What Is Metronidazole Used For?
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Metronidazole - Uses, Dosage, Side Effects, Drug Warnings, and Precautions.

Published on Nov 15, 2022   -  6 min read


Metronidazole is a potent antibiotic used to treat various types of microbial infections. Through this article, learn more about its diverse benefits.


Metronidazole is an antibiotic widely prescribed to treat and prevent various conditions, including bacterial, viral, and other parasitic infections. It is also used to treat trichomoniasis (a sexually transmitted disease caused by a parasite, Trichomonas vaginalis). It is available as an oral tablet, extended-release tablet, immediate-release tablet, creams, gels, suppository, and IV solution for injection (to be given by a healthcare professional only). It acts by preventing the growth of the infection-causing organism. Do not consume alcohol or alcoholic products while on this medication. If any side effects are experienced while on Metronidazole, stop its use and seek emergency medical help.

Drug Group:

Metronidazole is an antiparasitic medication that belongs to the class of drugs called the nitroimidazoles, which is used to treat bacterial infections, and inflammations caused by members of the Rosaceae family amebiasis, giardiasis, trichomoniasis, and other parasitic infections. The other drugs of the nitroimidazole class include Tinidazole, Ornidazole, Nimorazole, etc.

What Is Metronidazole Used For?

Metronidazole is mainly used for parasitic infections caused by bacteria. The common infections caused by these bacteria are those in the skin, vagina, stomach, heart, lungs, and blood.

Metronidazole is also used in Crohn's disease to treat stomach ulcers caused by H.pylori. It is also employed to prevent bacterial infections post-surgery and is studied for its use in preventing the preterm birth of babies. Never take Metronidazole or any other medicine without consulting the physician first.

How Does Metronidazole Work?


Metronidazole acts by facilitating a process called passive diffusion in the cytoplasm of the bacteria. Thus, it diffuses into the bacterial body and binds with the bacteria's DNA (genetic material). This interaction will result in the inhibition of the synthesis of certain proteins which are required by the bacteria for its survival. Thus, Metronidazole directly has a destructive effect on the bacteria.

Onset of Action:

When orally administered, almost 90 to 100 % of the Metronidazole reaches the blood circulation. It reaches its maximum concentration in the blood within 20 to 180 minutes post-administration (the presence of food may delay this). Most of the drug is excreted via feces and urine, and almost 12 % is excreted in the urine in its unchanged form. In short, the onset of action for Metronidazole is between 20 to 180 minutes after oral administration. And the action may last up to 8-10 hours.


There have been no reports of habit-forming tendency in people taking Metronidazole.

Expiry Date:

Avoid taking this medicine after it expires. The expiry date and related details will be available on the back of the pack.

What Is the Dosage of Metronidazole?

Metronidazole dosing depends upon your body weight and the type of infection. The doctor may adjust the dose as required based on the response. Ensure to inform the doctor how well the drug works and if any side effects are experienced.

Metronidazole is available in 200mg, 250 mg, 375 mg, 500 mg and 750 mg oral tablets.


How to Use Metronidazole?

  1. Tablets: Swallow the medication as a whole after food.

  2. Liquid: Measure the right dose using a syringe or measure and take each dose, preferably after food.

  3. Suppository: Follow the instructions given on the package.

  4. Gel and Cream: Apply on the affected area and rub gently, as directed by the doctor.

Missed Dose:

Take this medication as soon as you remember if a dose is missed. If the next dose is near, skip the missed one and take the regular dosing regimen. Do not take two or double doses together.


In case of overdosing on the medication, contact the emergency department or the nearest poison control center immediately.

What Are the Contraindications of Metronidazole?

Do not use Mteronidazole in the following conditions:

  • A known allergy to the medication or any of its components.

  • Concomitant administration with alcohol or products containing Propylene Glycol.

  • Administration of drug Disulfiram with or within two weeks.

  • Cockayne syndrome (a genetic condition characterized by small head size, stature, and slow development).

  • First trimester (1 to12 week) of pregnancy.

What Are the Drug Warnings and Precautions?

