Metronidazole (Oral)

Available in various forms, Metronidazole is used to treat bacterial infections, such as H. pylori, endocarditis, clostridium difficile colitis and/or bacterial vaginosis.


When taken orally, Metronidazole acts as an antibiotic and an antiprotozoal agent. As well as treating bacterial infections, Metronidazole can, therefore, be used to resolve protozoan infections. Due to its effectiveness, Metronidazole can be prescribed to patients with various types of bacterial infections, including pelvic inflammatory disease, aspiration pneumonia, bacterial vaginosis, lung abscesses, pseudomembranous colitis, periodontitis, endocarditis, H. pylori, amebiasis, giardiasis trichomoniasis, oral and intra-abdominal infection, as well as mild-to-moderate clostridium difficile colitis.

Often, patients are treated with Metronidazole once the infection has been established and they are suffering from symptoms. However, Metronidazole may also be prescribed a prophylactic and given to patients prior to surgery in order to prevent an infection from developing.

As a nitromidazole antibiotic, Metronidazole works by inhibiting nucleic acid synthesis. In doing so, Metronidazole affects the DNA of microbial cells. Once this has happened, the cells are unable to replicate and the infection cannot spread further. In addition to this, Metronidazole induces cell death and enables the body to destroy existing bacteria cells.

Although Metronidazole is extremely effective in treating bacterial infections, it has a minimal impact on aerobic bacteria or human cells. By targeting only anaerobic cells, Metronidazole can treat the patient's infection whilst causing relatively little harm to other healthy cells.

As Metronidazole functions as an antibiotic, it is only effective in treating infections which have been caused by bacteria and should not be used to treat fungal or viral infections.

Whilst Metronidazole can cause a number of side effects and must be taken with caution, it is a first-line treatment for many infections. As the medication takes effect relatively quickly and is able to target bacteria cells, it can resolve most bacterial infections and relieve the patient's symptoms.

Conditions Treated

  • Bacterial infections

Type Of Medicine

  • Nitromidazole antibiotic

Side Effects

When patients are taking Metronidazole, it is not uncommon for them to experience some side effects. Even if patients do exhibit side effects when taking this medication, it does not mean that it will be ineffective in treating their infection. Whilst some side effects will require further medical treatments, others are likely to dissipate as the patient's body becomes accustomed to the medicine.

For example, patients may experience the following side effects when taking Metronidazole orally:

  • Stomach or abdominal cramps
  • Lightheadedness or dizziness
  • Feeling of constant movement of surroundings or self
  • Heartburn
  • Dry mouth
  • Sensation of spinning
  • Congestion
  • Trouble sleeping
  • Change in taste sensation
  • Trouble swallowing
  • Weight loss
  • Tenderness or pain around the cheekbones and eyes
  • Swollen, tender glands in the neck
  • Decreased interest in sexual intercourse
  • Voice changes
  • Sharp or unpleasant metallic taste
  • Inability to have or keep an erection
  • Painful sexual intercourse
  • Loss in sexual drive, desire, performance or ability

If the above side effects occur and are fairly mild, patients may not need further medical attention. However, if the patient suffers from severe or prolonged side effects when taking Metronidazole, medical advice should be sought.

Similarly, patients should notify a healthcare practitioner straight away if they develop the following side effects when taking Metronidazole:

