Metronidazole Oral Tablet

The metronidazole immediate-release tablet and extended-release tablet are prescription drugs. They’re both taken by mouth. These tablets are available as the brand-name drugs Flagyl (immediate-release) and Flagyl ER (extended-release).

These drugs are also available as generic drugs. Generic drugs usually cost less. In some cases, they may not be available in every strength or form as the brand-name version. 

Why it's used

Metronidazole immediate-release oral tablets are used to treat many infections caused by bacteria or parasites. These include infections that occur in the gastrointestinal tract or reproductive system. Metronidazole extended-release oral tablets are used to treat vaginal infections in women.

Metronidazole may be used as part of a combination therapy. This means you may need to take it with other medications.

How it works

Metronidazole belongs to a class of drugs called nitroimidazole antimicrobials. A class of drugs is a group of medications that work in a similar way. These drugs are often used to treat similar conditions. 

The metronidazole tablets work by killing bacteria. This relieves the infection.

Metronidazole oral tablet can interact with other medications, vitamins, or herbs you may be taking. An interaction is when a substance changes the way a drug works. This can be harmful or prevent the drug from working well.

To help avoid interactions, your doctor should manage all of your medications carefully. Be sure to tell your doctor about all medications, vitamins, or herbs you’re taking. To find out how this drug might interact with something else you’re taking, talk to your doctor or pharmacist.

Drugs you should not take with metronidazole

Disulfiram: Do not take disulfiram with metronidazole. Doing so can cause dangerous effects in your body. Using it with metronidazole can cause psychotic reactions. Symptoms can include:

• confusion
• hallucinations (seeing or hearing things that aren’t real)
• delusions (believing things that aren’t real)

Do not take metronidazole if you’ve taken disulfiram in the last two weeks.

Interactions that increase your risk of side effects

Taking metronidazole with certain medications raises your risk of side effects. This is because the amount of either drug may be increased in your body. Examples include:

Lithium: Increased side effects of metronidazole can include a higher risk of QT prolongation (irregular heartbeat).

Warfarin or other blood thinners: Increased side effects of these drugs include a higher risk of bleeding.

Busulfan: If possible, you should avoid taking busulfan with metronidazole. If you do take these drugs together, your doctor may check the amount of busulfan in your body more often.

Disclaimer: Our goal is to provide you with the most relevant and current information. However, because drugs interact differently in each person, we cannot guarantee that this information includes all possible interactions. This information is not a substitute for medical advice. Always speak with your healthcare provider about possible interactions with all prescription drugs, vitamins, herbs and supplements, and over-the-counter drugs that you are taking.

Metronidazole oral tablet is safe to use with hormonal birth control methods. While one type of antibiotic (rifampin) is known to cause problems with some birth control, it’s not an issue with metronidazole. No research shows that this drug can make you more likely to get pregnant if you’re using the pill or other types of hormonal birth control.

Of course, if you have concerns, be sure to ask your doctor. And you can always use a backup method of birth control, such as a condom, while you’re taking metronidazole. To learn more, check out this article, which gives more information about antibiotics and birth control.

Metronidazole oral tablet comes with several warnings.

Allergic reaction

Metronidazole can cause a severe allergic reaction or hypersensitivity. Symptoms can include:

• hives (itchy welts)
• red rash
• peeling or sloughing of your skin
• wheezing
• fever
• chills 

If you have an allergic reaction, call your doctor or local poison control center right away. If your symptoms are severe, call 911 or go to the nearest emergency room.

Don’t take this drug again if you’ve ever had an allergic reaction to it. In some cases, taking it again could lead to death.

Alcohol interaction

You should stop using drinks that contain alcohol at least three days before starting metronidazole. Also avoid alcohol for three more days after you stop treatment with this drug.

This is because alcohol can cause side effects when used with metronidazole. These include:

• nausea
• vomiting
• abdominal cramps
• headaches
• flushing (sudden redness and warmth in your face)

If you drink alcohol, talk to your doctor about whether this drug is safe for you.

Warnings for certain groups

For people with liver disease: Your liver helps process this drug. If you have severe liver disease, your liver may process this drug more slowly. This would increase the amount of the drug in your body and raise your risk of side effects. Your doctor may lower your dosage of metronidazole or have you take it less often.

For people with kidney disease: Your kidneys help clear this drug from your body. If you have severe kidney disease, your kidneys may process this drug more slowly. This increases the amount of the drug in your body and raises your risk of side effects. Your doctor may lower your dose of metronidazole or have you take it less often.

For pregnant women: Metronidazole is a category B pregnancy drug. That means two things:

• Studies of the drug in pregnant animals have not shown a risk to the fetus.
• There aren’t enough studies done in pregnant women to show if the drug poses a risk.

Talk to your doctor if you’re pregnant or planning to become pregnant. Metronidazole should not be taken during the first trimester of pregnancy. For the second and third trimesters, this drug should be used only if the potential benefit justifies the potential risk.

For women who are breastfeeding: Metronidazole may pass into breast milk and cause side effects in a child who is breastfed. Talk to your doctor if you breastfeed your child. You may need to decide whether to stop breastfeeding or stop taking this medication.

For seniors: The kidneys of older adults may not work as well as they used to. This can cause your body to process drugs more slowly. As a result, more of a drug stays in your body for a longer time. This increases your risk of side effects. 

Metronidazole tablets are used for short-term treatment. They come with risks if you don’t take them as prescribed.

If you stop taking the drug suddenly or don’t take it at all

Your infection may not improve, and may get worse.

If you miss doses or don’t take the drug on schedule

Your medication may not work as well or may stop working completely. For this drug to work well, a certain amount needs to be in your body at all times.

If you take too much

You could have dangerous levels of the drug in your body. If you think you’ve taken too much of this drug, call your doctor or local poison control center. If your symptoms are severe, call 911 or go to the nearest emergency room right away.

What to do if you miss a dose

Take your dose as soon as you remember. But if you remember just a few hours before your next scheduled dose, take only one dose. Never try to catch up by taking two doses at once. This could result in dangerous side effects.

How to tell if the drug is working

Your symptoms of infection should improve.