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Antibiotics - Metronidazole: Nursing Pharmacology



metronidazole (Flagyl)
Produces free radicals inside anaerobic bacteria and protozoans → DNA damage and death
Amebiasis; trichomoniasis; giardiasis; bacterial vaginosis; septicemia; endocarditis; rosacea; bone, joint, lower respiratory tract infections
  • Trichomoniasis, amebiasis, giardiasis: PO
  • Anaerobic bacterial infections: IV
  • Bacterial vaginosis, rosacea: TOP
  • CNS: headache, dizziness, confusion, irritability, insomnia, peripheral neuropathy, seizures, aseptic meningitis (IV)
  • CV: ECG changes
  • EENT: blurred vision, dry mouth, metallic taste
  • GI: anorexia, abdominal cramps, nausea, vomiting, diarrhea, CDI, dry mouth, metallic taste
  • HEMA: bone marrow suppression, leukopenia, thrombocytopenia
  • GU: reddish urine, dysuria
  • INTEG: skin rash, urticaria, phlebitis at injection site, Stevens-Johnson syndrome, toxic epidermal necrolysis
  • Disulfiram-like reaction (combined with alcohol)
  • Boxed warning: carcinogenic
  • Pregnancy, breastfeeding
  • Elderly clients
  • Heart failure
  • Fungal infection
  • CNS, hematologic, gastrointestinal, renal, or hepatic disease
  • Interactions
    • Zalcitabine, disulfiram, cimetidine
    • Warfarin, phenytoin, lithium (impaired CYP2A6 metabolism)
    • Alcohol (increase disulfiram-like reaction)
  • Genitourinary symptoms: unusual vaginal discharge, burning with urination, vaginal pain, irritation or itching, and fish-like odor
  • Laboratory test results: CBC, renal and hepatic function, culture and sensitivity, gram stain, vaginal pH and wet mount results; confirm pregnancy status

  • Side effects
  • Therapeutic effect: resolution of infection
  • Purpose of medication: resolve infection
  • Take full course of medication
    • Orally: twice daily with food
    • Avoid alcohol
    • Intravaginally
      • Self-administration at bedtime, using applicator
      • Do not engage in vaginal intercourse or use products like tampons or douches while being treated with an intravaginal treatment
  • Lifestyle modifications
    • Prevention of recurrence: minimize vaginal irritation, refrain from using douches, limit number of sexual partners, and use condoms
    • Frequent sips of water, good oral hygiene, and hard candies
  • Side effects
    • Dry mouth, bitter or metallic taste
      • Management: frequent sips of water, good oral hygiene, hard sugar-free candies
    • Urine may turn reddish brown
      • Normal side effect of medication
    • Report
      • Symptoms of Clostridioides difficile infection: abdominal pain, severe diarrhea that may become bloody, fever
      • Numbness and tingling of extremities
      • Unusual rash, formation of blisters
      • Easy bruising or bleeding
Memory Anchors and Partner Content

Metronidazole is an antibiotic used to treat many conditions caused by anaerobic bacteria or protozoans. Some bacterial infections include septicemia, endocarditis, and infections involving bone, joint, and the lower respiratory tract.

For these bacterial infections, metronidazole is administered intravenously. Metronidazole is also used to treat rosacea, for which it’s administered topically.

Finally, metronidazole is also used orally or topically to treat bacterial vaginosis; and it is used to treat protozoal infections, including amebiasis, trichomoniasis, and giardiasis, for which it’s given orally.

Now, once administered, metronidazole gets inside anaerobic bacteria and protozoans, and produces free radicals, which damage the pathogen’s DNA.

Without the DNA as a template, the pathogen can’t synthesize any more nucleic acids like DNA or mRNA, and will ultimately die.

Common side effects of metronidazole include headache, dizziness, and gastrointestinal disturbances like abdominal cramps, anorexia, nausea, vomiting, and diarrhea.

In addition, metronidazole may allow certain bacteria like Clostridioides difficile to survive and invade the gastrointestinal tract, rarely but potentially leading to Clostridioides difficile infection or CDI for short.

In high doses, or with prolonged treatment, it can cause a reddish urine, and neurological effects, such as seizures, confusion, and peripheral neuropathy can be seen; as well as aseptic meningitis, when given intravenously.

Other serious side effects include bone marrow suppression, which may result in leukopenia and thrombocytopenia.

Some clients on metronidazole may also develop a skin rash, urticaria, and phlebitis at the injection site, as well as severe hypersensitivity reactions like Stevens Johnson syndrome and toxic epidermal necrolysis. Metronidazole also has a boxed warning for carcinogenic potential.

Other side effects include irritability, insomnia, blurred vision, dry mouth, and metallic taste, as well as ECG changes like a flattening of a T wave.

Finally, clients on metronidazole that drink alcohol can also experience a disulfiram-like reaction, which presents with severe nausea, vomiting, and headaches.

As far as contraindications go, metronidazole shouldn’t be used during the first trimester of pregnancy and during breastfeeding, and precautions should be taken for the rest of the pregnancy.

It should also be used with caution in elderly clients, as well as in those with heart failure, fungal infections, and bone marrow suppression.

Additional precaution should be taken in clients with central nervous system disease, as well as in those with hematologic, gastrointestinal, renal, or hepatic disease.

Finally, unnecessary use of metronidazole should be avoided due to its carcinogenic potential, and that’s a boxed warning!

Regarding interactions, metronidazole shouldn’t be combined with medications like zalcitabine or disulfiram, as well as cimetidine, which increases the level and toxicity of metronidazole.

In addition, metronidazole is also metabolized in the liver and it’s a major substrate of the CYP2A6 enzyme, so it can interfere with the metabolism of certain medications, including warfarin, phenytoin, or lithium.

Finally, clients on metronidazole should avoid drinking alcohol, since it increases the risk of disulfiram-like reactions.