Source: Medicines and Medical Devices Safety Authority (NZ) Revision Year: 2022 Publisher: Pharmacy Retailing (NZ) Ltd t/a Healthcare Logistics, PO Box 62027, Sylvia Park Auckland 1644, Freecall: 0800 283 684, Email: medinfo.australia@sanofi.com
Pharmacotherapeutic group: Antibacterials for systemic use
ATC code: J01XD01
Antiprotozoal agent; anaerobic antibacterial agent.
Flagyl is active against a wide range of pathogenic micro-organisms notably species of Bacteroides, Fusobacteria, Clostridia, Eubacteria, anaerobic cocci and Gardnerella vaginalis. It is also active against Trichomonas, Entamoeba histolytica, Giardia lamblia and Balantidium coli.
It is suggested that unchanged metronidazole penetrates the protozoan cell, where the nitro group is reduced to a hydroxyl or amine group which reacts with DNA and stops nucleic acid synthesis.
The bioavailability of metronidazole in Flagyl suppositories is 60-80%. Effective blood concentrations are achieved 5-12 hours after the first suppository and are maintained by the recommended 8-hourly regimen.
Metronidazole is widely distributed into most body tissues and fluids where it achieves concentrations similar to those in plasma. Metronidazole is not protein bound to any significant degree. Metronidazole is metabolised by oxidation in the liver to a number of metabolites, one of which (the hydroxy metabolite) has some antibacterial activity.
The elimination half-life of metronidazole is 7-8 hours, and that of the hydroxyl metabolite slightly longer. About 55 to 80 percent of an administered dose is excreted in the urine as nitrocontaining compounds, of which unchanged metronidazole and the hydroxymethyl homologue each comprise about one third. The fate of the remainder is unknown.
Metronidazole should be administered with caution to patients with advanced hepatic insufficiency. Metronidazole can be used in chronic renal failure; it is rapidly removed from the plasma by dialysis. Metronidazole is excreted in breast milk but the intake of a suckling infant of a mother receiving normal dosage would be considerably less than the therapeutic dosage for infants.
Metronidazole has been shown to be carcinogenic in the mouse and in the rat. However, similar studies in the hamster have given negative results and extensive human epidemiological studies have provided no evidence of increased carcinogenic risk in humans.
Metronidazole has been shown to be mutagenic in bacteria, in vitro. In studies conducted in mammalian cells, in vitro, as well as in rodent or humans in vivo, there was inadequate evidence of a mutagenic effect of metronidazole.
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