• Large doses of prilocaine, generally greater then 600 mg, can result in methemoglobinemia in selected patients. Intravenous doses of articaine have been reported to cause similar problems. This occurs as a result of one of the metabolites of the drug converting reduced hemoglobin to methemoglobin. The patient will experience cyanosis with dark blood. Pulse oximetry remains normal since the monitor mistakenly interprets methemolgobin as oxyhemoglobin but the actual oxygen carrying capacity is decreased resulting in the cyanosis. Small doses of methylene blue ( 1-2 mg/kg) will convert the methemoglobin back to reduced hemoglobin
  • This condition can be precipitated by nitrates, acetaminophen, prilocaine, articaine, and a number of other medications. The oxidized (ferric) state of methemoglobin cannot be reverse to the ferrous state by increasing FiO2. Cautious administration of methylene blue will reduce methemoglobin back to ferrous state, normalizing the oxygen binding/delivering capacity of hemoglobin.