Inform the doctor if any of these conditions are present:

  • Dermatologic: Topical cream use may cause skin irritation, necessitating withdrawal.

  • Metabolic: Caution is advised if on current therapy with corticosteroid drugs, those on a controlled sodium diet, or those predisposed to edema (swelling of face, limbs, etc.).

  • Liver Problems: Inform the doctor before starting medication, as the dose needs to be adjusted.

  • Kidney Diseases: Kidney diseases can slow down the excretion of the medication. Hence, inform the doctor before administration, as dose adjustments may be required.

  • Low Blood Cell Counts: Metronidazole may cause low blood counts. Hence, inform the doctor if the blood counts are low.

  • Pregnancy: Pregnant women with trichomoniasis vaginalis, regardless of the pregnancy stage, should be tested and assessed by their physician before starting the medication.

What Are the Side Effects of Metronidazole?

The common side effects of Metronidazole include

  • Unsteadiness or fainting.

  • Burning sensations in the chest and abdomen region are accompanied by a sense of being constantly in motion.

  • Difficulty sleeping.

  • Weight loss.

  • Pain or soreness around the eyes and cheekbones or a change in taste sensation.

  • Throat discomfort due to enlarged, painful neck glands and vocal alterations that are unpleasant or strongly metallic in flavor.

  • Seizures.

  • Slurred speech.

Most of the mild symptoms will go away in a few days. Alert the physician immediately if symptoms worsen or persist for more extended periods. In addition, Metronidazole causes other side effects not included here, so always seek medical advice for any questions.

What Are the Interactions of Metronidazole?

Drugs usually interact with other drugs, food, or supplements. These interactions must be considered and countered carefully to avoid unwanted side effects. The common interactions are listed below:

1. With Other Drugs:

  • Disulfiram: Avoid taking this medication if you have been on therapy with disulfiram within the last 14 days. Concomitant administration can lead to serious side effects that require medical attention.
  • Alfuzosin.

  • Amiodarone.

  • Amisulpride.

  • Bupropion.

  • Chlorpromazine.

  • Ciprofloxacin.

  • Clarithromycin.

  • Clomipramine.

  • Desipramine.

  • Donepezil.

  • Erythromycin.

  • Felbamate.

  • Fluconazole.

  • Fluorouracil.

  • Fluoxetin.

  • Fosphenytoin.

  • Gemifloxacin.

  • Haloperidol.

  • Levofloxacin.

  • Moxifloxacin.

  • Olanzapine.

  • Probucol.

  • Quetiapine.

  • Quinidine.

  • Sotalol.

  • Warfarin.

These are some of the significant interacting drugs with Metronidazole. Contact the physician or pharmacist to check for interactions before taking the drug with other drugs.

2. With Alcohol: The combination of Metronidazole with alcohol may cause nausea, vomiting, rapid heartbeat, and facial flushing. While using Metronidazole and for at least three days following the last dose, avoid alcohol completely.

3. With Diseases: Make sure to inform the doctor or pharmacist if there is a history of the following conditions:

  • Liver Diseases: Dose adjustment may be required.

  • Kidney Diseases: Delayed elimination of drug reported. It may require dose adjustment.

  • Low Blood Counts: Taking this medication may worsen these signs

  • Cockayne Syndrome: A rare genetic disorder.

What are the Common Brand Names or Trade Names of Metronidazole?

  • Tablet Aldezole 200 mg.

  • Tablet Flagyl 200 mg.

  • Tablet Metrogyl 200 mg.

  • Tablet Metron 200 mg.

  • Tablet Largyl 200 mg.

Frequently Asked Questions


What Conditions Does Metronidazole Treat?

The primary use of Metronidazole is for parasitic infections brought on by bacteria. These bacteria frequently cause infections in the skin, vagina, stomach, heart, lungs, and blood. 
In addition, Metronidazole is used to treat H. pylori (Helicbacter pylori)related stomach ulcers in patients with Crohn's disease. Additionally, it is used to stop bacterial infections after surgery, and its effectiveness in preventing premature delivery of children is being researched. Never administer Metronidazole or any other medication without first seeking medical advice.


