Methylene Blue

Provider Level

RN/Paramedic

Class

Antidote, oxidation-reduction agent

Mechanism of Action

Accelerates the enzymatic reduction of methemoglobin to hemoglobin, restoring normal oxygen-carrying capacity. Acts as a cofactor for the enzyme NADPH-methemoglobin reductase.

Indications

Symptomatic methemoglobinemia presenting with hypoxia unresponsive to oxygen therapy, severe cyanosis, or altered mental status, typically induced by agents like nitrites or local anesthetics.

Contraindications

Known hypersensitivity, glucose-6-phosphate dehydrogenase (G6PD) deficiency due to risk of hemolytic anemia, severe renal impairment, and known cyanide poisoning (unless specifically treating concurrent methemoglobinemia).

Routes

IV, IO

Onset / Duration

Onset: 30 to 60 minutes. Duration: Variable depending on the half-life of the causative oxidizing agent.

Adverse Effects

Nausea, vomiting, headache, dizziness, confusion, chest pain, tachycardia, hypertension, diaphoresis, and bluish discoloration of the skin, mucous membranes, and urine.

Precautions & Interactions

Can cause transient but profound false drops in pulse oximetry readings due to its blue color. Extravasation can lead to severe local tissue necrosis. High risk of serotonin syndrome if administered to patients taking SSRIs, SNRIs, or MAOIs.

Special Considerations

Flush the IV line thoroughly before and after administration. Monitor clinical signs of oxygenation rather than relying solely on pulse oximetry. Monitor for signs of hemolysis, especially in patients with unknown G6PD status.