Algorithm for managing acquired/toxic methemoglobinemia
Algorithm for managing acquired/toxic methemoglobinemia
All individuals should be evaluated for other possible causes of their symptoms and other possible toxic exposures. Individuals with congenital methemoglobinemia as well as CYB5R3 heterozygotes are likely to have increased susceptibility to acquired/toxic methemoglobinemia. For individuals with severe methemoglobinemia who require treatment, MB is preferred (when not contraindicated) due to its rapid and complete reversal of methemoglobinemia. MB can cause severe hemolysis in individuals with G6PD deficiency or life-threatening serotonin syndrome in individuals taking an SSRI or other serotonergic agent; ascorbic acid is used in these cases. Refer to UpToDate for additional details of our approach to management.
G6PD: glucose-6-phosphate dehydrogenase; MB: methylene blue; CYB5R3: cytochrome b5 reductase gene; SSRI: selective serotonin reuptake inhibitor. * Symptoms attributable to methemoglobinemia may be nonspecific (headache, lethargy, irritability); with higher levels, cyanosis, respiratory failure, neurologic changes (seizures, coma) may occur. ¶ Ascorbic acid dose: 1.5 to 2 grams intravenously. Some individuals for whom G6PD status is unknown may be treated cautiously with MB instead. Δ Methylene blue dose: 1 to 2 mg/kg intravenously. ◊ Improvement is assessed clinically; the tempo of monitoring depends on the severity of disease. Routine laboratory monitoring is not used because MB interferes with methemoglobin measurements.
