Metronidazole: What is it? Functions, Side Effects, Interactions and Dosing

It is antibiotic and antiparasitic of the group of nitroimidazoles.

It is a drug prescribed by a medical specialist to fight bacteria, parasites, or vaginaland gastrointestinal infections, especially the Trichomonas parasite, which causes a sexually transmitted disease called trichomoniasis.

This medicine acts by placing itself in the cells of the microorganisms belonging to the bacterium causing its disappearance when producing free radicals and preventing the synthesis of nucleic acids.

Metronidazole can be used as part of combination therapy.

Functions of Metronidazole

Metronidazole works by killing the bacteria. This relieves the infection.

Most common side effects

It is not usual for this medication to generate side effects; however, they may present:

  • Headache.
  • Loss of appetite
  • Nausea or vomiting
  • Diarrhea.
  • Heartburn.
  • Cramps in the stomach area.
  • Constipation.

If these effects are mild, they may disappear in a few days. Talk to your treating doctor or pharmacist if they are more severe or do not go away.


Side effects of grander scale:

You should contact a medical specialist if you experience severe side effects such as:

  • Problems in the nervous system, including seizures and encephalopathy.
  • Convulsions
  • Dizziness.
  • Headache.
  • Confusion.
  • Ataxia (loss of control of body movements).
  • Meningitis (inflammation in the brain).
  • Peripheral neuropathy (damage to the nerves in the hands and feet).
  • Memory loss.
  • Problems to focus on.
  • Fever.
  • Neck stiffness.
  • Numbness in your hands or feet.

There are not enough studies on pregnant women to show if the medication represents a risk.

If you want to be pregnant and should be treated with this medicine, consult your treating doctor.

Metronidazole should not be taken during the first trimester of pregnancy. For the second and third trimesters, this medication should be used only if the potential benefit justifies the potential risk.

For breastfeeding women: Metronidazole can pass into breast milk and cause side effects in a breastfed child. You may have to decide whether to stop breastfeeding or stop taking this medication.

In the elderly: the kidneys of older adults do not work with the same regularity as in the first years of life. This can cause your body to process drugs more slowly.

As a result, more than one medication stays in your body longer, which increases the risk of side effects.

For people with liver disease: your liver helps to process this medication.

If you have severe liver disease, your liver can process this medication more slowly. This would increase the number of drugs in your body and increase your risk of side effects.

For people with kidney disease: your kidneys help eliminate this medication from your body.

If you have severe kidney disease, your kidneys can process this medication more slowly. This increases the amount of medication in your body and increases the risk of side effects.

Drugs you should not take with Metronidazole.

Taking Metronidazole with certain medications increases the risk of side effects. This is because the amount of any of the medications can increase in the body, such as:

Disulfiram: Do not take disulfiram with Metronidazole. Doing so can cause dangerous effects on your body. The use of Metronidazole can cause psychotic reactions. Symptoms may include:

  • Confusion.
  • Hallucinations (seeing or hearing things that are not real).
  • Delusions (believe things that are not real).

Lithium: increased side effects of Metronidazole may include an increased risk of QT interval prolongation (irregular heartbeat).

Warfarin or other anticoagulants: the increased side effects of these medications include an increased risk of bleeding.

Allergic reaction to Metronidazole

It can cause a severe allergic reaction or hypersensitivity. The symptoms can be:

  • Hives with itching.
  • Red rash
  • Detachment of the skin.
  • Fever.
  • Cold.

Do not retake this medication if you have ever had an allergic reaction.

Interaction with alcohol

If your doctor prescribes taking this medication, you can not drink alcoholic beverages at least three days before starting treatment. Also, avoid alcohol for three more days after stopping the dose of Metronidazole.

This is because alcohol can cause side effects when mixed with this drug, such as:

  • Nausea.
  • Vomiting
  • Abdominal cramps.
  • Headaches.
  • Redness


Dosage for adults (between 18 and 64 years old):

Bacterial infections:

  • Typical dose: 500 mg four times a day.
  • Maximum dose: 4 g per day.

Amoebic infections:

  • Typical dose: 750 mg daily for 5-10 days.
  • Maximum dose: 4 g per day.


  • Typical dose: 2 grams (g) once a day, 1 g twice a day, or 250 milligrams three times a day. The treatment for this disease lasts seven days.
  • Maximum dose: 4 g per day.

Dosage for children (ages 0-17 years):

Amoebic infections:

  • Typical dose: 35-50 mg/kg of body weight per day administered in three divided doses for ten days.
  • Maximum dose: 2,250 mg per day.


  • Typical dose: 15 mg / kg of body weight per day administered in three doses for seven days.
  • Maximum dose: 1,000 mg per day.

Adult women (between 18 and 64 years old):

Vaginosis bacteriana:

  • Typical dose: 750 mg per day.
  • Maximum dose: 4 g per day.