Methylene blue

Methylthioninium chloride, commonly called methylene blue.

Methylene blue is a medication and dye that has various uses in medicine and research.

Methylene blue can be used for a variety of medical purposes, including:

Treatment of methemoglobinemia

Urinary tract infections: it helps to reduce bacteria growth.

Antiseptic properties that can be applied topically to treat certain skin infections.

Methylene blue is commonly used as a histological stain in medical laboratories to facilitate the examination of tissues under a microscope.

It has been studied for its potential therapeutic effects in a range of conditions: neurodegenerative disorders, such as Alzheimer’s disease and Parkinson’s disease, and for certain psychiatric disorders and some types of cancer.

It is a salt used as a dye and as a medication. 

Pregnancy category AU: D

Routes of administration By mouth, intravenous

Elimination half-life 5 to 24 hours

As a medication, it is mainly used to treat methemoglobinemia by converting/chemically reducing the ferric iron in hemoglobin to ferrous iron.

It is used to treat methemoglobin levels that are greater than 30% or in which there are symptoms despite oxygen therapy.

Methylene blue is typically given intravenously.

Common side effects include headache, vomiting, confusion, shortness of breath,  high blood pressure, blue or green discoloration of urine, sweating, dizziness,, and rare allergic reactions.

Other side effects include: serotonin syndrome, red blood cell breakdown, and allergic reactions.

Its use often turns the urine, sweat, and stool blue to green in color.

While use during pregnancy may harm the baby, not using it in methemoglobinemia is likely more dangerous.

Methylene blue is employed as a medication for the treatment of methemoglobinemia, which can arise from ingestion of certain pharmaceuticals, toxins, or broad beans.

Through the NADH or NADPH dependent methemoglobin reductase enzymes, methemoglobin is reduced back to hemoglobin, but 

When large amounts of methemoglobin occur secondary to toxins, methemoglobin reductases are overwhelmed. 

Methylene blue, when injected intravenously is 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.

Large doses of methylene blue are sometimes used as an antidote to potassium cyanide poisoning.

Methylene blue is used in endoscopic polypectomy as an addition to saline or epinephrine.

It is used for injection into the submucosa around the polyp to be removed.allowing the submucosal tissue plane to be identified after the polyp is removed.

It is useful in determining if more tissue needs to be removed, or if there has been a high risk for perforation. 

Methylene blue can also used in chromoendoscopy, as it can be sprayed onto the mucosa of the gastrointestinal tract to identify dysplasia, or pre-cancerous lesions. 

Intravenously methylene blue can be used to test the urinary tract for leaks or fistulas.

In sentinel lymph node dissections, methylene blue can be used to visually trace the lymphatic drainage of tested tissues. 

Methylene blue is added to bone cement in orthopedic operations to provide easy discrimination between native bone and cement. 

Methylene blue accelerates the hardening of bone cement.

Methylene blue is used as an aid to visualisation/orientation in a number of medical devices, in fistulas and pilonidal sinuses to identify the tract for complete excision, and can also be used during gastrointestinal surgeries to test for leaks.

In cytopathology It confers a blue color to both nuclei and cytoplasm, and makes the nuclei more visible.

The  application of methylene blue is up in the intravital or supravital staining of nerve fibers.

Methylene blue is a dye that is commonly used in the food industry to test the purity of milk.

When added to a sample of milk it should remain blue, otherwise the sample is impure or contaminated.

Methylene blue is to treat ifosfamide neurotoxicity.

Methylene blue consistently increases blood pressure in people with redistributive shock, but has not been shown to improve delivery of oxygen to tissues or to decrease mortality.

Methylene blue has been used in calcium channel blocker toxicity as a rescue therapy for distributive shock unresponsive to first line agents. 

Side effects


Precordial pain


Mental confusion



Staining of skin

Injection site necrosis (SC)

Fecal discoloration



Abdominal pain

Discoloration of urine (doses over 80 µg)

Bladder irritation


Methylene blue is a monoamine oxidase inhibitor (MAOI), and if infused intravenously at doses exceeding 5 mg/kg, may precipitate serious serotonin toxicity, serotonin syndrome if combined with any selective serotonin reuptake inhibitors (SSRIs) or other serotonin reuptake inhibitor (e.g., duloxetine, sibutramine, venlafaxine, clomipramine, imipramine).

It causes hemolytic anemia in carriers of the G6PD (favism) enzymatic deficiency.

It is widely used as a redox indicator in analytical chemistry.

Methylene blue  is blue when in an oxidizing environment, but will turn colorless if exposed to a reducing agent. 

It has industrial use as a perroxide generator, a photosensitizer, for sulfide analysis, water testing, distinguishes between surfactants.

Methylene blue is used for different staining procedures, such as Wright’s stain and Jenner’s stain. 

It can also be used to examine RNA or DNA under the microscope or in a gel.

It can also be used as an indicator to determine whether eukaryotic cells such as yeast are alive or dead:  dead cells are unable to reduce the oxidized methylene blue and the cells are stained blue. 

Methylene blue is used in aquaculture and by tropical fish hobbyists as a treatment for fungal infections. 

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