Which local anesthetic is associated with methemoglobinemia?

Which local anesthetic is associated with methemoglobinemia?

• A. Lidocaine
• B. Prilocaine
• C. Chloroprocaine
• D. Bupivacaine

Answer: (B)

Methemoglobinemia happens when an oxidizing metabolite from a local anesthetic converts iron in hemoglobin from the ferrous (Fe2+) to the ferric (Fe3+) state, so hemoglobin can’t carry oxygen effectively. Prilocaine is classically associated with this issue because its metabolite, o-toluidine, is a potent oxidizer of hemoglobin. This risk rises with higher doses or in susceptible patients (such as neonates or those with certain enzyme deficiencies). Clinically, this presents as cyanosis that doesn’t improve with oxygen and can be accompanied by headache, tachycardia, or dyspnea; blood may appear chocolate-colored. If methemoglobinemia occurs, the offending agent should be avoided and treatment started promptly with methylene blue IV (unless contraindicated by G6PD deficiency). Other local anesthetics listed are not the typical culprits for this complication.

Methemoglobinemia happens when an oxidizing metabolite from a local anesthetic converts iron in hemoglobin from the ferrous (Fe2+) to the ferric (Fe3+) state, so hemoglobin can’t carry oxygen effectively. Prilocaine is classically associated with this issue because its metabolite, o-toluidine, is a potent oxidizer of hemoglobin. This risk rises with higher doses or in susceptible patients (such as neonates or those with certain enzyme deficiencies). Clinically, this presents as cyanosis that doesn’t improve with oxygen and can be accompanied by headache, tachycardia, or dyspnea; blood may appear chocolate-colored. If methemoglobinemia occurs, the offending agent should be avoided and treatment started promptly with methylene blue IV (unless contraindicated by G6PD deficiency). Other local anesthetics listed are not the typical culprits for this complication.