Nidagyl (Metronidazole)

Metronidazole is used to treat infections caused by anaerobic bacteria and susceptible protozoa.

• Bacterial vaginosis: eradicates the anaerobic bacterial flora responsible for the condition, reducing symptoms and recurrence.
• Trichomoniasis: eliminates Trichomonas vaginalis, leading to cure of the infection and relief of genital irritation.
• Amoebiasis: destroys Entamoeba histolytica trophozoites, treating intestinal disease and preventing extra‑intestinal spread.
• Giardiasis: clears Giardia lamblia from the gastrointestinal tract, alleviating diarrhea and malabsorption.
• Anaerobic bacterial infections: targets anaerobes in intra‑abdominal, pelvic, skin and soft‑tissue infections, aiding clinical resolution.
• Clostridioides difficile infection (adjunct): used alongside standard therapy to reduce toxin production and support recovery.

• Metronidazole is a pro‑drug that enters susceptible microorganisms by passive diffusion. In anaerobic bacteria and protozoa, intracellular redox proteins reduce the nitro group to reactive nitro radicals. These radicals interact with DNA, causing strand breakage and loss of helical stability, and also inhibit nucleic acid synthesis, ultimately leading to cell death. The reduction process is minimal in aerobic cells, which limits toxicity to host tissues.

Metronidazole may cause a range of adverse reactions, varying from mild to severe.

Common Side Effects

• Nausea: mild to moderate stomach upset.
• Metallic taste: transient metallic sensation in the mouth.
• Diarrhea: loose stools that usually resolve after treatment.
• Headache: mild headache during therapy.
• Abdominal cramps: discomfort or cramping in the abdomen.
• Vomiting: occasional episodes of vomiting.
• Fatigue: feeling of tiredness.

Serious or Rare Side Effects

• Peripheral neuropathy: tingling or numbness in extremities, may be irreversible.
• Seizures: rare occurrence of convulsions.
• Severe allergic reaction: rash, itching, swelling, or difficulty breathing.
• Hepatotoxicity: elevated liver enzymes or jaundice.
• Blood dyscrasias: neutropenia, thrombocytopenia, or anemia.

Before prescribing Metronidazole, clinicians should consider several safety precautions to minimize risks.

• Assess liver function: evaluate hepatic status as the drug is metabolized hepatically.
• Review alcohol use: avoid alcohol during and at least 48 hours after therapy to prevent disulfiram‑like reaction.
• Monitor neurologic symptoms: watch for signs of peripheral neuropathy, especially with prolonged use.
• Evaluate renal function: dose adjustment may be needed in severe renal impairment.
• Pregnancy and lactation: use only if clearly needed; discuss potential risks with the prescriber.
• Store at ambient temperature: keep below 25 °C in the original container, protect from moisture and light.

Metronidazole can interact with other medicines, altering its effectiveness or increasing toxicity.

Major Interactions (Avoid)

• Alcohol: concurrent intake can cause severe flushing, tachycardia, nausea, and vomiting.
• Warfarin: may enhance anticoagulant effect, increasing risk of bleeding.
• Lithium: can raise lithium levels, leading to toxicity.

Moderate Interactions (Monitor Closely)

• Cimetidine: may increase metronidazole plasma concentrations.
• Phenobarbital: can reduce metronidazole levels, decreasing efficacy.
• Oral contraceptives: may have reduced effectiveness; advise additional contraceptive methods.
• Phenytoin: may lower metronidazole concentrations, requiring monitoring.
• Rifampin: induces hepatic enzymes, potentially decreasing metronidazole exposure.