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Methylthioninium chloride (Methylene blue)
💉 Methylthioninium chloride (Methylene Blue) is the antidote for symptomatic methaemoglobinaemia. ⚠️ Always give slow IV and only if the patient remains symptomatic despite high-flow oxygen. 📋 Always check the BNF here for prescribing details.
🔬 Mode of Action
- Acts as a chemical reducing agent: ferric iron (Fe³⁺) in methaemoglobin → ferrous iron (Fe²⁺) in haemoglobin.
- First reduced to leucomethylene blue, which then restores haemoglobin function.
- Reduces the half-life of methaemoglobin from ⏱️ hours to just minutes.
💊 Indications & Dosing
- Drug- or chemical-induced methaemoglobinaemia – 👶 Child (3 months–17y): 1–2 mg/kg IV over 5 min; may repeat 1–2 mg/kg after 30–60 min (max 7 mg/kg/course). – 👩 Adult: same dosing (max 7 mg/kg/course).
- Aniline- or dapsone-induced methaemoglobinaemia – 👶 Child: 1–2 mg/kg IV over 5 min; repeat if needed, but max 4 mg/kg/course. – 👩 Adult: 1–2 mg/kg IV over 5 min; repeat if needed, max 4 mg/kg/course.
- ⚠️ Always seek advice from the National Poisons Information Service (NPIS) if further doses are considered.
⚠️ Side Effects
- 💢 Abdominal pain, chest pain, headache, dizziness, anxiety
- 🤢 Nausea, vomiting, altered taste
- 🖐️ Paraesthesia, pain in extremities
- 💦 Hyperhidrosis, skin reactions
- 🟦 Urine discolouration (blue/green)
📚 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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