Metronidazole Substipharm (Metronidazole)

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

• Bacterial vaginosis: restores normal vaginal flora by eliminating anaerobic overgrowth.
• Trichomoniasis: eradicates Trichomonas vaginalis, relieving symptoms and preventing recurrence.
• Amoebiasis: destroys intestinal Entamoeba histolytica trophozoites, aiding cure of dysentery.
• Giardiasis: eliminates Giardia lamblia, reducing diarrhea and malabsorption.
• Anaerobic bacterial infections: targets a broad range of anaerobes in intra‑abdominal, skin and dental infections.
• Clostridioides difficile infection: suppresses toxin‑producing C. difficile, helping resolve colitis.

• Metronidazole is taken up by anaerobic microorganisms and reduced by intracellular electron transport proteins to generate reactive nitro radical anions. These anions covalently bind to DNA, causing strand breakage and inhibition of nucleic acid synthesis, which leads to bacterial and protozoal cell death while sparing aerobic cells.

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

Common Side Effects

• Nausea: mild to moderate upset stomach.
• Metallic taste: persistent metallic sensation in the mouth.
• Headache: transient cranial discomfort.
• Diarrhea: loose stools, usually self‑limiting.
• Abdominal pain: cramping or discomfort in the abdomen.
• Loss of appetite: reduced desire to eat.

Serious or Rare Side Effects

• Seizures: convulsive episodes, especially with high plasma levels.
• Peripheral neuropathy: tingling or numbness in extremities.
• Severe allergic reaction: anaphylaxis with rash, swelling, and breathing difficulty.
• Stevens‑Johnson syndrome: severe skin and mucous membrane eruption.
• Liver toxicity: elevated transaminases or hepatitis.
• Pancytopenia: reduction of red cells, white cells, and platelets.

When prescribing Metronidazole, several safety considerations should be observed.

• Pregnancy: safety not established; use only if benefits outweigh potential risks.
• Alcohol: avoid concurrent consumption to prevent a disulfiram‑like reaction.
• Renal impairment: dose adjustment may be required in severe dysfunction.
• Hepatic disease: monitor liver function tests during therapy.
• Drug interactions: review concomitant medications for potential interactions.
• Store at ambient temperature: keep in the original container, protect from moisture and light.

Metronidazole can interact with other medicines, influencing efficacy or safety.

Major Interactions (Avoid)

• Alcohol: may cause severe flushing, tachycardia, and hypotension.
• Warfarin: increased anticoagulant effect, raising bleeding risk.
• Lithium: heightened lithium toxicity due to reduced clearance.
• Cimetidine: may raise metronidazole plasma concentrations.

Moderate Interactions (Monitor Closely)

• Phenytoin: may reduce metronidazole levels, decreasing efficacy.
• Phenobarbital: may lower metronidazole concentrations.
• Carbamazepine: may accelerate metronidazole metabolism.