Metronidazole: Dosage, Side Effects and Interaction

Generic Name: Metronidazole

Form: Oral immediate – release tablet

Brand: Flagyl


What is Metronidazole?

Metronidazole is an antibiotic which fights the bacteria or parasites in the body. It is used to treat various bacterial infections such as infections of the vagina, respiratory tract, stomach, joints and skin. Metronidazole belongs to a class of drugs which is called as nitiroimidazole antimicrobials. Group of medications that work in a similar way are called class of drugs. All drugs falling under the same class are often used to treat similar conditions.

Certain things to inform the doctor before taking the medicine 

  • One should not take this medication if there are any certainties of allergic reaction.
  • Pregnant ladies specially in the first trimester should inform the doctor about the pregnancy or if they are planning for pregnancy
  • Apart from metronidazole, if you are allergic to any other drugs
  • If you have any liver disease, stomach or intestinal disease
  • Convulsions or seizures
  • Nerve disorders
  • Any type of blood disorder
  • Metronidazole also passes in the breast milk which may harm the nursing baby. Hence lactating mothers should also inform the doctor of the same.

The doctor will check for the correct dose prescription keeping in mind the above issues or would suggest for certain tests ensuring the safety.

Metronidazole Dosage and Storage 

This medicine should be taken exactly as prescribed by the doctor or directions mentioned in the prescription label. Do not alter the dose limits i.e. do not take it in larger or smaller amounts without doctor’s permission. This medicine should not be taken for longer durations than recommended.

Swallow this medicine as whole. Do not crush, chew or break open the extended release tablet. The extended release tablet should be taken on an empty stomach or at least one hour before the meal else it should be taken two hours after the meal. Metronidazole should be taken for the duration as mentioned by the doctor even if you feel that the symptoms are now getting better. Skipping any of the doses can increase the risk of further infection that is resistant to antibiotics. Store metronidazole at room temperature, away from moisture and heat.

Metronidazole immediate release drugs get release in the body right away however the extended release drugs are slowly release over time.

Dosage for adults:

Bacterial Infections: Typical dose is 500mg which should be taken 4 time a day

Amoebic Infections: Typical dose is 750mg which should be taken 3 times a day for 5 to 10 days.

Dosage for Child:

Amoebic Infections: Typical dose is 35 to 50mg per day which is given in three divided doses to be taken for 10 days.

Dosage for Senior Citizens:

Since the kidneys of senior citizens may not work well as they used to earlier. Hence it would take time for the drug to process. As a result, more of the drug stays in the body for longer time which again increases the risk of side effects. Thus the doctor would start on a lower dose or different medication schedule.

Metronidazole does not treat viral flu or common cold. If you are conducting any tests inform your doctor beforehand that you are using metronidazole since this medication can deviate the results with certain medical tests.

If you miss the dose, take the missed dose as soon as you remember. However, if it is almost time for your next dose then it is better to skip the missed dose. Do not take extra medicine.

Seek medical help immediately if you overdose. Symptoms related to over dose are dizziness, nausea, tingling sensation, seizures, lack of coordination.

Side effects of Metronidazole 

Below major side effects should be reported to the doctor immediately:

  • Problems in vision or pain behind your eyes
  • Pain or burning sensation when you urinate
  • One may find trouble concentrating
  • Mood changes or behavioural changes
  • Confusion, sore throat, neck stiffness
  • Diarrhoea which is watery or bloody
  • Tingling sensation in the hands or legs
  • Sores inside the mouth or on the lips
  • Skin blisters, severe skin reaction

Minor side effects associated with metronidazole are:

  • Dizziness
  • Loss of balance
  • Itching in the vagina or vaginal discharge
  • Tongue getting sore or swollen
  • Dryness in the mouth
  • Runny nose or cough
  • Loss of appetite
  • Heartburn
  • Constipation

Few of the side effects are mild and go away within a few days however if the side effects are severe and stay for longer duration then inform the doctor rather than abruptly stopping the medication.

Drug interactions 

Metronidazole can interact with other drugs, herbal medicines, vitamins you may be already taking. Such interactions can be harmful or prevent the drug from working the way it is supposed to work.

If you are already taking any of the below medicines inform the doctor before being prescribed for metronidazole:

  • Lithium
  • Medication for convulsion such as phenobarbital or phenytoin
  • Cimetidine
  • Disulfiram
  • Blood thinners such as warfarin

Apart from drug interaction, metronidazole also causes alcohol interaction. At least three days before starting metronidazole stop intake of alcohol. Also avoid alcohol for three days once you stop the treatment. There are serious side effects associated with alcohol and metronidazole intake at the same time. Those are severe headaches, abdominal cramps, nausea, vomiting, loss of coordination, dizziness.


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