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Metronidazole is an antibiotic and anti-parasitic drug that is commonly used to treat various infections caused by anaerobic bacteria and certain protozoans.

Last Modified: 09 May 2024

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What is Metronidazole? 

Metronidazole is an antibiotic and anti-parasitic drug that is commonly used to treat various infections caused by anaerobic bacteria and certain protozoans. The drug belongs to a class of medications known as nitroimidazoles and works by inhibiting the nucleic acid synthesis of microbial DNA. 

Metronidazole has a chemical structure that includes a nitroimidazole ring, which is crucial for its antimicrobial activity. It is synthesized through a series of chemical reactions that build the nitroimidazole moiety and attach necessary functional groups to achieve its active form. 

Global Name

Generic name: Metronidazole
Brand name: Flagyl, MetroGel, MetroCream, MetroLotion, and Noritate among others. 


What is Metronidazole used for? 

Metronidazole is used to treat a variety of infections, including: 

  • Bacterial vaginosis 
  • Trichomoniasis 
  • Amoebiasis 
  • Giardiasis 
  • Infections caused by Clostridium difficile 
  • Anaerobic bacterial infections such as intra-abdominal infections, skin and skin structure infections, and gynecologic infections such as pelvic inflammatory disease (PID) 
  • Helicobacter pylori infection as part of a combination therapy 

How do you use Metronidazole? 

Availability: Metronidazole is available in several forms, including tablets, extended-release tablets, capsules, topical creams, gels, lotions, and an injectable form.

Dosage information: 

  • Adults: The dose varies based on the type of infection treated, commonly ranging from 250 mg to 750 mg three times a day. 
  • Children: Dosage is often based on weight, and the doctor will determine the appropriate dose. 


  • Children: Yes, with a doctor's prescription and appropriate dosage. 
  • Adults: Yes, with a doctor's prescription. 
  • Elderlies: Yes, though they may require dosage adjustments due to potential decreased liver and kidney function. 
  • Pregnancy: Generally safe for use (FDA Category B) with proper medical guidance; advise topical preparation use if possible 
  • Lactation: Metronidazole can be excreted in milk, use should be guided by professional medical advice 

Who can’t take Metronidazole? 

  • Individuals with a known allergy to metronidazole or other nitroimidazoles should not take this medication. 
  • It is contraindicated in patients with a history of blood disorders 
  • May cause severe side-effects in alcoholics (disulfiram-like reactions), use alternatives as much as possible 

Any warnings and precautions: 
Metronidazole should be taken with caution in patients with liver disease. Alcohol should be avoided during treatment and for at least 48 hours after the last dose due to the risk of a disulfiram-like reaction i.e. nausea, vomiting, dizziness, headache, palpitations, confusion, agitation, abdominal pain, convulsions, coma. 

Drug and Food/Beverage Interactions  
Metronidazole can interact with warfarin, lithium, phenytoin and ciclosporin among other drugs. Concomitant use with alcohol and propylene glycol containing food, beverage and medicinal preparations can produce adverse effects.

Side Effects

Common side effects include nausea, diarrhea, and a metallic taste in the mouth. Severe side effects may include allergic reactions, seizures, and liver problems. 

Pharmacist Tips

  • Storage information: 
    Keep Metronidazole at room temperature away from moisture and heat. Ensure it's out of reach of children. 
  • Handling instructions: 
    Wash hands before and after using Metronidazole, especially if using topical forms. Swallow tablets whole with water, preferably with food. 
  • Monitoring for side effects: 
    Watch for common side effects like nausea or headaches. Report severe reactions to a healthcare provider immediately. 
  • Avoiding alcohol: 
    Do not drink alcohol during and for 48 hours after the Metronidazole course to prevent adverse reactions. 
  • Regular check-ups: 
    Continue taking Metronidazole for the full prescribed length of time, even if symptoms improve, and have regular follow-ups with your doctor. 
  • Disposing of expired medication: 
    Properly dispose of expired or unused Metronidazole by returning it to a pharmacy or a take-back program. 
  • Consultation with healthcare professionals: 
    For any concerns, consult your pharmacist or doctor for personalized advice on Metronidazole use. 


Where is Metronidazole available in Hong Kong?

Metronidazole is a prescription medication that can be prescribed by healthcare providers.


Is Metronidazole for purchase over-the-counter?

No, Metronidazole requires a prescription from a healthcare professional.

Can I drink alcohol while taking Metronidazole?

You should not drink alcohol while taking Metronidazole and for at least 48 hours after completing your course of the drug.

How long does it take for Metronidazole to work?

The time it takes for Metronidazole to work can vary depending on the type of infection, but some symptoms may improve within 24 to 48 hours. Always complete the full course of treatment. 

This website provides content related to drug use and medicine for informational purposes only. It is not a substitute for professional medical advice, diagnosis, or treatment. Do not use the information on this website to diagnose or treat a health problem or disease without consulting a qualified healthcare provider. The website's owners and contributors are not liable for any repercussions, adverse effects, or consequences resulting from the use of any medication or information provided herein.

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