Although not used currently, large doses of methylene blue can be used to treat potassium cyanide poisoning (method first tested in 1933 by Dr. Matilda Moldenhauer Brooks, San Francisco)
The reduction potential of methylene blue is similar to oxygen and can be reduced by the electron transport chain
Use of Other Serotonergic Agents (see Serotonin Syndrome, [[Serotonin Syndrome]]): as the combination may precipitate serotonin syndrome (see Serotonin Syndrome, [[Serotonin Syndrome]])
Pharmacology
Methylene Blue Functions as a Reducing Agent: at pharmacologic doses (however, can act as an oxidizing agent at very high doses)
Normally, methemoglobin is reduced back to hemoglobin by NADH/NADPH-dependent methemoglobin reductase enzymes -> however, with large amounts of methemoglobin, these reductases are overwhelmed
Methylene Blue (IV): methylene blue is reduced to leucomethylene blue -> subsequently, reduces the heme group from methemoglobin to hemoglobin
Methylene Blue Functions as a Reversible Monoamine Oxidase (MAO) Inhibitor (see Monoamine Oxidase Inhibitors, [[Monoamine Oxidase Inhibitors]]): MAO normally degrades serotonin in the brain
FDA Alert (7/26/11): avoid use in conjunction with SSRI’s
Methylene Blue is Structurally Similar to the Chlorpromazine and the Typical Antipsychotics
Methylene blue is the substrate from which chlorpromazine and many other antipsychotics are synthesized
Administration
Dosing (for Methemoglobinemia): 1-2 mL/kg (of 1% solution) IV over 5 min
Methylene blue is less effective and may exacerbate hemolysis in patients with G6PD deficiency (G6PD deficient cells clear methemoglobin slowly in response to methylene blue) -> use cautiously in these patients
Toxicologic Adverse Effects
Methemoglobinemia (see Methemoglobinemia, [[Methemoglobinemia]]): although methylene blue is used to treat methemoglobinemia, at high doses, it can also paradoxically cause methemoglobinemia
