Maternal use of these agents has been known to cause fetal methemoglobinemia. Symptoms of methemoglobinemia include headaches, fatigue, coma, and death. It remains in the mucous membranes and lips even when the skin has become blue to purple with increasing levels of methemoglobinemia. Blood will continue to remain chocolate to brown colored despite exposure to oxygen. The urine may be brown to black in color due to the presence of methemoglobin.
Treatment involves general supportive care and removal of any offending toxins.
This may include vigorous washing of the skin and clothing, gastric lavage, cathartics, and even hemodialysis. The drug of choice for treating severe methemoglobinemia is methylene blue. This compound can be reduced to leukomethylenne blue. In low concentrations methylene blue and leukomethylene blue form a reversible oxidation reduction system which can enhance erythrocytic reduction of methemoglobin. In high concentrations however, methylene blue can actually cause oxidation of hemoglobin and increase methemoglobin levels.