Methemoglobinemia Causes and Associated Conditions

Introduction to Methemoglobinemia

Methemoglobinemia results from either acquired exposures to oxidizing substances or inherited genetic defects affecting hemoglobin reduction pathways, with acquired causes being more frequent than congenital forms 1, 2

Local anesthetics, such as benzocaine and lidocaine, can cause methemoglobinemia 3
Antimalarials, including chloroquine and primaquine, are associated with methemoglobinemia 3
Antibiotics like sulfonamides and trimethoprim can induce methemoglobinemia 3
Other agents, including phenacetin, metoclopramide, and cyclophosphamide, can also cause methemoglobinemia 3
Contaminated well water or food with excessive nitrates can lead to methemoglobinemia, particularly in infants and pregnant women 3

Biallelic mutations in the CYB5R3 gene cause NADH cytochrome b5 reductase deficiency, resulting in methemoglobinemia, with over 80 different disease-causing variants reported 4, 5
Type I cytochrome b5 reductase deficiency typically presents with MetHb levels above 25%, causing cyanosis, headache, fatigue, and dyspnea 4, 5
Hemoglobin M disease, caused by autosomal dominant variants in globin genes, leads to structural hemoglobin abnormalities and methemoglobinemia, with MetHb levels typically ranging 12.5%-25% 1, 4, 5, 6, 7

Elevated MetHb can occur secondarily in patients with unstable hemoglobins and G6PD deficiency, particularly after exposure to oxidant drugs 6, 7
Infants are at substantially greater risk of methemoglobinemia due to lower erythrocyte CYB5R activity, making them more susceptible to both acquired and congenital forms 7

Oxidant stressors convert ferrous iron (Fe²⁺) to ferric iron (Fe³⁺) in hemoglobin, impairing oxygen transport and leading to acquired methemoglobinemia【8】.
Certain pharmaceuticals are documented triggers of acquired methemoglobinemia, including phenazopyridine, metoclopramide, phenacetin, and cyclophosphamide【8】.

Biallelic mutations in the CYB5R3 gene cause NADH cytochrome b5 reductase deficiency, an autosomal‑recessive disorder that predisposes individuals to elevated methemoglobin levels【9】.
Autosomal‑dominant variants in globin genes produce hemoglobin M disease, a structural hemoglobin abnormality that results in chronically increased methemoglobin concentrations【9】.

Patients with glucose‑6‑phosphate dehydrogenase (G6PD) deficiency are at heightened risk for secondary methemoglobinemia when exposed to oxidizing medications【8】.