Metronidazole is a nitro-imidazole drug which has antiprotozoal and anti-anaerobe activity.


Protozoans – Entamoeba histolytic, Giardia lamblia, Trichomonas vaginalis

Bacteria – Camphylobacter jejuni, Helicobacter pylori, Fusobacterium, Bacteriodes fragilis, Spirochaetes, Clostridium perfringens, Clostridium difficile

Mechanism of action

Metronidazole has a nitro group which is converted into nitro radicle by the redox proteins of anaerobes. This acts as an electron acceptor and the availability of electrons to the electron transport chain is reduced. Certain organizms develop resistance to metronidazole by preventing the generation of nitro radicle.


Metronidazole is completely absorbed from the intestine and very little reaches the colon.

Adverse effects

CNS side effects, peripheral neuropathy, anorexia, nausea, metallic taste in mouth, head ache, neutropenia, rashes, thrombophlebitis when injected.

Contra indications

Chronic alcoholism because of disulfiram like reaction (Antabuse like reaction), neurological disorders, blood dyscrasias.

Drug interactions

Rifampicin and barbiturates induce hepatic metabolism. Cimetidine reduces the metabolism. Both these are by the action on CYP450.

Uses of metronidazole

Amoebiasis – 800 mg thrice daily for 7 to 10 days is given for amoebic liver abscess. In severe infections, intravenous therapy is initially given and followed by oral therapy. 400 mg thrice daily for mild intestinal amoebiasis.

It is also indicated in Giardiasis and Trichomoniasis.

Metronidazole is used in the triple drug regimen for Helicobacter pylori infection in peptic ulcer.

It can also be given in pseudomembranous colitis due to Clostridium difficile.

Metronidazole can be given for anaerobic infection after pelvic or colorectal surgery. Gentamicin is added as it is usually a mixed infection.

Trench mouth (ulcerative gingivitis) caused by fusobacterium is also treated with metronidazole.

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