  • Agitation
  • Stiff back or neck
  • Nausea
  • Back pain
  • Slurred speech
  • Blindness
  • Unsteadiness
  • Blurred vision
  • Shakiness
  • Tingling, painful, numbness, or burning sensations in the feet or hands
  • Changes in speech patterns
  • Lack of coordination
  • Confusion
  • Headache
  • Convulsions
  • Irritability
  • Decreased vision
  • Hallucinations
  • Depression
  • Trouble speaking
  • Dizziness
  • Trembling, unsteadiness or other problems with coordination or muscle control
  • Drowsiness
  • Unusual weakness or tiredness
  • Eye pain
  • Vomiting
  • Fever
  • Weakness in the feet, legs, hands or arms
  • Tarry, black stools
  • Ear congestion
  • Blood in the stools or urine
  • Unsteadiness or clumsiness
  • Body pains or aches
  • Difficulty with breathing
  • Chills
  • Loss of appetite
  • Feeling of pelvic pressure
  • Painful or difficult urination
  • Indigestion
  • Loss of voice
  • Dark colored urine
  • Nasal congestion
  • Cough
  • Red pinpoint spots on the skin
  • Constipation
  • Runny nose
  • Hives, itching or redness
  • Sneezing
  • Fast heartbeat
  • Rash on the skin
  • Bloating
  • Back and stomach pain (severe)
  • Pains in the chest
  • Unusual bruising or bleeding
  • Sore throat
  • Vaginal dryness, discharge, or irritation not present before taking the medicine
  • Burning while urinating
  • Diarrhea (may be continuing)
  • Swollen glands
  • Bleeding gums
  • Pains in the abdomen, side or stomach, possibly radiating to the back
  • White spots, ulcers or sores in the mouth or on the lips
  • Cloudy or bloody urine
  • Yellowing of the skin or eyes
  • Loosening, peeling or blistering of the skin
  • Continuing stomach pain
  • Muscle or joint pain
  • Redness of the skin
  • Feeling of warmth
  • Irritated, red eyes
  • Redness of the arms, neck face and, sometimes, the upper chest
  • Loss of bladder control
  • Increased volume of pale, dilute urine
  • Red skin lesions, sometimes with a purple center

Patients should also seek medical help if they experience any other side effects whilst using Metronidazole.


Before taking Metronidazole, patients should ensure that they understand the dosage instructions issued by their doctor. When patients are taking Metronidazole, their dose will depend on various factors, such as the type of infection they have, their age, weight, medical history and the type of medication they're given. Different doses may be given depending on whether the patient is prescribed standard Metronidazole tablets or extended-release tablets, for example.

If adult patients are being treated with standard Metronidazole tablets or capsules for amebiasis infections, for example, they are usually advised to take 500-700mg three times per day, for a period of five to ten days. Whilst pediatric patients may be prescribed Metronidazole for the same condition, their dose will be dependent on their weight. Generally, pediatric patients are prescribed 30-35mg of Metronidazole per kilogram of bodyweight, per day. However, this daily dose should be split into three equal doses and taken throughout the day, rather than as one single dose.

Similarly, standard Metronidazole tablets or capsules can be used to treat a variety of bacterial infections. In these cases, adult patients and teenagers are generally instructed to use 7.5mg of Metronidazole per kilogram of bodyweight, every six hours for seven to ten days. The patient's physician will calculate their dose based on their weight and tell them exactly how much Metronidazole to take at each dose.

If adults and/or teenagers are prescribed standard Metronidazole tablets for the treatment of trichomoniasis infections, the medication can be prescribed in different ways. Patients can be given a single dose of 2g, two doses of 1g or as 250mg three times per day, for a period of seven days. However, if patients are prescribed standard Metronidazole capsules, they are usually advised to take 375mg twice per day, for a period of seven days.

In some cases, extended-release Metronidazole tablets may be used to treat bacterial vaginosis. If so patients are usually prescribed 750mg, to be taken once per day for a period of seven days.

Although this is a standard treatment regime, every patient will be assessed individually and given specific dosage instructions. Patients should, therefore, follow their doctor's advice and take Metronidazole exactly as their doctor has told them to. Patients should continue to take Metronidazole for the full course of treatment, even if their symptoms have been relieved. If patients stop taking Metronidazole too early, their symptoms and infection are likely to return and may be more difficult to treat in the future.

Standard Metronidazole tablets or capsules can usually be taken with or without food. However, if patients experience stomach discomfort or upset when taking Metronidazole, they may find that their side effects are reduced if they take the medication with a snack or meal.

However, extended-release Metronidazole tablets should be taken at least one hour before eating or at least two hours after eating. Patients should also swallow the extended-release tablet whole and should not attempt to crush, chew or break it.

