Methylene Blue

Other Research Peptides

aka PROVAYBLUE · Methylthioninium chloride · Methylthionine chloride

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Formula

MW (Da)

Half-life

~5–6 hours

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Overview

Methylene blue is an oxidation-reduction thiazine dye. In the U.S., PROVAYBLUE is an FDA-approved methylene blue injection for methemoglobinemia. Low-dose mitochondrial or neurocognitive uses are widely discussed elsewhere, but the strongest evidence and clearest regulatory footing remain the approved hematologic indication.

Mechanism

The label states that methylene blue is reduced by NADPH reductase to leucomethylene blue, which then reduces ferric iron in methemoglobin back to the ferrous state of normal hemoglobin, restoring oxygen-carrying function. The same label carries an explicit warning about serotonin syndrome with serotonergic drugs and opioids, reflecting methylene blue's potent inhibition of monoamine oxidase A. Toxicity is strongly dose-related: cumulative dosing above clinical thresholds produces hemolysis, hypotension, neurologic effects, and visible blue staining of urine and tissues.

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Reported benefits

Approved therapy for acquired methemoglobinemia

PROVAYBLUE is FDA-approved for acquired methemoglobinemia. The reviewed prescribing information describes clinical-study use in 31 adults, with most administered doses being 1 mg/kg and the recommended dose fixed at that level.

[mb-dailymed-label]

clinical

Mechanism: reduces methemoglobin to functional hemoglobin

Methylene blue is reduced by NADPH reductase to leucomethylene blue, which converts ferric iron in methemoglobin (which cannot carry oxygen) back to the ferrous form of normal hemoglobin.

[mb-dailymed-label]

clinical

Reported side effects

Serotonin syndrome with serotonergic drugs and opioids
clinical
Methylene blue inhibits monoamine oxidase A. Combined with SSRIs, SNRIs, MAOIs, or opioids it can precipitate serotonin syndrome — a life-threatening drug interaction explicitly flagged on the label.
Hemolytic anemia in G6PD deficiency
clinical
Methylene blue can cause severe hemolytic anemia in patients with glucose-6-phosphate dehydrogenase (G6PD) deficiency. Hypersensitivity to thiazine dyes is also a recognized risk.
Dose-related cardiopulmonary and neurologic toxicity
clinical
Toxicity is dose-related. Single doses ≥3 mg/kg can cause hypotension, wheezing, and reduced oxygenation. Cumulative doses ≥7 mg/kg can produce nausea, vomiting, chest tightness, tachycardia, tremor, neurologic symptoms, and visible blue staining. Single doses ≥20 mg/kg have caused severe hemolysis and death.

Dosing notes

The FDA-approved dose is 1 mg/kg IV over 5–30 minutes. If methemoglobin remains above 30% or symptoms persist, one repeat dose of up to 1 mg/kg may be given 1 hour later. In moderate or severe renal impairment, the label recommends a single 1 mg/kg dose and consideration of alternative interventions if the patient remains severely affected. Dilution, when needed, is in 5% dextrose (not saline) and the diluted solution is used immediately.

Research use only. Information on this page is editorial reference, not medical or dosing advice. Always consult qualified medical guidance before use.

Storage

Store at 20-25°C, with excursions to 15-30°C; do not refrigerate or freeze; keep the ampule or vial in the original package to protect from light.

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Discussion

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References

[mb-dailymed-label]
PROVAYBLUE (methylene blue injection) U.S. Prescribing Information
Manufacturer per DailyMed entry · DailyMed
Source

Reported benefits

Approved therapy for acquired methemoglobinemia

Mechanism: reduces methemoglobin to functional hemoglobin

Serotonin syndrome with serotonergic drugs and opioids

Hemolytic anemia in G6PD deficiency

Dose-related cardiopulmonary and neurologic toxicity

Discussion