Methylene blue

Administration

• Type: Antidote, Vasopressors
• Routes of Administration: IV

Adult Dosing

• Acquired methemoglobinemia: 1 mg/kg IV over 5-30min, may repeat in 1h with up to 1 mg/kg IV if methemoglobin level still >30% or symptoms persist
• Drug-induced methemoglobinemia: 1-2 mg/kg IV slowly over several minutes
• See vasopressors
  • For hypotension refractory to catecholamine pressors
  • Consider after catecholamine, vasopressin, and mineralocorticoid refractive shock

Pediatric Dosing

• Same as weight-based adult dosing

Special Populations

• Pregnancy Rating: X, Fetal risk has been demonstrated
• Lactation risk: Infant risk cannot be ruled out
• Renal dosing: no adjustment
• Hepatic dosing: no adjustment

Contraindications

• Allergy to class/drug
• G6PD deficiency
• ARDS
• Pulmonary hypertension

Adverse Reactions

Serious

• Hemolytic anemia
• Syncope
• Serotonin syndrome
• Paradoxical methemoglobinemia at doses > 4 mg/kg/hr or per bolus
• Pulmonary vasoconstriction at 3-4 mg/kg/hr or per bolus

Common

• Skin discoloration, urine discoloration, hyperhidrosis
• Nausea, abnormal taste
• Limb pain
• Dizziness, headache

Pharmacology

• Half-life: 24h
• Metabolism: Hepatic
• Excretion: Mostly renal

Mechanism of Action

• Promotes non-enzymatic redox conversion of methemoglobin to hemoglobin
• Improves vascular tone via inhibition of nitric oxide synthase

See Also

• Methemoglobinemia
• Antidotes