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methylthioninium chloride
V03AB17
Forms & Strengths
- Injectable solution 1% (10 mg/mL) for IV/IM use
- Injectable solution 10% (100 mg/mL) for IV use
- Oral tablets 100 mg and 150 mg
- Ophthalmic solution 0.1% for urinary tract infections
Adult Dosing
- Methemoglobinemia: 1–2 mg/kg IV over 5 min (max total 7 mg/kg), repeat q1h if needed
- Methemoglobinemia oral: 1–2 mg/kg single dose, may repeat once
- Cyanide poisoning (as part of kit): 1–2 mg/kg IV bolus, followed by 0.5 mg/kg q1h up to 5 mg total
- Ifosfamide‑induced encephalopathy: 50 mg IV q6h for 2 days (max 200 mg)
- Urinary antisepsis: 100 mg PO daily for 5 days
Pediatric Dosing
- Methemoglobinemia: 1–2 mg/kg IV over 5 min (max total 7 mg/kg), repeat q1h if needed
- Methemoglobinemia oral: 1–2 mg/kg single dose, may repeat once
- Cyanide poisoning: 1 mg/kg IV bolus (max 5 mg total), may repeat q1h
- Ifosfamide encephalopathy: 25 mg IV q6h for 48 h (dose weight‑adjusted)
- Urinary antisepsis: 50 mg PO daily (age‑appropriate) for 5 days
Indications
- Acute acquired methemoglobinemia
- Cyanide poisoning (in combination with sodium nitrite)
- Ifosfamide‑induced neurotoxicity
- Urinary tract antisepsis (off‑label)
- Diagnostic stain for surgical procedures
Mechanism of Action
- Acts as an artificial electron carrier, reducing Fe3+ (methemoglobin) to Fe2+ (hemoglobin)
- Inhibits nitric‑oxide synthase and guanylate cyclase, producing vasoconstriction
- Enhances mitochondrial respiration in ifosfamide neurotoxicity
- Provides antiseptic effect via oxidative damage to bacterial cell walls
Contraindications
- Severe G6PD deficiency (risk of hemolysis)
- Known hypersensitivity to methylene blue or related dyes
- Concurrent use of potent serotonergic agents when high doses required
Adverse Reactions
- Blue‑green discoloration of urine, sclera, and skin
- Hemolysis in G6PD‑deficient patients
- Serotonin syndrome when combined with SSRIs, MAOIs, linezolid, tramadol, etc.
- Hypertension, tachycardia, chest pain
- Nausea, vomiting, abdominal cramps
- Rare paradoxical methemoglobinemia at high doses
Drug Interactions
- SSRIs, SNRIs, MAO inhibitors, linezolid, tramadol, dextromethorphan → increased serotonin syndrome risk
- Phenothiazines and other MAO‑inhibiting agents → potentiated hypertensive response
- Cyanide antidote regimen (sodium nitrite) – synergistic methemoglobin formation
- Laboratory assays: interferes with pulse‑oximetry and colorimetric tests
- Potential reduction of efficacy of antihypertensives metabolized by CYP2D6
Curated Content: Needs Vetting Before Put to Clinical Use