From the Guidelines
Methylene blue is a synthetic dye that functions as a medication, primarily working as a reducing agent to treat methemoglobinemia by converting abnormal methemoglobin back to normal hemoglobin at doses of 1-2 mg/kg intravenously. It acts by accepting an electron from NADPH, and, in its new form, leukomethylene blue acts to reduce the 3+ ferric state back to the 2+ ferrous state in erythrocytes 1. The usual starting dose is 1–2 mg/kg (0.2 mL/kg of a 1% solution) infused intravenously over 3 to 5 minutes, and the dose may be repeated at 1 mg/kg if methemoglobinemia does not significantly decrease within 30–60 minutes 1.
Some key points to consider when using methylene blue include:
- The 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 1
- In cases of worsening methemoglobinemia after MB treatment, urgent exchange transfusion should be performed 1
- Patients with continued production of MetHb from a long-acting oxidant stress may require repeat dosing every 6–8 hours for up to 2–3 days or MB may be given as a continuous IV infusion of 0.10–0.25 mg/kg/hr 1
It is essential to carefully monitor patients receiving methylene blue, as higher doses may cause hemolysis, particularly in patients with G6PD deficiency. Additionally, methylene blue can cause temporary blue-green discoloration of urine and skin and may interfere with pulse oximeter readings. Overall, methylene blue is a valuable medication for treating methemoglobinemia, but its use requires careful consideration of the potential risks and benefits.
From the Research
What is Methylene Blue
- Methylene blue is a drug that has been in medicinal use for centuries, primarily known for its antidotal treatment of acquired methemoglobinemia (MetHB) 2.
- It is also used to treat ifosfamide neurotoxicity and refractory vasoplegic shock in both pediatric and adult critical care patients 2.
Mechanism of Action
- Methylene blue's mechanism of action is complex and based partly on its oxidizing capabilities, which is the same mechanism that causes MetHB 2.
- It interacts with methemoglobin and the erythrocyte's enzyme systems to reduce back to hemoglobin, making it a generally safe drug with dose-related hemolytic effects 3.
Treatment of Methemoglobinemia
- Methylene blue is used to treat methemoglobinemia, a condition where the hemoglobin in the blood is oxidized, leading to a decrease in the ability of the blood to carry oxygen 4.
- The treatment of methemoglobinemia with methylene blue is effective in reducing the level of methemoglobin in the blood, with a dose of 1 to 2 mg/kg intravenously being commonly used 3.
- Other treatments for methemoglobinemia include intravenous administration of ascorbic acid and riboflavin 5.
Special Considerations
- People with G-6-PD deficiency, as well as patients exposed to aniline dyes and dapsone, may present with special risks in the treatment of methemoglobinemia with methylene blue 3.
- In patients with a deficit of glucoso-6-phosphate-dehydrogenase, the administration of methylene blue is contraindicated, as it can worsen methemoglobinemia 4.
Comparison with Other Treatments
- Methylene blue has been compared to other treatments for methemoglobinemia, such as riboflavin and N-acetylcysteine, and has been shown to be effective in reducing the level of methemoglobin in the blood 6.
- The use of methylene blue has been shown to be superior to other treatments in some cases, with a faster reduction in methemoglobin levels and a lower risk of side effects 6.