Metronidazole

Metronidazole is a commonly used antibiotic that belongs to the nitroimidazole class of antibiotics. It is commonly used to treat gastrointestinal infections as well as trichomoniasis and giardiasis and amoebiasis, which are caused by parasites. Metronidazole has also been used for several decades as an antibiotic against many bacterial infections.

It is available in capsule, tablet, topical, and suppository form for the treatment of various infections.

Pharmacodynamics

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.

Pharmacokinetics

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.

Drug Interactions

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).

Side effects

Common side effects are nausea, a metallic taste, loss of appetite, and headache.

Occasionally, seizures or allergies to the drug may occur. Experts disagree about the use of metronidazole during pregnancy or breastfeeding.

Metronidazole is suspected of causing cancer in humans. This suspicion has not yet been confirmed. Metronidazole is therefore listed as a possible carcinogen by the World Health Organization (WHO).

Toxicological data

LD50 (rat, oral): 3000 mg-kg-1