Metronidazole belongs to the class of nitroimidazoles. It inhibits nucleic acid synthesis by forming nitroso radicals that disrupt the DNA of microbial cells. This function occurs only when metronidazole is partially reduced, and since this reduction normally occurs only in anaerobic bacteria and protozoa, it has relatively little effect on human cells or aerobic bacteria.
Orally ingested metronidazole is approximately 80% bioavailable through the intestine and maximum blood plasma concentrations occur after one to two hours. Food may slow absorption but does not decrease it. Of the given dose, about 20% is bound to plasma proteins. It penetrates well into tissues, cerebrospinal fluid, amniotic fluid, and breast milk, and into abscess cavities. Approximately 60% of metronidazole is metabolized by oxidation to the major metabolite hydroxymetronidazole and a carboxylic acid derivative, and by glucuronidation. Metronidazole and its metabolites are excreted mainly by the kidneys (77%) and to a lesser extent by the faeces (14%). The biological half-life in healthy adults is approximately eight hours.
Concomitant consumption of alcohol may cause nausea, vomiting, flushing of the skin, tachycardia and shortness of breath. For this reason, consumption of alcoholic beverages is not recommended.
Metronidazole inhibits the enzyme CYP2C9, so it may interact with drugs metabolized by these enzymes (eg, lomitapide, warfarin).