If patients are unable to take tablets or capsules, Metronidazole can also be prescribed as an oral solution.

Metronidazole works most effectively when there is a consistent amount of medication present in the patient's body. It is important that patients adhere to their dosing schedule, take the medication at regular times and do not miss any doses. If patients are advised to take more than one dose per day, each dose should be evenly spaced.

If patients forget to take a dose of Metronidazole, they should do so as soon as they remember to. However, if their next dose is due relatively soon, patients will need to skip the missed dose. Patients should not attempt to take an extra or double dose of Metronidazole, even if a previous dose has been missed.

If patients need assistance with taking Metronidazole or are unsure how to use their medication, they should contact their physician or pharmacist for advice.

Potential Drug Interactions

Although some medications can be taken at the same time, others are likely to interact if they are used in conjunction with one another. Due to this, Metronidazole should not be prescribed alongside the following medications:

  • Amifampridine
  • Pimozide
  • Amisulpride
  • Sparfloxacin
  • Amprenavir
  • Dronedarone
  • Bepridil
  • Terfenadine
  • Cisapride
  • Saquinavir
  • Disulfiram
  • Thioridazine
  • Dronabinol
  • Ziprasidone
  • Mesoridazine

Similarly, taking Metronidazole in conjunction with any of the following medicines it not usually recommended:

  • Alfuzosin
  • Amiodarone
  • Amitriptyline
  • Anagrelide
  • Apomorphine
  • Aripiprazole
  • Arsenic Trioxide
  • Asenapine
  • Mycophenolic Acid
  • Astemizole
  • Ofloxacin
  • Atazanavir
  • Nilotinib
  • Azithromycin
  • Norfloxacin
  • Bedaquiline
  • Octreotide
  • Bupropion
  • Olanzapine
  • Buserelin
  • Nelfinavir
  • Busulfan
  • Nafarelin
  • Capecitabine
  • Prochlorperazine
  • Chloroquine
  • Quetiapine
  • Chlorpromazine
  • Propafenone
  • Cholera Vaccine, Live
  • Quinidine
  • Ciprofloxacin
  • Promethazine
  • Citalopram
  • Protriptyline
  • Clarithromycin
  • Quinine
  • Clomipramine
  • Mebendazole
  • Clozapine
  • Mifepristone
  • Crizotinib
  • Mizolastine
  • Cyclobenzaprine
  • Moxifloxacin
  • Dabrafenib
  • Methadone
  • Dasatinib
  • Mefloquine
  • Degarelix
  • Paliperidone
  • Delamanid
  • Paroxetine
  • Desipramine
  • Pentamidine
  • Deslorelin
  • Pasireotide
  • Disopyramide
  • Panobinostat
  • Dofetilide
  • Pazopanib
  • Dolasetron
  • Ranolazine
  • Domperidone
  • Pimavanserin
  • Donepezil
  • Posaconazole
  • Doxepin
  • Pipamperone
  • Doxifluridine
  • Probucol
  • Droperidol
  • Ebastine
  • Pitolisant
  • Efavirenz
  • Perphenazine
  • Eribulin
  • Procainamide
  • Erythromycin
  • Solifenacin
  • Escitalopram
  • Sorafenib
  • Famotidine
  • Sunitinib
  • Felbamate
  • Sulpiride
  • Fingolimod
  • Tacrolimus
  • Flecainide
  • Tamoxifen
  • Fluconazole
  • Sotalol
  • Fluorouracil
  • Leuprolide
  • Fluoxetine
  • Levofloxacin
  • Formoterol
  • Lumefantrine
  • Foscarnet
  • Mycophenolate Mofetil
  • Fosphenytoin
  • Ondansetron
  • Galantamine
  • Lapatinib
  • Gatifloxacin
  • Tegafur
  • Tolterodine
  • Gemifloxacin
  • Telavancin
  • Gonadorelin
  • Tizanidine
  • Goserelin
  • Telithromycin
  • Granisetron
  • Telaprevir
  • Halofantrine
  • Tetrabenazine
  • Haloperidol
  • Toremifene
  • Histrelin
  • Vandetanib
  • Hydroquinidine
  • Trazodone
  • Hydroxychloroquine
  • Vardenafil
  • Hydroxyzine
  • Vemurafenib
  • Ibutilide
  • Trimipramine
  • Iloperidone
  • Triptorelin
  • Imipramine
  • Voriconazole
  • Itraconazole
  • Vinflunine
  • Ivabradine
  • Vilanterol
  • Sevoflurane
  • Ketoconazole
  • Sodium Phosphate, Dibasic
  • Perflutren Lipid Microsphere
  • Vorinostat
  • Sodium Phosphate
  • Rilpivirine
  • Venlafaxine
  • Sodium Phosphate, Monobasic
  • Risperidone
  • Zuclopenthixol
  • Ritonavir
  • Warfarin
  • Sertindole

