From the Guidelines
Methylene blue is primarily used to treat methemoglobinemia, and its recommended dose is 1–2 mg/kg infused intravenously over 3 to 5 minutes, as supported by the American Journal of Hematology in 2021 1. The use of methylene blue is critical in decreasing MetHb levels, acting by accepting an electron from NADPH and reducing the 3+ ferric state back to the 2+ ferrous state in erythrocytes. Key points to consider when using methylene blue include:
- The dose may be repeated at 1 mg/kg if methemoglobinemia does not significantly decrease within 30–60 minutes 1.
- Risk of worsening of methemoglobinemia increases with repeated doses, with toxic levels of MB reached at a total dose > 7 mg/kg 1.
- A rebound phenomenon of increased MetHb levels after completion of therapy is attributed to the reversal of the reduction reaction, and in cases of worsening methemoglobinemia after MB treatment, urgent exchange transfusion should be performed 1.
- For patients with continued production of MetHb from a long-acting oxidant stress, repeat dosing every 6–8 hours for up to 2–3 days or a continuous IV infusion of 0.10–0.25 mg/kg/hr may be necessary 1. Considering the potential risks and benefits, the primary treatment for methemoglobinemia with methylene blue should be initiated promptly, with careful monitoring of the patient's response to the treatment and adjustment of the dose as needed, based on the most recent guidelines from 2021 1.
From the Research
Uses of Methylene Blue
- Methylene blue is used to treat methemoglobinemia, a disorder characterized by the presence of >1% methemoglobin in the blood 2, 3, 4.
- It acts by providing an artificial electron acceptor for NADPH methemoglobin reductase, which helps to reduce methemoglobin back to hemoglobin 2.
- The typical dose of methylene blue for treating methemoglobinemia is 1-2 mg/kg administered slow intravenously 2, 3, 4.
- Methylene blue is also used as a prophylactic regimen to prevent ifosfamide-induced encephalopathy, a potential side effect of ifosfamide chemotherapy 5.
- In this context, methylene blue is often used in combination with hydration and thiamine to prevent encephalopathy 5.
Important Considerations
- Methylene blue should be used with caution in patients with known or suspected glucose-6-phosphate dehydrogenase (G6PD) deficiency, as it can exacerbate hemolysis in these patients 2, 3, 4.
- The effectiveness of methylene blue may be reduced in patients with G6PD deficiency or haemolysis 4.
- Alternative treatment options, such as hyperbaric oxygenation monotherapy, may be considered when methylene blue is not available or effective 6.