Metronidazole

Emma Farrell

Mechanism of Action:

Antibiotic and antiprotozoal agent. Metronidazole is a 5-nitroimidazole derivative that has activity against protozoa and anaerobic bacteria. It is reduced by microbial nitroreductase to an unstable intermediate that interacts with DNA, inhibits with nucleic acid synthesis and prevents further replication. It is used for the treatment of infections involving anaerobic bacteria as well as protozoal infections.

Lecture and CAL materials:

Drug specifics

Alternative drug name not specified
Effects Metronidazole has many indications. (i) Antiparasitic - active against certain protozoa (Entamoeba histolytica, Giardia lamblia, Trichomonas vaginalis). (ii) Anaerobic bacteria such as Bacteroides spp, Clostridium spp, and Helicobacter pylori. (iii) Prevention of infection during surgery on the GI system that is likely to release anaerobic species. (iv) Treatment of antibiotic-associated colitis (pseudomembranous colitis). (v) Leg ulcers and pressure sores. (vi) Bacterial vaginosis. (vii) Pelvic inflammatory disease (viii) Acute ulcerative gingivitis and other oral infections. (ix) Helicobacter pylori eradication. (x) Tetanus.
Adverse actions Gastro-intestinal disturbances (including anorexia, nausea and vomiting) are common as are taste disturbance. Many other rarer adverse effects such as peripheral neuropathy, temporary leucopenia, and rashes. Metronidazole has a ‘disulfiram-like reaction’ with alcohol preventing metabolism of the ethanol breakdown product acetaldehyde leading to severe sickness (patients should be warned).
Dose Oral tablets tds but can also be given IV, and by rectum.
Interactions Metronidazole can produce a disulfiram-like reaction when taken in conjunction with alcohol – inhibits metabolism of ethanol, causing nausea and flushing. It inhibits the metabolism of phenytoin and warfarin, and the excretion of lithium. The elimination of metronidazole is itself inhibited by cimetidine.
Contraindications not specified
Comments Eradication of Helicobacter pylori reduces recurrence of gastric and duodenal ulcers. The presence of H. pylori should be confirmed before starting eradication treatment. Acid inhibition combined with antibacterial treatment is highly effective in the eradication of H. pylori; reinfection is rare. For initial treatment, a one-week triple-therapy regimen that comprises a proton pump inhibitor, clarithromycin, and either amoxicillin or metronidazole should be used. These regimens eradicate H. pylori in about 85% of cases. Treatment failure usually indicates antibacterial resistance or poor compliance. Resistance to amoxicillin is rare but resistance to clarithromycin and metronidazole is common and can develop during treatment. Two-week triple-therapy regimens offer the possibility of higher eradication rates compared to one-week regimens, but adverse effects are common and poor compliance is likely to offset any possible gain.
Contributors