What is methylene blue?

Methylene blue, also known as methylthioninium chloride, is a synthetic compound with a wide range of uses in medicine, science, and industry.

Chemical Properties and History

• Methylene blue is a salt with the chemical formula C₁₆H₁₈ClN₃S and a molar mass of 319.85 g/mol.

• It was first synthesized in 1876 by Heinrich Caro and is considered the first fully synthetic drug used in medicine.

• The compound appears as a dark green powder that produces a blue solution in water.

Medical Uses

Primary Use:

• Methylene blue is FDA-approved and primarily used to treat methemoglobinemia, a rare blood disorder where hemoglobin cannot effectively release oxygen to body tissues.

• It works by chemically reducing methemoglobin (ferric iron) back to hemoglobin (ferrous iron), restoring the blood’s oxygen-carrying capacity.

Other Medical Applications:

• Historically, it has been used as an antidote for cyanide poisoning, though this is now less common.

• It has also been used in the treatment of malaria, and it served as a prototype for the development of other antimalarial drugs.

• Methylene blue is sometimes used off-label for identifying abnormal cells during diagnostic procedures, such as highlighting cancerous tissue, and for certain types of fungal infections in combination with light therapy.

• It is administered intravenously or orally, and common side effects include headache, nausea, and vomiting.

Laboratory and Research Uses

• Methylene blue is widely used as a biological stain in microscopy to visualize cells, nucleic acids (DNA/RNA), andi bacteria.

• It can distinguish between living and dead cells, as viable cells reduce the dye and remain unstained, while dead cells retain the blue color.

Industrial and Other Uses

• In aquaculture, methylene blue is used to treat fungal infections in fish and protect fish eggs from fungal contamination.

• It is also used as a chemical intermediate in the synthesis of dyes, pigments, and pharmaceuticals.