Methemoglobinemia

Question 1

Pathophysiology

Answer 1

Altered state of hemoglobin in which the heme iron is oxidized from the ferrous (Fe2+) to the ferric (Fe3+) state. The ferric hemes of methemoglobin do not bind O2. The ferric heme in the hemoglobin tetramer also causes the remaining normal ferrous hemes within the same tetrameric hemoglobin molecule to have increased O2 affinity [1]. This produces a left shift of the hemoglobin oxygen dissociation curve and in turn further decreases O2 delivery to the tissues.

Question 2

Most commonly implicated meds

Answer 2

• Dapsone and topical anesthetic agents (eg, benzocaine, lidocaine, prilocaine) [48,51,58-60], hydroxychloroquine, benzocaine spray (VA pulled it from formulary). - Drugs (These agents are commonly added to heroin, cocaine, and other “street drugs”).

Question 3

Management

Answer 3

Eliminate exposure
ICU transfer
Supportive care for hypoxemia
IF no G6PD history AND not on serotonergic medication → methylene blue