Methemoglobinemia is a condition where Fe+2 form of iron in hemoglobin is converted to Fe+3 form, resulting in inability to release oxygen in the blood. The resultant is tissues deprived of oxygen despite the normal oxygen saturation.
The causes of methemoglobinemia may be congenital or acquired. The congenital methemoglobinemia is associated with enzyme deficiency secondary to gene defects. The acquired etiology of methemoglobinemia is exposure to certain drugs and water contaminated with nitrates.
Benzocaine, a local anesthetic drug, dapsone, and nitrous oxide are particularly associated with methemoglobinemia.
Methemoglobinemia may be a medical emergency. It is treated by infusion of methylene blue. Usually acquired methemoglobinemia is responsive to methylene blue. The congenital form of methemoglobinemia usually require blood transfusion.
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