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Metronidazole (Flagyl)
💊 Must be given orally for pseudomembranous colitis with Clostridioides difficile infection, as it acts within the bowel lumen.
📖 About
Always check the BNF link here.
- ⚡ Nitroimidazole antibiotic.
- 🦠 Highly effective against anaerobic bacteria and some protozoa.
⚙️ Action
- 🔬 Reduced within anaerobic cells to toxic metabolites that disrupt DNA and bacterial metabolism.
🌍 Activity
- ✅ Anaerobes including Bacteroides fragilis.
- ✅ Protozoa: Trichomonas vaginalis, Entamoeba histolytica, Giardia lamblia.
- ✅ Clostridium tetani and Clostridioides difficile.
📊 Dose Range (check BNF / datasheet)
| Indication | Dose | Frequency | Route |
|---|---|---|---|
| Mild infection | 400 mg | 8-hourly | PO |
| C. difficile | 400–500 mg | 8-hourly | PO |
| Trichomonas | 250 mg | 8-hourly (7 days) | PO |
| Giardiasis | 2 g | once daily (3 days) | PO |
| Giardiasis | 400 mg | 8-hourly (5 days) | PO |
| Amoebiasis | 800 mg | 8-hourly (5–10 days) | PO |
| Fistulating Crohn’s | 400–500 mg | 8-hourly (1 month) | PO |
| Moderate/Severe infection | 500 mg | 8-hourly | IV |
🔄 Interactions
- 🍷 Disulfiram-like reaction with alcohol → flushing, abdominal pain, hypotension.
- ⚠️ Inhibits warfarin metabolism → ↑ INR.
- 📈 Can increase lithium and phenytoin toxicity.
- 🚫 Avoid in porphyria.
⚠️ Cautions
- 🧠 Prolonged use (>4 weeks) may cause peripheral neuropathy.
- 🤰 Use with caution in pregnancy and breastfeeding (seek specialist advice).
- 🚫 Porphyria.
⛔ Contraindications
- 📌 Specialist advice required in pregnancy, breastfeeding, and porphyria.
💥 Side Effects
- 🤢 GI: nausea, vomiting, diarrhoea, metallic taste.
- 🧪 Hepatic: hepatitis (rare).
- 🧠 CNS: headache, seizures (at high doses).
- 🦶 Sensory neuropathy with prolonged treatment.
📚 References
| The content on this website is provided for educational and informational purposes only to support exam preparation (e.g., MLA, MRCP, USMLE) and learning. This is NOT medical advice, diagnosis, treatment, or professional guidance. It does not replace consultation with a qualified healthcare professional, official guidelines (e.g., NICE, GMC, BNF), or supervised clinical practice. Always verify information with current, authoritative sources. Makindo and its contributors accept no liability for any reliance on this content, including errors, omissions, or any resulting harm, loss, or consequences. By using this site, you agree to these terms. |
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