From the Guidelines
Methylene blue is primarily used as a treatment for methemoglobinemia, with a recommended dose of 1-2 mg/kg administered intravenously over 5 minutes, as supported by the most recent guidelines 1.
Indications and Uses
The primary indication for methylene blue is the treatment of methemoglobinemia, a condition where the blood cannot properly carry oxygen due to altered hemoglobin structure.
- It works by providing an alternative electron acceptor for NADPH methemoglobin reductase, converting methemoglobin back to hemoglobin.
- Beyond this primary use, methylene blue serves as a surgical dye for tissue marking and visualization during procedures like sentinel lymph node mapping, typically at concentrations of 1% 1.
- It's also used to treat ifosfamide-induced encephalopathy at doses of 50 mg IV every 4 hours until symptoms resolve.
- In urological procedures, it helps identify ureteral patency and vesicoureteral reflux.
- Additionally, methylene blue can be used as a vasopressor in refractory septic shock (1-2 mg/kg IV), functioning as a nitric oxide synthase inhibitor.
- It's occasionally employed for the treatment of certain poisonings, particularly cyanide toxicity, and has been investigated for use in psychiatric conditions.
Precautions and Considerations
Important precautions include avoiding use in patients with G6PD deficiency due to risk of hemolysis, and being aware of potential serotonin syndrome when combined with serotonergic medications 1.
- Methylene blue should be used with caution in pregnant women because of concerns about teratogenicity, and possible intestinal atresia.
- It should also be used cautiously in patients with renal failure and in anesthetized patients where it may inhibit guanylate cyclase, decreasing nitric oxide-mediated vasodilatation leading to systemic and pulmonary hypertension.
- In cases of methemoglobinemia not responsive to methylene blue, exchange transfusion or hyperbaric oxygen therapy may be considered as alternative treatments 1.
From the FDA Drug Label
The FDA drug label does not answer the question.
From the Research
Methylene Blue Indications
- Methylene blue is used to treat methemoglobinemia, a condition characterized by an abnormal amount of methemoglobin in the blood, at a dose of 1 to 2 mg/kg intravenously 2.
- It is also used to treat refractory hypotension, particularly in cases of vasoplegic shock, with a loading dose of 1 mg/kg followed by a continuous infusion at 0.25 mg/kg per hour 3.
- Additionally, methylene blue has been used to treat neuropsychiatric disorders, including depression, anxiety, and bipolar disorder, due to its antidepressant, anxiolytic, and neuroprotective properties 4.
Mechanism of Action
- Methylene blue works by interacting with methemoglobin and the erythrocyte's enzyme systems to reduce back to hemoglobin, thereby treating methemoglobinemia 2.
- It also has an inhibitory effect on monoamine oxidase A, which can lead to serotonin toxicity when combined with serotonin reuptake inhibitors 5.
- Methylene blue's mechanism of action is complex and based partly on its oxidizing capabilities, which can be both beneficial and harmful depending on the context 6.
Uses Beyond Methemoglobinemia
- Methylene blue has been used to treat ifosfamide neurotoxicity and refractory vasoplegic shock in both pediatric and adult critical care patients 6.
- It has also been used as an aid to parathyroidectomy and to treat psychotic and mood disorders 5.
- Methylene blue's potential uses are still being explored, and it may have applications in the treatment of other conditions, such as organic/neurodegenerative disorders 4.