Is Metronidazole a Reliable Antibiotic?

One of the primary medications for the treatment of protozoal infections, anaerobic bacterial infections, and microaerophilic bacterial infections is Metronidazole. Metronidazole is cytotoxic to microorganisms that are facultatively anaerobic. For viral infections, it is ineffective (such as the common cold, and flu).


When Should One Take Metronidazole?

One can take the capsules with or without food. It is preferable to take the medication with food or a snack if it disturbs the stomach. It is necessary to take the extended-release pill without meals, either one hour before or two hours after eating.


Is Metronidazole an Antibiotic for First-Line Use?

For mild to moderate Clostridium difficile infections, Metronidazole is used as the first line of therapy. Although 70 % of patients react to Metronidazole after five days, a 10 to 14-day regimen is advised because 91 % respond after a 14-day period. If oral therapy is ineffective, Metronidazole might be administered intravenously.


What Metronidazole Side Effects Are There?

The common side effects of Metronidazole are
- Dizziness. 
- There are burning feelings in the chest and belly.
- Inability to sleep. 
- Loss of weight. 
- An altered sense of taste or discomfort near the eyes and cheekbones. 
- Throat discomfort is brought on by swollen, uncomfortable neck glands and unpleasant or severely metallic-tasting voice changes. 
- Seizures. 
- Disoriented speech.


Which Bacteria Is Metronidazole Effective?

Metronidazole has been authorized as a successful treatment against Protozoa such as Entamoeba histolytica, Giardia lamblia, and Trichomonas vaginalis. Apart from that Metronidazole is extremely sensitive to gram-negative anaerobes such as Bacteroides and Fusobacterium.


Is Metronidazole a Better Option Than Amoxicillin?

Both Metronidazole and Amoxicillin are effective antibiotics. A total of 350 reviews for Amoxicillin have been submitted to Drugs.com, with an average rating of 6.3 out of 10. 32 % of reviewers noted a negative effect, compared to 52 % who noted a favorable effect. According to a survey in an online platform, Metronidazole has received a total of 2369 ratings, with an average rating of 6.1 out of 10.


In whom should metronidazole not be used?

Metrozone cannot be used by some individuals, such as those with a history of certain blood problems, Cockayne syndrome, Crohn's disease, epilepsy, or nerve abnormalities. A vaginal yeast infection cannot be treated with Metronidazole. Not advised to women nursing a baby or while pregnant.


Is Metronidazole a fungal medication?

Women with vaginal infections are treated with Metronidazole vaginal (eg, bacterial vaginosis). Metronidazole falls under the antibiotic drug subclass of medications. It functions by either eliminating the germs or halting their development. However, this medication will not treat yeast infections or vaginal fungal infections.


Are Loose Motions Treated with Metronidazole?

According to researchers, Metronidazole was effective in 76% of non-specific diarrhea in adult rhesus macaques (a species of monkey). Oral administration of Metronidazole at high daily doses of 500 to 1,500 mg for one to four days or at low daily doses of 250 mg for at least eight days produced effective therapy.


Does Metronidazole Kill Beneficial Bacteria?

While Metronidazole is successful in eliminating the harmful microorganisms that cause infections, it may also kill beneficial microorganisms that ordinarily exist in the vagina. Yeast overgrowth and disturbance of the vaginal environment may result from this.


Which Antibiotic Treats Diarrhea the Best?

Azithromycin is now the first-line antibiotic of choice for treating acute watery diarrhea (500 mg single dose), febrile diarrhea, and dysentery (single dose).


Can One Take Metronidazole for an Upset Stomach?

It is well known that the adverse effects of Metronidazole might ruin an individual's appetite and disturb the stomachs. The unpleasant taste alone can cause nausea and even vomiting in many people. Additionally, indigestion, diarrhea, and constipation might happen. It is enough to cause some people to completely quit their therapy. Always consult the physician in case of any trouble. To assist and prevent an upset stomach, the regular release pills can be taken with a meal, a snack, or a glass of milk.

Last reviewed at:
15 Nov 2022  -  6 min read




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