From the Guidelines
Methylene blue is a crucial medication in medical practice, primarily used as a first-line treatment for methemoglobinemia, administered at 1-2 mg/kg intravenously, as supported by recent evidence 1.
Uses of Methylene Blue
- Treatment of methemoglobinemia: Methylene blue acts by reducing methemoglobin to oxyhemoglobin in erythrocytes, with a usual starting dose of 1–2 mg/kg infused intravenously over 3 to 5 minutes 1.
- Surgical settings: It functions as a vital dye for tissue visualization, particularly in sentinel lymph node mapping during cancer surgeries and for identifying urinary tract structures.
- Treatment of vasoplegic syndrome: Methylene blue is used at doses of 1-2 mg/kg followed by continuous infusion if needed, to increase vascular tone in hypotensive conditions.
- Antimicrobial properties: It is used to treat urinary tract infections and as a topical antiseptic.
Administration and Precautions
- The dose may be repeated at 1 mg/kg if methemoglobinemia does not significantly decrease within 30–60 minutes, with a risk of worsening methemoglobinemia with repeated doses 1.
- Patients with G6PD deficiency are at risk for complications after methylene blue administration, including hemolytic anemia, and should be tested for G6PD deficiency before treatment 1.
- Methylene blue should be used with caution in pregnant women, patients with renal failure, and anesthetized patients, due to concerns about teratogenicity, hemolysis, and inhibition of guanylate cyclase 1.
Mechanism of Action
- Methylene blue reduces methemoglobin by providing an alternative electron acceptor, creates visible staining through its blue color properties, and inhibits nitric oxide synthase to increase vascular tone in hypotensive conditions.
- Potential side effects include blue discoloration of skin and urine, hemolytic anemia in G6PD-deficient patients, and serotonin syndrome when combined with certain psychiatric medications 1.
From the FDA Drug Label
PACKAGE LABEL.PRINCIPAL DISPLAY PANEL NDC 70771-1768-1 Methylene Blue Injection, USP 50 mg/10 mL (5 mg/mL) Intravenous use only Single-Dose vial Rx only The FDA drug label does not answer the question.
From the Research
Medical Uses of Methylene Blue
Methylene blue has several uses in medical practice, including:
- Treatment of acquired methemoglobinemia (MetHB) 2
- Treatment of ifosfamide neurotoxicity 2, 3, 4
- Treatment of refractory vasoplegic shock in pediatric and adult patients 2, 5
- Diagnostic tool in surgical procedures 3
- Potential treatment for distributive shock, including sepsis and anaphylaxis 6
- Treatment of ifosfamide-induced encephalopathy (IIE) 3, 4
Mechanism of Action and Side Effects
Methylene blue's mechanism of action is complex and based partly on its oxidizing capabilities 2. It can also act as a selective inhibitor of the NO-cGMP pathway, which plays a role in the pathophysiology of distributive shock 6. However, methylene blue can also induce serotonin syndrome, especially when used in conjunction with other serotonergic agents 5, 4.
Specific Applications
Methylene blue has been used in various areas of medicine, including: