Methylene blue therapy can precipitate the Serotonin Syndrome in patients taking a serotonergic drug.
Methylene blue is used in the emergency therapy of:
(1) methemoglobinemia
(2) ifosfamide-induced encephalopathy
(3) cyanide poisoning
Methylene blue can act as a monoamine oxidase inhibitor (MAOI). Monoamine oxidase breaks down serotonin, so inhibition of the enzyme can result in an accumulation of serotonin to toxic levels within the brain.
In general a patient taking a serotonergic drug should not receive methylene blue. Usually a person taking a serotonergic antidepressant needs to stop the drug 2 weeks before exposure to methylene blue (5 weeks for fluoxetine because of the long half-life). However, in an ermergency situation it may be necessary to treat the patient with methylene blue despite the risk.
The onset of unexpected central nervous system symptoms (change in mental status, agitation, hyperarousal, myoclonus, hyperreflexia, diaphoresis, tremor, oculgyric crisis, high fever) during methylene blue therapy should raise the possibility of the serotonin syndrome.
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