, or a 500 mg tablet. Flagyl also comes in several other formulations, such as an intravenous (IV) injection, vaginal gel, and a topical lotion.

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What’s the typical Flagyl dosage for adults?

The typical Flagyl dosage for adults depends on what type of infection you’re being treated for. Other health conditions you have, such as liver problems, can also impact your dose.

Bacterial (anaerobic) infections

Flagyl specializes in treating bacterial infections caused by anaerobic bacteria. These are a type of bacteria that can survive without oxygen. Anaerobic bacteria are often found in places like the mouth, gut, and soft tissue.

Your body weight can help determine what dose you’ll need. The typical adult Flagyl dosage for anaerobic bacterial infections is 7.5 mg per kilogram body weight 4 times a day. For an adult weighing 70 kg (154 lbs), this means the recommended Flagyl dose would be 500 mg by mouth 4 times a day for 7 to 10 days. The maximum dose in a 24-hour period is 4,000 mg.

This timeframe isn’t set in stone, either. More complicated infections — such as brain abscesses and complications from Crohn’s disease — may require longer treatment past 10 days. And in other cases, you may be told to take Flagyl only 2 or 3 times per day.

Trichomoniasis

Trichomoniasis is a sexually transmitted infection (STI) caused by a parasite called Trichomonas vaginalis.

The recommended Flagyl dosage for trichomoniasis can vary by sex:

• Women: Women usually take Flagyl for 1 day or 7 days. For a 1-day treatment course, the recommended Flagyl dosage is 2,000 mg by mouth as a single dose. You can also split it up and take 1,000 mg in the morning and 1,000 mg in the evening. For a 7-day treatment course, the recommended Flagyl dosage is 500 mg by mouth 2 times a day. Taking 250 mg by mouth 3 times per day is another option.

• Men: The recommended Flagyl dosage for men is 2,000 mg by mouth as a single dose. As an alternative, men can also take 250 mg by mouth 3 times a day for 7 days.

Amebiasis

Amebiasis is a GI infection caused by the parasite Entamoeba histolytica. It can cause symptoms like diarrhea, nausea, and weight loss. The recommended Flagyl dosage for amebiasis in adults is 500 mg to 750 mg by mouth 3 times a day for 5 to 10 days.

Helicobacter pylori infection

Helicobacter pylori (“H. pylori”) is another bacteria that can cause GI infections. There are many ways to treat H. pylori infections in adults. 

One mainstay treatment is a trio of three medications: Flagyl, clarithromycin (Biaxin XL), and a proton pump inhibitor like Prilosec (omeprazole). Of these, Flagyl is taken at a dose of 500 mg 3 times daily for 14 days (2 weeks). The other two medicines are taken twice daily for 14 days. 

What’s the typical Flagyl dosage for children?

Flagyl dosages for children are usually based on your child’s body weight in kilograms.

Amebiasis

To treat amebiasis in children, the typical Flagyl dosage is 35 mg to 50 mg per kilogram body weight. This is divided into smaller doses that are given 3 times a day for 7 to 10 days.

For example, if your child weighs 43 kg (95 lbs), a recommended daily dose might be 1,500 mg. This could be divided into 500 mg doses given in the morning, afternoon, and at bedtime.

A single dose shouldn’t exceed 750 mg, and a total daily dose shouldn’t be more than 2,250 mg.

Clostridioides difficile infection

Clostridioides difficile (“C. diff”) is a bacteria that causes infections in the colon. It can cause severe watery diarrhea, fever, and stomach cramping. Flagyl is a possible treatment for C. diff infection in infants and children.

The typical Flagyl dosage in this case is 7.5 mg per kilogram body weight 3 or 4 times a day for 10 days. A single dose shouldn’t exceed 500 mg.

Helicobacter pylori infection

The recommended H. pylori treatment for children is a combination of Flagyl, amoxicillin, and a proton pump inhibitor, such as Prilosec. They’ll likely take them for 14 days altogether.

Are there any dosage adjustments for medical conditions?

