Methylene blue

Therapeutic Class
 Antidote
Indications

Antidote for cyanide poisoning and drug-induced methemoglobinemia, indicator dye.

Unlabeled/Investigational: Treatment/prevention of ifosfamide-induced encephalopathy; topically, in conjunction with polychromatic light to photoinactivate viruses such as herpes simplex; alone or in combination with vitamin C for the management of chronic urolithiasis.
Adult Doses

I.V.:

Methemoglobinemia: 1-2 mg/kg or 25-50 mg/m2 over 5-10 minutes; may be repeated in 1 hour if necessary.
Ifosfamide-induced encephalopathy (unlabeled use):
Prevention: 50 mg every 6-8 hours
Treatment: 50 mg as a single dose or every 4-8 hours until symptoms resolve
Contraindications

Hypersensitivity to methylene blue or any component of the formulation; intraspinal injection; renal insufficiency.
Warnings / Precautions

Anemia, Methemoglobinemia, Renal impairment, Serotonin modulators, G6PD deficiency, Young patients, Do not inject SubQ or intrathecally ,should not be added to enteral feeding products.
Adverse Reactions

Cardiovascular: Hypertension, precordial pain

Central nervous system: Dizziness, headache, fever, mental confusion

Dermatologic: Staining of skin

Gastrointestinal: Abdominal pain, fecal discoloration (blue-green), nausea, vomiting

Genitourinary: Bladder irritation, discoloration of urine (blue-green)

Hematologic: Anemia, transient reduction in oxygen saturation as read by pulse oximetry

Miscellaneous: Diaphoresis, Serotonin syndrome
Mechanism of Actions

Weak germicide in low concentrations, hastens the conversion of methemoglobin to hemoglobin; has opposite effect at high concentrations by converting ferrous ion of reduced hemoglobin to ferric ion to form methemoglobin; in cyanide toxicity, it combines with cyanide to form cyanmethemoglobin preventing the interference of cyanide with the cytochrome system.
Pharmacodynamics

Onset of action: Reduction of methemoglobin: I.V.: 30-60 minutes

Absorption: Oral: 53% to 97%

Metabolism: Peripheral reduction to leukomethylene blue

Excretion: In bile, feces, and urine as leukomethylene blue
Monitoring

Arterial blood gases; cardiac monitoring (patients with pre-existing pulmonary and/or cardiac disease); CBC; methemoglobin levels (co-oximetry yields a direct and accurate measure of methemoglobin levels); pulse oximeter (will not provide accurate measurement of oxygenation when methemoglobin levels are >35%); renal function; signs and symptoms of methemoglobinemia such as pallor, cyanosis, nausea, muscle weakness, dizziness, confusion, agitation, dyspnea, and tachycardia; transcutaneous O2 saturation
Administration

I.V.: Administer undiluted by direct I.V. injection over 5-10 minutes.

Consider concomitant dextrose administration, especially in patients who are hypoglycemic, to ensure efficacy of methylene blue.
Pregnancy Category

C: Drug Pregnancy Category Animal reproduction studies have shown an adverse effect on the fetus and there are no adequate and well-controlled studies in humans, but potential benefits may warrant use of the drug in pregnant women despite potential risks.
ATC Classification
 V03AB17,V04CG05
GenericPedia Classification

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