METHYLTHIONINIUM CHLORIDE (METHYLENE BLUE)

Antidote for methaemoglobinaemia

Dosage Forms

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Injection

10 mg/ml

Uses

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  • Acute methaemoglobinaemia

Dose and Duration

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Acute methaemoglobinaemia

Adult and child over 3 months: by slow IV injection over 5 minutes, 1–2 mg/kg as a single dose.

Neonate and child below 3 months: by IV injection over 5 minutes, 0.3–0.5 mg/kg.

Repeat dose after 1 hour if necessary (max cumulative dose 7 mg/kg or 4 mg/kg in aniline- or dapsone-induced methaemoglobinaemia)

Contraindications

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  • Methaemoglobinaemia due to chlorate or due to sodium nitrite in treatment of cyanide poisoning
  • Deficiency of nicotinamide adenine dinucleotide phosphate-oxidase (NADPH) reductase enzyme

Side Effects

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  • Nausea, vomiting, abdominal pain
  • Hyperbilirubinaemia in infants
  • Chest pain, dyspnoea
  • Headache, dizziness, confusion
  • Tachycardia, hypertension, hypotension, arrhythmias

Interactions

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  • Clomipramine, fluoxetine, sertraline, citalopram, fluvoxamine, venlafaxine, duloxetine: (risk of CNS toxicity)
  • Mirtazapine, bupropion, buspirone: (possible risk of CNS toxicity)

Pregnancy

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  • Can be used

Breast-feeding

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  • Do not use

⚠️ Caution

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  • Use with caution in moderate to severe renal disease, and in G6PD deficiency due to risk of haemolytic anaemia
  • Monitor blood methaemoglobin during treatment
  • Avoid breast-feeding for up to 8 days after administration of methylthioninium chloride
  • Only use in pregnancy when it is clearly necessary