Practical information on using nitroimidazoles
The nitroimidazoles metronidazole and tinidazole1 have activity against almost all gram-negative anaerobic bacteria (eg Bacteroides fragilis) and most gram-positive anaerobic bacteria (eg Clostridium species, but not Cutibacterium acnes [formerly Propionibacterium acnes]). They are also active against protozoa, including Trichomonas vaginalis, Giardia intestinalis and Entamoeba histolytica. Helicobacter pylori resistance to metronidazole is common in Australia (about 30 to 50% of H. pylori infections, reflecting high community exposure to nitroimidazole drugs).
Metronidazole may cause nausea, vomiting, flushing, headache and palpitations if taken concomitantly with alcohol; it is similar to the reaction that occurs when alcohol is taken with disulfiram. Although clinical data on the frequency of this reaction are conflicting, avoidance of alcohol during treatment and for at least 24 hours after completing the course of metronidazole is suggestedFjeld, 2014Mergenhagen, 2020.
For the treatment of mixed aerobic and anaerobic infections in these guidelines, the recommended dosage of metronidazole is 400 mg orally or 500 mg intravenously, 12-hourly. The 12-hourly dosing regimen is based on pharmacokinetic data and minimum inhibitory concentrations of the pathogens involved, in addition to limited clinical studies and extensive clinical experience with its use.