Yes. Flagyl dosage adjustments are recommended for certain people with liver problems. Your prescription may also be adjusted if you’re taking an interacting medication.

Dosage for people with liver problems

If you have liver problems, your healthcare provider will determine your Flagyl dose based on your liver health. They’ll figure this out by looking at your bloodwork results.

If you have mild or moderate liver problems, you shouldn’t need a dosage adjustment. But if your liver problems are more severe, your healthcare provider will likely recommend lowering your Flagyl dosage by half.

Why is this necessary? Your liver is responsible for breaking down (metabolizing) Flagyl after it enters your body. If your liver isn’t functioning properly, the medication may stay in your system for too long. This can raise your risk for new or worsening side effects.

Drug interactions

Flagyl can interact with several medications, most notably with disulfiram, warfarin, and lithium.

• Disulfiram is a medication that treats alcohol use disorder. If you combine it with Flagyl, it can cause hallucinations or an altered mental state. You shouldn’t take Flagyl with disulfiram.

• Warfarin (Coumadin, Jantoven) is a common blood thinner. Taking warfarin with Flagyl can raise your risk of bleeding. The combination should be used with caution.

• Lithium, a medication for bipolar disorder, should also be used with caution with Flagyl. The combination could raise your lithium level and lead to lithium toxicity. Symptoms of lithium toxicity can include tremors, blurry vision, and confusion.

This isn’t a complete list of interactions. Let your healthcare provider and pharmacist know about all other medications and supplements you’re taking. They can check if any interactions are present. They can also adjust your dose when needed.

Flagyl-alcohol interaction

Flagyl can cause a severe interaction with alcoholic beverages and other alcohol-containing products. If you drink alcohol while taking Flagyl, it’s possible to develop severe nausea, vomiting, and stomach cramps.

You should avoid drinking alcohol while taking Flagyl to prevent this from happening. It’s also a good idea to avoid alcohol for at least 3 days after your last dose.

What happens if you miss a dose of Flagyl?

If you miss a dose of Flagyl, you should take it as soon as you remember. But if it's close to your next scheduled dose, don’t take the missed dose. You should skip the missed dose and wait to take the next dose at your regular scheduled time.

Don’t double up on doses, either. Taking too many doses at one time can lead to extra Flagyl side effects.

What should you do if you take too much Flagyl?

If you take one or two extra doses of Flagyl, you may be at risk for experiencing more Flagyl side effects. Nausea, vomiting, and weakness are common examples. It can also cause more serious side effects when taken at very high doses for several days. Seizures and peripheral neuropathy (pain or weakness from nerve damage) have been reported.

If you think you’ve taken too much Flagyl, call your healthcare provider as soon as you can. If they’re not available, contacting Poison Control online or at 1-800-222-1222 is another option. They can walk you through the situation and recommend next steps.

However, if you’re experiencing symptoms that feel severe, it’s best to call 911 or seek emergency care immediately.

How to save on Flagyl

There are ways to save on Flagyl, which is available as both a brand-name and generic medication. GoodRx can help you save over 50% off the average retail price of the generic version. 

Generic metronidazole’s price at certain pharmacies is as low as $5.33 with a free GoodRx discount. Brand-name Flagyl is as low as $13.65.

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Written by:

Sonja Jacobsen, PharmD, BCPS, BCOP

Sonja Jacobsen, PharmD, BCPS, BCOP,  is a clinical oncology pharmacy specialist currently practicing in Seattle. She has been practicing as a pharmacist since 2015 and is licensed to practice in Washington state and North Carolina.

Edited by:

Joshua Murdock, PharmD, BCBBS

Joshua Murdock, PharmD, BCBBS, is a licensed pharmacist in Arizona, Colorado, and Rhode Island. He has worked in the pharmacy industry for more than 10 years and currently serves as a pharmacy editor for GoodRx.

Reviewed by:

Christina Aungst, PharmD

Christina Aungst, PharmD, is a pharmacy editor for GoodRx. She began writing for GoodRx Health in 2019, transitioning from freelance writer to editor in 2021.

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