Drug-induced methemoglobinemia (systemic, not an ocular use)
0.1 to 0.2 mL/kg of the 1% solution IV, injected very slowly over several minutes
Contraindications
Pregnancy or possible pregnancy; teratogen, with ileal and jejunal atresia and ileal occlusion reported after use in amniocentesis
Intraspinal or subcutaneous injection
Known hypersensitivity to methylene blue
Available Forms
1% injection (10 mg/mL), 2 mL single-dose prefilled syringes, cartons of five.
Mechanism of Action
Low concentrations reduce methemoglobin back to hemoglobin, while high concentrations oxidize ferrous iron to ferric and generate methemoglobin; metabolism is to leukomethylene blue, excreted mainly in urine. It is also a potent monoamine oxidase inhibitor, which is the basis of the serotonin toxicity risk.
Warnings & Precautions
Serotonin syndrome: Boxed warning. Serious or fatal serotonergic reaction with SSRIs, SNRIs, or monoamine oxidase inhibitors; avoid concomitant use.
Serotonergic drug interactions: Tricyclics, norepinephrine-dopamine reuptake inhibitors, triptans, and ergot alkaloids carry the same risk of fatal serotonin toxicity; any serotonin reuptake inhibitor must be stopped before treatment.
G6PD deficiency: Paradoxical methemoglobinemia and hemolysis; avoid.
Rapid injection: Local high concentration produces additional methemoglobin, so the dose is given over several minutes.
Severe renal impairment: Caution advised.
Common Side Effects
Systemic, large IV doses: Nausea, abdominal and precordial pain, dizziness, headache, profuse sweating, mental confusion, and methemoglobin formation.
Serotonin toxicity: Tremor, clonus, myoclonus, hyperreflexia, and pyramidal rigidity when advanced; diaphoresis, fever, tachycardia, tachypnea, mydriasis; agitation, excitement, and confusion.
Pregnancy & Lactation
Pregnancy: Contraindicated. Category X teratogen; ileal and jejunal atresia and ileal occlusion reported in neonates after use in amniocentesis.
GoodRx
Available Forms
Mechanism of Action
Pregnancy & Lactation
Pediatric Use