Metronidazole / Flagyl





  • Tablets: 250 mg, 500 mg
  • Capsules: 375 mg
  • Injectable: 5 mg/mL




  • Tablets: 200 mg, 400 mg
  • Suspension: 200 mg/5mL in 30 mL or 60 mL bottles


Metronidazole is both a powerful bactericidal agent with activity against most anaerobic bacteria (bacteria that does not require the presence of oxygen to grow), and an amebicide with effective activity against Entamoeba histolytica, Trichomonas, Giardia and Balantidium coli.

The drug is rapidly absorbed and widely distributed from the gastrointestinal tract. It is found in most body tissues, including bone, abscesses, CNS, as well as crossing the placental barrier. Metronidazole is metabolized in the liver and excreted in milk, feces, and urine, coloring the urine dark brown.

It is recommended to avoid use in pregnant and lactating animals, unless benefit outweighs risk.


Used in bone infections, infections of the tooth socket and abscesses where anaerobic bacteria are likely to be present, and in other enteric and systemic anaerobic infections.

Drug Interactions or Contraindications

  • Contraindicated in rats where neurological disorders are present.
  • Not recommended for nursing or pregnant animals.
  • Avoid concurrent use with phenobarbital, and cimetidine.
  • It is compatible with all but the following drugs:
    • aztreonam
    • cefamandole nafate (second generation cephalosporin antibiotic)
    • dopamine hcl

    Adverse Reactions

    CNS: lethargy, weakness, poor coordination

    Blood: transient neutopenia, leukopenia

    Endocrine: hypoglycemia, hypocalcemia

    GI: anorexia, diarrhea, stomatitis

    GU: darkened or red-brown urine, cystitis, polyuria, dysuria

    Skin: pruritus (itching)

    Other: hepatotoxicity

    Dosage Recommendations

    10 mg to 40 mg/animal (rat), PO, q24hr  2, 26, 34, 35


    10 mg/kg to 40 mg/kg, PO. Give twice 5 days apart when treating for protozoa.  35


    10 mg/kg to 50 mg/kg, q12hr   11


    20 mg/kg to 40 mg/kg, PO, q24hr (rats) 41, 42 44


    50 mg/kg to 60 mg/kg, PO, q12hr for 5 days 41, 44


    • Give with food to avoid GI distress.
    • In treating suspected polymicrobial infections, where a broader coverage may be needed, synergistic or combination drugs may be used. The following drugs may be seen used simultaneously with metronidazole: aminoglycosides (e.g., amikacin or gentamicin), fluoroquinolones (e.g., enrofloxacin or orbifloxicin), chloramphenicol. 141
    • Tablets and powder for injection should be stored at less than 30 degrees and protected from light.


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