Methylene blue, or methylthioninium chloride, is a chemical compound used as both a dye and a medication. It was first synthesized in 1876 by Heinrich Caro and is listed on the World Health Organization’s List of Essential Medicines.
🧪 Uses
Its primary medical use is to treat methemoglobinemia, a condition where hemoglobin can’t carry oxygen effectively. In severe cases, methylene blue is given by intravenous injection. It is reduced in the body to leucomethylene blue, which helps convert methemoglobin back into functional hemoglobin. It is typically used when methemoglobin levels exceed 30% or when symptoms persist despite oxygen therapy.
Other uses
Redox indicator
Methylene blue is widely used as a redox indicator in analytical chemistry. Solutions of this substance are blue when in an oxidizing environment, but will turn colorless if exposed to a reducing agent.
Photosensitizer
Methylene blue is also a photosensitizer used to create singlet oxygen when exposed to both oxygen and light. It is used in this regard to make organic peroxides by a Diels-Alder reaction which is spin forbidden with normal atmospheric triplet oxygen.
With the help of light, methylene blue can be used to kill some viruses and some bacteria. This kind of photo-disinfection has also been done inside of human bodies (antimicrobial photodynamic therapy). The same process can also be used to disinfect blood plasma.
Methylene blue is theoretically also applicable to other forms of photodynamic therapy, i.e., the use of oxygen, light, and a photosensitizer to kill cells. Research on using it to kill cancer cells locally is in a preclinical stage.
