Source: Health Products Regulatory Authority (ZA) Revision Year: 2022 Publisher: Fresenius Kabi Manufacturing SA (Pty) Ltd, 6 Gibaud Road, Korsten, Port Elizabeth 6020, South Africa
Category and class: A 20.2 Antimicrobial agents.
Pharmacotherapeutic group: Antibacterials for systemic use: imidazole derivatives
ATC code: J01XD01
Metronidazole is active against a variety of anaerobic bacteria, particularly Bacteroides fragilis. Metronidazole has antiprotozoal activity against Trichomonas vaginalis and other protozoa, including Entamoeba histolytica and Giardia lamblia. It does not affect the acidophilic flora of the vagina and it has no effect on em>Candida/em> species. Its mechanism of action is reflected in a selective toxicity to anaerobic or microaerophilic micro-organisms and for other anoxic or hypoxic cells. In susceptible cells the nitro group of metronidazole is reduced by electron transport proteins with low redox potentials (such as ferredoxin in Clostridia); these proteins play a much more important role in the metabolism of such cells than they do in aerobes. Metronidazole thus acts as an electron sink and deprives the cell of required reducing equivalents.
The following has been proposed as the mode of action of metronidazole: the parent compound penetrates the cell membrane unchanged, but once inside the cell the nitro group is reduced in the redox condition prevalent in the anaerobic cell. The reduced product is known to damage deoxyribonucleic acid (DNA) causing eventual death of the organism.
The elimination half-life of metronidazole is about 8 hours; that of the hydroxyl metabolite is slightly longer. The half-life of metronidazole is reported to be longer in neonates and in patients with severe hepatic impairment; that of the hydroxyl metabolite is prolonged in patients with substantial renal impairment (see section 4.4). Metronidazole is absorbed from the gastrointestinal tract and widely distributed in body tissue. Approximately 30–40% of a dose is metabolised in the liver; the majority of a dose of metronidazole is extracted in the urine, mainly as metabolites; a small amount appears in the faeces.
Metronidazole is able to pass the blood-brain barrier. It reaches therapeutic concentrations in most other body fluids, i.e. saliva, bile, urine, amniotic fluid, breastmilk and in abscess cavities.
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