Metronidazole (Flagyl)

Generic Name: Metronidazole

Brand Names:
Oral: Flagyl
Topical: Rozex, MetroCream, Metrogel, Metrolotion

What is Metronidazole used for?
Metronidazole (Flagyl) is an imidazole prescription antibiotic. Its antimicrobial spectrum includes many pathogenic gram-positive and gram-negative anaerobes and protozoal parasites.

Metronidazole is used in the treatment of amebiasis, trichomoniasis, anaerobic infections (bacterial vaginosis, dental infections, peritonitis, intra-abdominal abscess); prophylaxis of postoperative infections.

Topical Metrogel is indicated for the treatment of rosacea.


  • Hypersensitivity to nitroimidazole derivatives or any component of the products.
  • First trimester of pregnancy in patients with trichomoniasis.

Metronidazole dosage:

Tablets may be taken with or without food. However, extended-release form Flagyl ER should be taken on an empty stomach, at least 1 hour before or 2 hours after eating a meal.


Trichomoniasis ("trich") is a sexually transmitted disease (STD) caused by Trichomonas vaginalis. Trichomonas vaginalis was discovered in 1836 and has been known to cause vaginitis since 1916. However, there was no effective cure until the discovery of metronidazole in 1957 by French scientists.

Originally metronidazole was developed for use as an antitrichomonal medicine. Metronidazole provides a cure rate of 90-95% in the treatment of trichomoniasis.


  • One-day dosage regimen: 2 g taken as a single dose. This one-day trichomoniasis treatment provides 90-95% cure rate.
  • Seven-day dosag regimen: 400-500 mg twice daily for 7 days.

To prevent reinfection simultaneous treatment of sexual partner is obligatory!


  • 15 mg/kg daily in 3 divided doses for 7 days.

Intravaginal therapy for trichomoniasis is ineffective, because the parasite can be present in inaccessible areas.

Anaerobic Bacterial Infections

Adults: Usual dosage is 500 mg every 8 hours (on the basis of 7.5 mg/kg every 6 to 8 hours, maximum 4 g per day) for 7 to 10 days.

Children: 7.5 mg/kg every 8 hours.

Serious anaerobic infections may require I.V. administration.

Amoebiasis (amoebic dysentery, amoebic liver abscess)

Amoebiasis is caused by Entamoeba histolytica. Amebic dysentery is the usual consequence of the infection. Amebic liver abscess is a result of haematogenic spread of parasite along the portal vein.

Adults: 500-750 mg every 8 hours for 5 to 10 days.

Children: 35 to 50 mg/kg daily in divided doses every 8 hours for 10 days.


Topical metronidazole has been widely prescribed for rosacea and is considered a first-line therapy. It can significantly improve redness, inflammatory papules and pustules of rosacea. However, metronidazole has no favourable effect on telangiectasia.

Metronidazole cream, gel, and lotion at concentrations of 0.75% and 1%, in dosing regimens of once or twice daily, all bring on similar perfect results.

Metronidazole side effects:

  • CNS: headache, dizziness, seizures, peripheral neuropathy, vertigo, incoordination, ataxia, confusion, irritability, weakness.
  • Dermatologic: urticaria, erythematous rash, flushing.
  • EENT: metallic taste, glossitis.
  • GI: nausea, vomiting, diarrhea, constipation, abdominal discomfort/cramps, epigastric distress.
  • Genitourinary: vaginitis, vaginal Candida proliferation, darkening of urine, vaginal irritation and dryness, urethral burning, dysuria, pelvic discomfort, polyuria, dyspareunia.


Take the entire prescribed course of antibiotic. Your symptoms may get better before the infection is completely cured. Follow the instructions on your prescription label.

Inform your doctor if you have any allergies. Tell your doctor if you are taking any other medicines, including those you buy without prescription from a pharmacy or health food store.

  • Children: Safety and efficacy not established, except for amebiasis.
  • Elderly: Monitoring serum levels may be necessary for proper dosing.
  • Liver function: Patients with severe hepatic disease should use it with caution due to potential accumulation.
  • Candidiasis: Known or previously unrecognized candidiasis may present more prominent symptoms during therapy.
  • Blood dyscrasias: Use with caution in patients with a history of blood dyscrasias.
  • Neurologic effects: Seizures and peripheral neuropathy have ccurred. Use extra caution with prolonged use, high doses, or history of CNS disease.


  • Alcohol: Metronidazole taken in combination with alcohol may produce disulfiram-like reaction - unpleasant effects such as abdominal cramps, nausea, vomiting, and flushing. Metronidazole is guessed to block the breakdown of alcohol, leading to accumulation of acetaldehyde in the blood.
    Try to avoid alcohol during treatment and for at least 3 days after.
  • Disulfiram: In a clinical trial of combined therapy with disulfiram and metronidazole in the treatment of chronic alcoholics, severe acute psychotic reactions occurred in 6 out of 29 patients.
  • Warfarin: Metronidazole inhibits the breakdown of the more potent S-isomer of warfarin. This is the pharmacologically active metabolite of the racemic parent molecule. Therefore, the activity of warfarin is enhanced by metronidazole.

Interference with Clinical Laboratory Tests:

  • Metronidazole may show negative interference with continuous flow spectrophotometry of aspartate aminotransferase (previously GOT) so that hepato-cellular damage which is detectable by raised serum AST may be missed.

Pregnancy & Lactation:
Pregnancy Risk Factor: B (no proven risk)
Although metronidazole is in the FDA category B (meaning it is unlikely to be harmful to the fetus), it should be avoided during the 1st trimester of pregnancy because of concerns about its mutagenicity.

Because of the potential for tumorigenicity, shown in mouse and rat studies, a decision should be made whether to discontinue nursing or to discontinue metronidazole, taking into account the importance of the treatment to the mother. Metronidazole is secreted in human milk in concentrations similar to those found in plasma.


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