Metronidazole
A nitroimidazole for anaerobic bacteria and protozoa: abdominal and pelvic infections, bacterial vaginosis, trichomoniasis and amebiasis.
Drug card
- Class
- Nitroimidazole
- How it works
- Forming DNA-damaging radicals once reduced inside anaerobic microbes
- Used for
- Serious anaerobic bacterial infections
- Abdominal infections, such as peritonitis and abscess
- Bacterial vaginosis
- Trichomoniasis
- Known for
- Sharp metallic taste
- Disulfiram-like reaction with alcohol
- Its name
- -nidazole means a nitroimidazole antimicrobial
Study it as a flashcard, and it comes back before you forget it.
Mechanism of action
How does metronidazole work?
A prodrug that enters microbes by diffusion. In anaerobic bacteria and protozoa, electron carriers such as ferredoxin reduce its nitro group to a short-lived radical, and the reduced drug damages DNA and kills the cell. It does nothing against aerobic bacteria, so mixed infections need a second antibiotic.
Uses
What is metronidazole used for?
- Serious anaerobic bacterial infections
- Abdominal infections, such as peritonitis and abscess
- Bacterial vaginosis
- Trichomoniasis
- Amebic dysentery and amebic liver abscess
- Giardiasis
Side effects
Side effects of metronidazole
- Sharp metallic tasteKnown for
- Disulfiram-like reaction with alcoholKnown for
- Nausea
- Diarrhea
- Headache
- Peripheral neuropathy, mostly with long coursesSerious
- SeizuresSerious
- Encephalopathy with unsteadiness (ataxia)Serious
- Aseptic meningitisSerious
- Severe skin reactions: SJS, TEN, DRESSSerious
- Long QT interval, mainly with other QT drugsSerious
- Fatal liver failure in Cockayne syndromeSerious
Known for marks what an exam expects you to know it for.
Watch for
Cautions and what sets it apart
- Contraindicated in Cockayne syndrome, where severe liver failure has come on within days.
- Contraindicated in the first trimester when used for trichomoniasis.
- Severe liver impairment: the dose is reduced, as the drug builds up.
- Stop it if numbness, tingling or other new nerve or brain symptoms appear.
Good to know: The standard drug for anaerobes, but blind to aerobic bacteria, so mixed infections such as peritonitis also need an antibiotic that covers aerobes.
Remember it
A way to remember it
GET
- G
- Giardiasis
- E
- Entamoeba histolytica: amebiasis
- T
- Trichomoniasis
GET on the Metro: the three protozoal infections metronidazole and its relatives treat, on top of anaerobic bacteria and bacterial vaginosis.
A mnemonic widely used in teaching
Its name
-nidazole means nitroimidazole antimicrobial
Metronidazole and tinidazole treat anaerobic and protozoal infections. Azole antifungals such as fluconazole and clotrimazole belong to a different group.
- Every drug name stem
Its class
Nitroimidazoles
Nitroimidazoles are prodrugs. They diffuse into microbes, but only in anaerobic bacteria and protozoa do electron carriers such as ferredoxin reduce the drug's nitro group, forming short-lived free radicals. The reduced drug breaks DNA strands and stops DNA synthesis, killing the cell. Aerobic bacteria do not activate them, so the drugs do not treat aerobic infections.
Easily mixed up with nitrofurans and azole antifungals.
Sources
Checked against
Written for biofideX in plain words, after checking these references:
- Metronidazole tablets: label (DailyMed)
- Metronidazole vaginal gel: label (DailyMed)
- Metronidazole (NCI Thesaurus)
- Metronidazole (NHS)
- Patient Care for Giardia Infection (CDC)
For learning pharmacology, not for treatment decisions: no doses are given, and a prescriber, pharmacist or the product's own label is the word on any one patient. Spotted a mistake? Tell us and we'll correct it.
Antibiotics: DNA, folate and tuberculosis
Metronidazole is one of 11 drugs practiced together here: their classes, how they work, what they treat and what they're known for.
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