What is the role of methylene blue in the treatment of methemoglobinemia?

Updated: Dec 09, 2018
  • Author: Mary Denshaw-Burke, MD, FACP; Chief Editor: Emmanuel C Besa, MD  more...
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Answer

Methylene blue is the primary emergency treatment for documented symptomatic methemoglobinemia. It is given in a dose of 1-2 mg/kg (up to a total of 50 mg in adults, adolescents, and older children) as a 1% solution in IV saline over 3-5 minutes. Administration may be repeated at 1 mg/kg every 30 minutes as necessary to control symptoms. Methylene blue is itself an oxidant at doses greater than 7 mg/kg and thus may cause methemoglobinemia in susceptible patients; hence, careful administration is essential.

Methylene blue is contraindicated in patients with G6PD deficiency. Because it requires G6PD to work, it is ineffective in G6PD-deficient patients with methemoglobinemia. Additionally, methylene blue administration may cause hemolysis in these patients.

Methylene blue is also not effective in patients with hemoglobin M (Hb M). Other conditions in which methylene blue may be ineffective or even deleterious include nicotinamide adenine dinucleotide phosphate (NADPH) methemoglobin reductase (ie, diaphorase II) deficiency and sulfhemoglobinemia.

The US Food and Drug Administration (FDA) warns against using methylene blue concurrently with serotonergic psychiatric drugs, unless such usage is indicated for life-threatening or urgent conditions. Methylene blue may increase central nervous system (CNS) serotonin levels as a result of monoamine oxidase (MAO)-A inhibition, thus increasing the risk of serotonin syndrome. [62]


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