Methemoglobinemia: Etiology, pharmacology, and clinical management

Methemoglobin (MHb) may arise from a variety of etiologies including geneti c, dietary, idiopathic, and toxicologic sources. Symptoms vary from mild he adache to coma/death and may not correlate with measured MHb concentrations , Toxin-induced MHb may be complicated by the drug's effect on other organ systems such as the liver or lungs. The existence of underlying heart, lung , or blood disease may exacerbate the toxicity of MHb. The diagnosis may be complicated by the effect of MHb on arterial blood gas and pulse oximeter oxygen saturation results. In addition, other dyshemoglobins may be confuse d with MHb. Treatment with methylene blue can be complicated by the presenc e of underlying enzyme deficiencies, including glucose-6-phosphate dehydrog enase deficiency. Experimental antidotes for MHb may provide alternative tr eatments in the future, but require further study.