Methylene blue

Regarding methylene blue, the following statements are true EXCEPT which one?

a) It has been used in cases of anaphylaxis previously unresponsive to standard

treatment

b) It has been used in combination with light to treat psoriasis

c) It has been used to treat arsenic poisoning

d) It has been used to treat methaemoglobinaemia

e) It has been used to treat malaria

Answer: c

Explanation

Methylene blue has had many uses in medicine. It has been used successfully in the

treatment of anaphylaxis resistant to all other therapies, with light in the treatment of

psoriasis, in managing methaemoglobinaemia and treating malaria. Its main historical

indication in the management of poisons was to treat potassium cyanide toxicity.

Cyanide inhibits mitochondrial cytochrome oxidase, causing cytotoxic hypoxia.

Methylene blue is not now recommended as it may reverse treatment with nitrites,

releasing free cyanide. It is not used in the treatment of arsenic poisoning. Methylene

blue sometimes contains small quantities of arsenic as an impurity. This has been put

forward as an explanation for the gastrointestinal symptoms some patients experience

when treated with methylene blue.