Metronidazole (Flagyl / Flagyl S / Metrolyl)

Metronidazole (Flagyl / Flagyl S / Metrolyl) is an anti-microbial drug that is highly active against a wide range of bacteria and protozoa. It is used to treat infections with Entamoeba histolytica, Giardia lamblia and bacterial infections of the vagina. It is being studied as a treatment for microsporidiosis and as maintenance therapy to prevent recurrences of isosporiasis.

The most common side-effects are headache, nausea, dry mouth and a metallic taste. It can also cause dark urine, fatigue, depression, headaches, vomiting and fever. Rare serious toxicities can include peripheral neuropathy and seizures.

Metronidazole also causes alcohol intolerance. Patients taking metronidazole should avoid alcoholic drinks. Metronidazole should also be avoided by patients taking formulations of protease inhibitors that contain ethanol or propylene gycol. These include amprenavir (Agenerase) solution, ritonavir-boosted lopinavir (Kaletra) solution, ritonavir (Norvir) capsules and tipranavir (Aptivus) capsules.

Because it kills off some of the natural bacteria found in the healthy mouth or vagina, a course of metronidazole can result in thrush of the mouth or vagina. It may also decrease the effectiveness of oral contraceptives.

Metronidazole is available as generic (non-brand name) tablets or a liquid for intravenous infusion. It is also manufactured in these forms and as suppositories by several pharmaceutical companies under the tradenames Flagyl (Rhone-Poulenc Rorer), Metrogel, Metrotop and Metrolyl (Lagap) and Zadstat (Lederle).

Tinidazole is a closely related drug that has similar effects, but has a longer duration of action. It is produced by Pfizer under the tradename Fasigyn.