metronidazole
Meaning of metronidazole: The drug arrives inactive and becomes a poison only inside organisms that live without oxygen, which is the source of its narrow aim.
Definition of metronidazole
Metronidazole is an antimicrobial active against anaerobic bacteria, which grow where there is little or no oxygen, and against several single-celled parasites. Those organisms convert the drug into a reactive form that breaks their DNA, a step that oxygen-using cells do not perform. It is used for abdominal, dental, pelvic and skin infections and for parasitic infections.
What does it treat?
| Infection | Organism type |
|---|---|
| Bacterial vaginosis | Overgrowth of anaerobic bacteria |
| Trichomoniasis | Parasite, treated in both partners |
| Giardiasis and amebiasis | Intestinal parasites |
| Abdominal and pelvic infections | Gut anaerobes, usually with another antibiotic covering the rest |
| Dental abscess | Anaerobes of the mouth |
| Clostridioides difficile colitis | Long a common choice, now generally replaced by other agents |
Because its range is narrow, it is often paired with an antibiotic covering organisms that need oxygen, particularly in infections of the abdomen where both kinds are present.
How does it work?
The molecule carries a nitro group and enters cells freely as an inactive compound. Inside an organism that generates energy without oxygen, that group is chemically reduced, producing short-lived reactive fragments that attack DNA and break its strands. The organism cannot repair the damage fast enough and dies. Human cells, and bacteria that use oxygen, do not carry out this reduction, so the drug stays inert in them. That single chemical step explains both the selectivity of the drug and why resistance, when it appears, usually involves a change in how the organism handles the reduction.
What about alcohol?
Product information and long clinical custom describe a disulfiram-like reaction when alcohol is taken during treatment and for a period afterward, with flushing, nausea, vomiting, headache and a fast heartbeat. The reasoning is that the drug interferes with the enzyme clearing acetaldehyde, a breakdown product of alcohol. The evidence behind the warning is thinner than its prominence suggests: it rests largely on case reports, controlled work has not consistently reproduced the reaction, and several reviews have questioned whether the interaction is real. Labels continue to carry the advice, so this remains an unsettled drug interaction rather than an established one. Other recognized effects include a persistent metallic taste, dark urine, nausea, and, with prolonged courses, tingling and numbness from nerve irritation.
Also known as
Used in a sentence
Metronidazole was prescribed for treatment of the diagnosed anaerobic bacterial infection.
Good to know
The disulfiram-like reaction described between metronidazole and alcohol appears on product labels and is taught widely, but the supporting evidence rests largely on case reports and has been questioned in later reviews.