The presence of methaemoglobin in the blood.
A condition due to the presence in the blood of methaemoglobin. It is characterized by cyanosis which turns the skin and lips a blue colour, shortness of breath, headache, fatigue and sickness. There are two main forms: a hereditary form and a toxic form. The latter can be caused by certain drugs, including acetanilide, phenacetin, the sulphonamides and benzocaine. The treatment of the toxic form is the withdrawal of the causative drug. In the more severe cases the administration of methylene blue or ascorbic acid may also be needed; these are the drugs used in the hereditary form.