Metronidazole is an antibiotic that belongs to the nitroimidazole class. It is available in tablet form, most commonly as 200 mg and 400 mg pills. In Hong Kong, Metronidazole is a prescription-only medication regulated by the Department of Health under the Pharmacy and Poisons Ordinance. The drug is also approved by major agencies such as the U.S. Food and Drug Administration (FDA) and the European Medicines Agency (EMA).
Metronidazole’s primary clinical use is to treat infections caused by anaerobic bacteria and certain protozoa. The tablets can be taken orally with or without food, and dosage is individualized by a prescriber based on the type and severity of the infection.
Metronidazole is a pro-drug that becomes active after entering microbial cells. Inside anaerobic organisms, it is reduced by ferredoxin proteins to generate reactive nitro-radical metabolites. These metabolites bind to DNA and other critical macromolecules, causing strand breaks and loss of protein function. The result is irreversible damage to the pathogen’s DNA, leading to cell death.
Because the reduction process occurs primarily in low-oxygen environments, Metronidazole selectively targets anaerobic bacteria and protozoa while sparing most human cells. The drug is well absorbed from the gastrointestinal tract, reaches peak plasma concentrations within 1-2 hours, and has a half-life of about 8 hours in healthy adults. It is metabolized in the liver and excreted mainly in urine.
Metronidazole is approved for a range of bacterial and protozoal infections, including:
In Hong Kong, these indications align with the product labeling approved by the Department of Health. The drug is also frequently used in dental infections, postoperative prophylaxis, and certain cases of Clostridioides difficile-associated diarrhea, although the latter use follows clinical judgment rather than a formal indication.
Metronidazole has been studied for several off-label applications. Where peer-reviewed evidence exists, the use remains not approved by regulatory agencies and should be undertaken only under medical supervision.
Off-label use requires medical supervision and individualized risk assessment.
If you have any of these conditions, discuss alternatives with your healthcare provider.
These effects are usually mild and resolve after completing therapy.
When in doubt, inform your pharmacist or prescriber of all medicines, supplements, and herbal products you are using.
Always follow the specific instructions provided by your prescriber.
If new symptoms such as tingling, severe abdominal pain, or skin rash appear, contact a healthcare professional promptly.
This article provides educational information about Metronidazole and is not a substitute for professional medical advice. Treatment decisions, including use for unapproved indications, must be made under the guidance of a qualified healthcare provider. The content is intended for informational purposes and does not constitute medical recommendations. Always consult a physician before starting, stopping, or changing any medication regimen.
No. Alcohol consumption may cause a disulfiram-like reaction, which includes flushing, nausea, vomiting, and rapid heart rate. Avoid alcohol throughout the treatment period and for at least 48 hours after the final dose.
Therapeutic effects often begin within 1-2 days, but full clinical improvement may take several days depending on the infection type and severity.
Take the missed tablet as soon as you remember unless it is close to the time for your next scheduled dose. Do not take a double dose to make up for the missed one.
The medication can be taken with or without food. If you experience stomach upset, taking it with a meal may help.
The drug and its metabolites can interact with taste receptors, producing a transient metallic sensation that usually resolves after the course is completed.
Mild to moderate liver impairment may not require dose adjustment, but severe hepatic disease often warrants a lower starting dose and careful monitoring.
It is generally avoided in the first trimester. Use in later trimesters is considered only when the potential benefits outweigh the risks, and always under medical supervision.
Symptoms may include rash, itching, swelling (especially of the face, tongue, or throat), severe dizziness, or difficulty breathing. Seek emergency care immediately if these occur.
Keep them at room temperature away from moisture, heat, and direct sunlight. Store them out of reach of children and discard any tablets that are past their expiration date.
