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Health Benefits and Risks of Methylene Blue in Medicine

Linda Crampton is a writer and former teacher with a first-class honors degree in biology. She writes about the scientific basis of disease.

Reflections in a flask of methylene blue

Reflections in a flask of methylene blue

What Is Methylene Blue?

Methylene blue is a dark green powder with important medical and biological uses. When it’s dissolved in water, it forms a beautiful blue solution. It's a popular stain in biology labs because it makes the nucleus of a cell visible. It's also used as a dye in medical tests and during surgery because it colors body fluids and tissues, making them easy to see.

Methylene blue is a medicine as well as a dye. It was the first synthetic drug to be created and was originally used as a malaria treatment. Today it's used to treat a blood disorder called methemoglobinemia and neural problems that may result from treatment by ifosfamide, a chemotherapy drug. In addition, it’s a weak antiseptic and helps to treat urinary tract infections. Research suggests that methylene blue may also be a useful medication for other health problems. In some situations it can be harmful, however.

This is methylene blue powder. On the right, the green powder has dissolved in water drops and become a blue solution.

This is methylene blue powder. On the right, the green powder has dissolved in water drops and become a blue solution.

A Biological Stain

Methylene blue powder is green in color. It actually exists as methylene blue chloride (or more technically, methylthioninium chloride). When this compound is added to water, it breaks up into the positive methylene blue ion, which has a blue color, and the negative chloride ion, which is colorless.

The positive methylene blue ions are attracted to negative particles, such as the nucleic acids (DNA and RNA) in the nuclei of cells. They bind to the nucleic acids and stain them blue, making them more visible than their background.

A Medical Dye

Methylene blue solutions range from light blue to dark blue in color, depending on their concentration. Concentration is an important topic when considering the chemical, not only with respect to its ability to act as a biological stain but also with respect to its safety as a medicine.

Methylene blue's ability to color parts of cells is helpful in certain medical tests. The dye gives doctors an improved view of body tissues. Fortunately, doctors are generally aware of the fact that when the chemical is placed in the body as a dye it might have other effects in certain situations.

New methylene blue and methyl blue are also biological stains. They are not the same chemical as methylene blue, despite their similar names.

Methemoglobinemia Facts

Methylene blue treats health problems as well as acting as a dye. For example, it's very useful for clearing excess methemoglobin from a person's bloodstream. Methemoglobin is a chemically altered form of hemoglobin, the red pigment in our blood that transports oxygen from the lungs to our cells. An excessive amount of methemoglobin in the blood has serious consequences. Unlike normal hemoglobin, the altered form can't transport oxygen effectively. Our cells can't survive without the oxygen supplied by hemoglobin.

Methemoglobinemia is a potentially dangerous disorder in which the blood contains a higher amount of methemoglobin than normal. The condition may be inherited, but it's more often acquired during life. Taking certain medications and eating too many foods containing nitrates or nitrites can cause the disorder. In mild cases of methemoglobinemia, the body can heal itself if the trigger for the disorder is avoided. In more serious cases, medical help is needed.

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Benzocaine in Teething Gel and Methemoglobinemia

One possible cause of acquired methemoglobinemia is giving a baby a teething gel containing benzocaine. Benzocaine is a local anesthetic that relieves gum and mouth pain. The benzocaine may trigger excess methemoglobin production. As the methemoglobin builds up in a baby's blood, the blood may turn brown and the skin, lips, and nail beds may become pale, grey, or blue (cyanosis). Additional symptoms may included shortness of breath and a rapid heartbeat. The condition is a medical emergency.

In May, 2018, the FDA (Food and Drug Administration) warned the public to stop buying teething products containing benzocaine due to the possibility of methemoglobinemia development. It also sent messages to the makers of the teething products to ask them to stop selling them. The FDA said that if the companies didn’t comply, the agency would take regulatory action. The agency says that in addition to being potentially dangerous, the teething products aren't very effective because they are quickly washed away by saliva.

A dilute solution of methylene blue is generally administered intravenously to a patient with methemoglobinemia. This decreases the amount of methemoglobin in the blood. It's important to get the patient to a hospital quickly so that they can receive the treatment.

According to the FDA, methemoglobinemia most often occurs in children younger than two years of age. It may occasionally affect people of other ages, including adults. Adults may report that they have a headache and feel light-headed in addition to having other symptoms.

Ifosfamide Neurotoxicity

Ifosfamide is a very helpful chemotherapy drug for a variety of cancer types. Unfortunately, like other powerful drugs it can cause side effects. Doctors can help to minimize or eliminate any side effects that develop.