Idiosyncratic Reactions

Methemoglobinemia is an uncommon idiosyncratic reaction most notably to prilocaine and topical benzocaine.21‑25,28,29,58‑62 Their metabolites bind to hemoglobin and interfere with its oxygen-carrying capacity. Signs and symptoms usually appear 3 to 4 hours after exposure to large doses and may include cyanosis, fatigue, weakness, nausea, sedation, seizures, and coma. Very young patients and those with congenital methemoglobinemia or glucose-6-phosphate deficiency are the most susceptible.