Pharmacology · Class
Nitroimidazoles !
Prodrugs activated only inside anaerobes and protozoa, where they shred DNA. For anaerobes, trichomoniasis, giardiasis and amoebiasis.
Updated 2026-11-01
What they are
Metronidazole, tinidazole and secnidazole. They act on anaerobic bacteria and on protozoa such as Trichomonas, Giardia and Entamoeba, which have the low-redox electron carriers needed to switch them on.
Mechanism of action
The drug enters by diffusion. In anaerobic cells, proteins such as ferredoxin pass an electron to its nitro group and form short-lived reactive radicals. These damage DNA, break its strands and kill the cell. Aerobic human cells barely reduce the drug, which explains the selectivity.
Target: DNA, after reductive activation of the nitro group inside the microbe
Drugs in this class
- MetronidazoleThe reference drug for anaerobes and for trichomoniasis, giardiasis and amoebiasis. Alcohol is avoided during and…DNA of anaerobic bacteria and protozoa (after reduction of the nitro group)
- TinidazoleA longer-acting relative of metronidazole, often given as a single dose for trichomoniasis and giardiasis. Alcohol is…DNA of anaerobic bacteria and protozoa (after reduction of the nitro group)
- SecnidazoleA long-acting nitroimidazole given once, as granules on soft food, for bacterial vaginosis and trichomoniasis.DNA of anaerobic bacteria and protozoa (after reduction of the nitro group)
Others in the class
- ornidazole
- benznidazole (Chagas disease)
- fexinidazole (sleeping sickness)
Test yourself
Think of the answer, then tap the question to see it.
Why do nitroimidazoles act only on anaerobes and protozoa?
Only their low-redox electron carriers can reduce the nitro group to the reactive radicals that damage DNA.
What happens if a patient drinks alcohol while taking metronidazole?
A disulfiram-like reaction: flushing, nausea, vomiting, cramps and headache.
Which nitroimidazole effects are expected and harmless?
A metallic taste and darker urine.
Educational content on how drugs work; not a prescribing guide and no substitute for a health professional's advice. No doses are given.
Sources: DailyMed - METRONIDAZOLE tablet (DailyMed (U.S. National Library of Medicine), 2026); DailyMed - TINIDAZOLE tablet (DailyMed (U.S. National Library of Medicine), 2026); Secnidazole: MedlinePlus Drug Information (MedlinePlus (U.S. National Library of Medicine), 2026); eEML - Electronic Essential Medicines List (World Health Organization, 2025).
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Representative model, for educational purposes only.