Medical Author: Melissa Conrad Stöppler, MD
Methemoglobinemia is a condition in which more than 1% of the hemoglobin in red blood cells takes the form of methemoglobin. Methemoglobulin is an abnormal form of hemoglobin (the molecule responsible for carrying oxygen in the blood cells) that is unable to bind to oxygen. A small amount of methemoglobin is normal (less than 1% of hemoglobin). Symptoms of anemia develop when this percentage increases over 10%, and levels of 70% are generally fatal.
Methemoglobin can be increased due to two main causes. Some cases of methemoglobinemia are genetic, meaning that an inborn metabolic error leads to an increased proportion of methemoglobin. Most cases of methemoglobinemia are, however, acquired rather than inborn. Exposure to certain oxidizing substances may lead to the conversion of hemoglobin to methemoglobin. Known toxins that can cause methemoglobinemia include aniline dyes, nitrates or nitrites, and, importantly, many medications. The most common medications that have been linked to acquired methemoglobinemia are local anesthetics (lidocaine, prilocaine, and benzocaine) and dapsone, an agent that has been used for the treatment and prevention of Pneumocystis jiroveci (PCP) infection.
Medically Reviewed by a Doctor on 12/9/2014