MetronidazoleSome Trade Names
FLAGYL
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is bactericidal. It enters bacterial cell walls and interrupts DNA.

Pharmacology

Oral metronidazoleSome Trade Names
FLAGYL
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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. MetronidazoleSome Trade Names
FLAGYL
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is metabolized presumably in the liver and excreted mainly in urine, but elimination is not decreased in patients with renal insufficiency.

Indications

MetronidazoleSome Trade Names
FLAGYL
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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 intestinalis [lamblia])

MetronidazoleSome Trade Names
FLAGYL
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is used primarily for infections caused by obligate anaerobes, often with other antimicrobials. MetronidazoleSome Trade Names
FLAGYL
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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
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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

MetronidazoleSome Trade Names
FLAGYL
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is contraindicated in patients who have had an allergic reaction to it.

Use During Pregnancy and Breastfeeding

MetronidazoleSome Trade Names
FLAGYL
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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, metronidazoleSome Trade Names
FLAGYL
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should be avoided during the 1st trimester because mutagenicity is a concern.

MetronidazoleSome Trade Names
FLAGYL
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enters breast milk; use during breastfeeding is not recommended.

Adverse Effects

Adverse effects include

• GI disturbances
• CNS effects and peripheral neuropathy
• DisulfiramSome 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. MetronidazoleSome Trade Names
FLAGYL
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can cause a metallic taste and dark urine. A disulfiramSome Trade Names
ANTABUSE
Click for Drug Monograph
-like reaction may occur if alcohol is ingested within 7 days of use.

Dosing Considerations

MetronidazoleSome Trade Names
FLAGYL
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doses are not decreased in patients with renal failure but are usually decreased 50% in patients with significant liver disease.

MetronidazoleSome Trade Names
FLAGYL
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inhibits metabolism of warfarinSome Trade Names
COUMADIN
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and may increase its anticoagulant effect.

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

Content last modified February 2012