Methylene blue
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| Trade names | Urelene blue, Provayblue, Proveblue, other |
| AHFS/Drugs.com | Monograph |
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| Routes of administration |
by mouth, IV |
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| Synonyms | CI 52015 |
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| ChEMBL | |
| ECHA InfoCard | 100.000.469 |
| Chemical and physical data | |
| Formula | C16H18ClN3S |
| Molar mass | 319.85 g/mol |
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Methylene blue, also known as methylthioninium chloride, is a medication and dye. As a medication it is mainly used to treat methemoglobinemia. Specifically it is used to treat methemoglobinemia levels that are greater than 30% or in which there are symptoms despite oxygen therapy. It has previously been used for cyanide poisoning and urinary tract infections but this use is no longer recommended. It is typically given by injection into a vein.
Common side effects include headache, vomiting, confusion, shortness of breath, and high blood pressure. Other side effects include serotonin syndrome, red blood cell breakdown, and allergic reactions. Use often turns the urine, sweat, and stool blue to green in color. While use during pregnancy may harm the baby, not using in methemoglobinemia is likely more dangerous. Methylene blue is a thiazine dye. It works by converting the ferric iron in hemoglobin to ferrous iron.
Methylene blue was first prepared in 1876 by Heinrich Caro. It is on the World Health Organization's List of Essential Medicines, the most effective and safe medicines needed in a health system. In the United States a 50 mg vial costs about 191.40 USD. In the United Kingdom a 50 mg vial costs the NHS about 39.38 pounds.
While many texts indicate that methylene blue has oxidizing agent properties, its effects as an oxidizing agent occur only at very high doses. At pharmacologic doses it has reducing agent properties. It is owing to this reason that methylene blue is employed as a medication for the treatment of methemoglobinemia. This can arise from ingestion of certain pharmaceuticals, toxins, or broad beans. Normally, through the NADH or NADPH dependent methemoglobin reductase enzymes, methemoglobin is reduced back to hemoglobin. When large amounts of methemoglobin occur secondary to toxins, methemoglobin reductases are overwhelmed. Methylene blue, when injected intravenously as an antidote, is itself first reduced to leucomethylene blue, which then reduces the heme group from methemoglobin to hemoglobin. Methylene blue can reduce the half life of methemoglobin from hours to minutes. At high doses, however, methylene blue actually induces methemoglobinemia, reversing this pathway.
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