Episode 24- An expert talks: methemoglobinemia
Episode Summary:
This week we discuss methemoglobinemia with Dr. KC Lee, a clinical pharmacist who recently completed her clinical toxicology/ emergency medicine fellowship.
Show Notes:
Key Points:
“An expert talks: methemoglobinemia”:
– Methemoglobinemia (MetHgb) occurs when the ferrous heme in hemoglobin (Hgb) becomes oxidized to ferric heme. Ferric hemes do not bind oxygen, and the remaining ferrous hemes bind oxygen more tightly
– MetHgb can be caused by hereditary conditions as well as numerous compounds such as local anesthetics (benzocaine, lidocaine), dapsone, phenazopyridine, and various nitrates and nitrites
– MetHgb levels of <10% can usually be asymptomatic; 10-30% cause cyanosis; 30-50% cause dizziness, fatigue, headache, dyspnea; 50% -70% cause stupor, lethargy, seizures, coma; levels > 70% can be fatal
– Methylene blue is the treatment of choice. It is indicated for patients with MetHgb levels > 20%, or those with lower levels who are compromised
– The dose is 1-2 mg/kg given slowly over 5 minutes followed by a flush. This dose can be repeated 2-3 times if needed. It has a rapid onset (1-2 mins) with a maximum effect at 30 mins
– Caution use in patients on multiple serotonergic agents or those with G6PD deficiency
References:
Price DP, Howland MA. Methemoglobin inducers and methylene blue. Goldfrank’s Toxicologic Emergencies 9th edition: 1698-1710. McGraw-Hill; New York: 2011
Methemoglobin. Hennepin Regional Poison Center Treatment Guidelines. Minnesota Poison Control System. Accessed 9/22/2020