Metronidazole is a prodrug, meaning it is inactive until it is chemically reduced inside the cell.
Anaerobic bacteria and protozoa (e.g. Bacteroides, Clostridioides, Entamoeba) live in low-oxygen environments. These organisms possess low redox potential electron-transport proteins like ferredoxin. These proteins reduce the nitro group of metronidazole, this reduction converts metronidazole into toxic free radical metabolites. The free radicals damage DNA causing strand breaks and cell death.
In presence of oxygen it stops from working as oxygen competes for electrons. the reduced metronidazole is rapidly re-oxidized back to its inactive form and free radicals cannot accumulate. therefore, aerobic bacteria cannot activate metronidazole.
“Metronidazole is selectively toxic to anaerobes because only low-oxygen environments allow reduction of its nitro group into DNA-damaging free radicals”
Metronidazole WORKS best;
- Anaerobic infections
- Intra-abdominal abscess
- Pelvic infection
- Dental infection
- Brain abscess
- GI Infections
- Clostridioides difficile colitis
- Amoebiasis (Entamoeba histolytica)
- Giardiasis
- Low-oxygen tissues
- Necrotic tissue
- Pus-filled abscesses
Metronidazole WON’T WORK;
- Aerobic bacteria (e.g. E.coli, Staphylococcus)
- Well-oxygenated tissues without anaerobes
If oxygen can inactivate an antibiotic like metronidazole, how important do you think understanding the infection site is before choosing the right medicine?
MBH/AB
