Methemoglobinemia in Emergency Medicine Medication
- Author: David C Lee, MD; Chief Editor: Asim Tarabar, MD more...
Medication Summary
Methylene blue is the first-line antidotal therapy.
Methylene blue accelerates the enzymatic reduction of methemoglobin by NADPH-methemoglobin reductase and also reduces to leucomethylene blue that, in turn, reduces methemoglobin. The initial dose is 1-2 mg/kg IV over 5 min. Its effects should be seen in approximately 20 min to 1 h. Patients who are exposed may require repeated dosing, but high doses of methylene blue may actually induce a paradoxical methemoglobinemia.
Treatment failure may occur in patients with ongoing exposure, patients exposed to sulfhemoglobinemia, and patients who have deficient NADPH-methemoglobin reductase enzymatic pathways. Methylene blue should be avoided in patients with G-6-PD deficiency, if possible, because case reports and in vitro models suggest that this antidote may induce hemolysis in this patient population. G-6-PD deficiency should be considered in patients who fail to respond to methylene blue.
Cimetidine can be used in dapsone-induced methemoglobinemia to prevent further formation of its metabolite who is also responsive as an oxidizing agent.
Hyperbaric oxygen and exchange transfusion should be considered for patients who are not candidates for methylene blue treatment or when methylene blue is ineffective.
Pharmacologic antidotes
Class Summary
Are used to pharmacologically counteract the condition. Cimetidine may be used in dapsone-induced methemoglobinemia.
Methylene blue (Urolene blue)
Effective treatment for methemoglobinemia. Most patients require only 1 dose. Resolution of toxicity should be seen within 1 h, often within 20 min.
Available as 1% solution (10 mg/mL).
The FDA warns against the concurrent use of methylene blue with serotonergic psychiatric drugs, unless indicated for life-threatening or urgent conditions. Methylene blue may increase serotonin CNS levels as a result of MAO-A inhibition, increasing the risk of serotonin syndrome.[3]
Cytochrome P-450 inhibitors
Class Summary
Recommended only for patients with methemoglobinemia secondary to dapsone.
Cimetidine (Tagamet)
Inhibits conversion of dapsone to its oxidizing metabolite, dapsone hydroxylamine, by the P-450 system. Thus, cimetidine prevents further development of methemoglobinemia in this select patient population.
Moore TJ, Walsh CS, Cohen MR. Reported adverse event cases of methemoglobinemia associated with benzocaine products. Arch Intern Med. Jun 14 2004;164(11):1192-6. [Medline].
Ash-Bernal R, Wise R, Wright SM. Acquired methemoglobinemia: a retrospective series of 138 cases at 2 teaching hospitals. Medicine (Baltimore). Sep 2004;83(5):265-73. [Medline].
US Food and Drug Administration. FDA Drug Safety Communication: Serious CNS reactions possible when methylene blue is given to patients taking certain psychiatric medications. Available at http://www.fda.gov/Drugs/DrugSafety/ucm263190.htm. Accessed July 27, 2011.
Conkling PR. Brown blood: understanding methemoglobinemia. N C Med J. Mar 1986;47(3):109-11. [Medline].
Ellenhorn MJ, Barceloux DG. Nitrates, nitrites, and methemoglobinemia. In: Medical Toxicology, Diagnosis and Treatment of Human Poisonings. 1988:844-851.
Fitzsimons MG, Gaudette RR, Hurford WE. Critical rebound methemoglobinemia after methylene blue treatment: case report. Pharmacotherapy. Apr 2004;24(4):538-40. [Medline].
Henretig FM, Gribetz B, Kearney T, Lacouture P, Lovejoy FH. Interpretation of color change in blood with varying degree of methemoglobinemia. J Toxicol Clin Toxicol. 1988;26(5-6):293-301. [Medline].
Herman MI, Chyka PA, Butler AY, Rieger SE. Methylene blue by intraosseous infusion for methemoglobinemia. Ann Emerg Med. Jan 1999;33(1):111-3. [Medline].
Howland MA. Methylene blue. In: Goldfrank's Toxicologic Emergencies. 8th ed. 2006:1746-1748.
Price D. Methemoglobin inducers. In: Goldfrank's Toxicologic Emergencies. 8th ed. 2006:1734-1745.
Umbreit J. Methemoglobin--it's not just blue: a concise review. Am J Hematol. Feb 2007;82(2):134-44. [Medline].
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