In some cases, however, it may be necessary to treat the patient with Metronidazole and one of the medications listed above. If so, the patient may be given a modified dose of medicine or they may be advised to take their medications at specific times.

As Metronidazole can also interact with other substances, patients should not consume or drink the following when taking this medication:

  • Alcohol (Ethanol)

Due to the seriousness of the interaction between Metronidazole and alcohol, patients should not consume alcohol for at least 72 hours after taking their final dose of medication.

Patients should tell their physician if they are using any prescribed medicines, over-the-counter medications, supplements or vitamins before they take their first dose of Metronidazole. Patients will also need to obtain medical advice before using any new medicines, vitamins or supplements once they have started taking Metronidazole.


If patients have any other medical conditions, it may affect their treatment with Metronidazole. Due to this, patients should discuss their existing health and medical history with their physician before they start using Metronidazole. The following conditions may be particularly relevant if treatment with Metronidazole is being considered:

  • Liver disease
  • Bone marrow or blood problems
  • Kidney disease
  • Low white blood cells (Leukopenia)
  • Brain disease
  • Eye disease with vision changes (Optic Neuropathy)
  • Candida infection (Oral thrush or vaginal yeast infection)
  • Seizures
  • Nerve disease with tingling, numbness or pain (Peripheral neuropathy)

Currently, the effects of Metronidazole on pediatric patients have only been studied in relation to the treatment of amebiasis. Although Metronidazole may be prescribed to pediatric patients for the treatment of other infections, caution should be used.

Whilst Metronidazole may be prescribed to female teenage patients for the treatment of bacterial vaginosis, it should only be used after the start of menstruation.

Metronidazole may be used to treat geriatric patients but the dose of medication may need to be modified. If patients have age-related kidney or liver problems, for example, it may take longer for the medication to be metabolized and a lower dose may be required.

Once patients have completed a course of Metronidazole, they should have a further check-up with their physician. This is to ensure that the infection has been fully resolved and to confirm that no additional treatment is required.

Patients should not take Metronidazole if they have used Disulfiram within the last two weeks. If these medications are combined, they can cause serious side effects.

Consuming alcohol whilst taking Metronidazole can cause harmful side effects, such as:

  • Nausea
  • Stomach pain
  • Headache
  • Vomiting
  • Redness or flushing of the face

Due to this, patients should not drink or consume any alcohol whilst taking this medication and for at least 72 hours after taking their last dose. Patients should also avoid foods and other substances which may contain alcohol or ethanol, such as cough syrups, tonics or elixirs.

If patients are prescribed Metronidazole for the treatment of trichomoniasis, their physician may also want to treat their sexual partner, even if he or she is not currently showing any symptoms. Patients should also use condoms during sexual intercourse in order to ensure that the infection is not passed back and forth between them and their partner.

