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Metronidazole Some Trade Names
FLAGYL
Click for Drug Monograph
is bactericidal. It enters bacterial cell walls and interrupts DNA.

Pharmacology

Oral metronidazole Some Trade Names
FLAGYL
Click for Drug Monograph
is absorbed well. It is usually given IV only if patients cannot be treated orally. It is distributed widely in body fluids and penetrates into CSF, resulting in high concentrations. Metronidazole Some Trade Names
FLAGYL
Click for Drug Monograph
is metabolized presumably in the liver and excreted mainly in urine, but elimination is not decreased in patients with renal insufficiency.

Indications

Metronidazole Some Trade Names
FLAGYL
Click for Drug Monograph
is active against

• All obligate anaerobic bacteria (it is inactive against facultative anaerobic and aerobic bacteria)
• Certain protozoan parasites (eg, Trichomonas vaginalis, Entamoeba histolytica, Giardia lamblia)

Metronidazole Some Trade Names
FLAGYL
Click for Drug Monograph
is used primarily for infections caused by obligate anaerobes, often with other antimicrobials. Metronidazole Some Trade Names
FLAGYL
Click for Drug Monograph
is the drug of choice for bacterial vaginosis. The drug has other clinical uses (see Table 14: Bacteria and Antibacterial Drugs: Some Clinical Uses of Metronidazole).

Table 14
Some Clinical Uses of Metronidazole Indication Comments Infections due to obligate anaerobes (eg, intra-abdominal, pelvic, soft-tissue, periodontal, and odontogenic infections; lung abscess) Often used with other antimicrobials Bacterial vaginosis Drug of choice Crohn's disease — CNS infections (meningitis, brain abscess) — Endocarditis — Septicemia — Prophylaxis before intestinal surgery — Clostridium difficile–induced diarrhea (pseudomembranous colitis) Oral use preferable Peptic ulcers due to Helicobacter pylori For treatment and prevention of relapses Used with other drugs Acne rosacea Topical or oral use

Contraindications

Metronidazole Some Trade Names
FLAGYL
Click for Drug Monograph
is contraindicated in patients who have had an allergic reaction to it.

Use During Pregnancy and Breastfeeding

Metronidazole Some Trade Names
FLAGYL
Click for Drug Monograph
is in pregnancy category B (animal studies show no risk and human evidence is incomplete, or animal studies show risk but human studies do not). Nonetheless, metronidazole Some Trade Names
FLAGYL
Click for Drug Monograph
should be avoided during the 1st trimester because mutagenicity is a concern.

Metronidazole Some Trade Names
FLAGYL
Click for Drug Monograph
enters breast milk; use during breastfeeding is not recommended.

Adverse Effects

Adverse effects include

• GI disturbances
• CNS effects and peripheral neuropathy
• Disulfiram Some Trade Names
  ANTABUSE
  Click for Drug Monograph
  -like reaction

Nausea, vomiting, headache, seizures, syncope, other CNS effects, and peripheral neuropathy can occur; rash, fever, and reversible neutropenia have been reported. Metronidazole Some Trade Names
FLAGYL
Click for Drug Monograph
can cause a metallic taste and dark urine. A disulfiram Some Trade Names
ANTABUSE
Click for Drug Monograph
-like reaction may occur if alcohol is ingested within 7 days of use.

Dosing Considerations

Metronidazole Some Trade Names
FLAGYL
Click for Drug Monograph
doses are not decreased in patients with renal failure but are usually decreased 50% in patients with significant liver disease.

Metronidazole Some Trade Names
FLAGYL
Click for Drug Monograph
inhibits metabolism of warfarin Some Trade Names
COUMADIN
Click for Drug Monograph
and may increase its anticoagulant effect.

Last full review/revision July 2009 by Matthew E. Levison, MD

Content last modified July 2009