Patients may have an increased risk of developing peripheral neuropathy whilst taking Metronidazole and should notify their doctor immediately if they exhibit the following symptoms:

  • Numbness or painful sensations in the feet, legs, arms or hands
  • Tingling or burning sensations in the feet, legs, arms or hands

Patients could also develop a serious brain condition, known as encephalopathy whilst taking Metronidazole. If patients develop the following symptoms, they should obtain immediate medical treatment:

  • Problems with coordination or muscle control
  • Dizziness
  • Unsteady walk
  • Trouble speaking
  • Slurred speech
  • Shakiness

If patients experience the following symptoms whilst taking Metronidazole, it may indicate that they are suffering from aseptic meningitis and will require urgent medical treatment:

  • General feeling of illness
  • Fever
  • Drowsiness
  • Confusion
  • Headache
  • Nausea
  • Loss of appetite
  • Stiff back or neck

When taking Metronidazole, patients may experience a change in their taste, a dry mouth and/or a metallic or unpleasant taste. For temporarily relief, patients may want to chew gum or suck ice chips. A saliva substitute may also be used. If this side effect persists for two weeks after the patient has finished taking Metronidazole, they should notify their doctor and/or dentist. A persistent dry mouth can increase the risk of gum disease, fungal infections, tooth decay and other dental disease.

Although Metronidazole has been classed as a category B drug in terms of pregnancy, it is not known whether this medication can cause harm to an unborn fetus. However, Metronidazole can cross the placental barrier and could, therefore, harm an unborn fetus. Due to this, caution must be shown if Metronidazole is prescribed to pregnant patients.

In some cases, it may not be appropriate to treat pregnant patients with Metronidazole. If patients are being treated for trichomoniasis with Metronidazole, for example, it can cause harm to an unborn fetus, particularly if it is taken during the first trimester of pregnancy. Due to this, patients should use effective birth control whilst taking Metronidazole and until the medication is out of their system.

If patients become pregnant when taking Metronidazole for any condition, they should notify their physician straight away.

If patients are breastfeeding, they may be advised to stop whilst they are taking Metronidazole. If a nursing mother is taking Metronidazole, it can be excreted in breast milk and could cause harm to an infant. Due to this, patients may prefer to express their breast milk before they start taking Metronidazole. Patients should obtain medical advice before breastfeeding if they are taking Metronidazole.

In addition to this, patients should confirm with their doctor when it is safe for them to resume breastfeeding after they have finished treatment with this medication. Metronidazole can stay in the patient's system for some time after they have taken their final dose and patients should not, therefore, breastfeed as soon as they have finished taking Metronidazole.

Before patients begin using Metronidazole, they must inform their physician if they have any known allergies. This includes allergies to medicines, foods, animals, preservatives, dyes and other substances. In rare cases, patients may develop an allergic reaction whilst taking Metronidazole and, if so, they will require emergency medical assistance. An allergic reaction can include the following symptoms:

  • Hives
  • Difficulty breathing
  • Itching
  • Difficulty swallowing
  • Shortness of breath
  • Rash on the skin
  • Hoarseness
  • Swelling of the face, lips, tongue, throat, mouth or hands


When storing Metronidazole at home, patients should follow the manufacturer's instructions and the medication guide. It's important that Metronidazole is kept in a safe location, such as a locked medicine cabinet, so that children and/or pets cannot gain access to it.

In most cases, Metronidazole tablets and capsules can be kept at room temperature but should be stored in a closed container. If Metronidazole capsules or tablets are supplied in a blister pack, for example, they should only be removed when patients are ready to take their next dose of medication. Metronidazole should also be stored in a location which is not exposed to heat, light or moisture.

If patients are advised to stop taking Metronidazole or if their medication reaches its expiry date, patients should dispose of it carefully. Medicines, including Metronidazole, should not be thrown out with regular household waste as they may pose a risk to other people. Instead, patients should contact their physician's office or pharmacist and access a specialist medicine disposal service.


If patients are exhibiting signs of an infection, physicians will need to examine them and perform tests to determine whether their condition has been caused by a virus, fungus or bacteria. If necessary, additional tests may be carried out in order to find out exactly what type of bacteria, fungus or virus has caused the condition.

As Metronidazole is effective against various types of bacterial infections, it is a commonly used antibiotic. Although this medication can cause patients to experience a number of adverse effects, these are often short-lived and the benefits of treatment with Metronidazole often outweigh the risk of developing short-term side effects.