Methemoglobinemia Associated With Topical Anesthetics

Abstract and Introduction

Abstract

Background: Topical anesthetics are commonly used over the counter, and one of the adverse effects of these medications is methemoglobinemia, which is a serious and life-threatening condition.

Case Presentation: We describe a 25-year-old Persian male presenting with generalized weakness, dizziness, headache, and cyanosis. In addition, he had genital warts starting 3 weeks ago, which were self-treated with podophyllin, resulting in itching and pain. He used over-the-counter topical anesthetics, including benzocaine and lidocaine, to reduce the symptoms. According to the lab data, signs and symptoms of methemoglobinemia and hemolysis were diagnosed. Considering the hemolysis, ascorbic acid was used for treatment. The patient was discharged after 5 days with normal arterial blood gas and pulse oximetry and no signs and symptoms.

Conclusion: This case highlights that self-administration of some topical anesthetics may lead to potentially fatal conditions.

Introduction

Hemoglobin A (Hb), the main type of the hemoglobin in adolescents, contains ferrous iron (Fe²⁺) and four heme groups.^[1] Oxidization of the ferrous iron (Fe²⁺) to ferric iron (Fe³⁺) produces methemoglobin.^[1] Methemoglobin is incapable of binding, transporting, and releasing oxygen into the tissues effectively, resulting in hypoxia and functional anemia.^[2] Physiological mechanisms and enzymatic systems protect the red blood cells against oxidative stress and try not to let the methemoglobin levels exceed 1–2% of the total haemoglobin.^[2,3] Methemoglobinemia, which means high levels of methemoglobin in the blood, is a rare but life-threatening condition, presenting in hereditary or acquired forms.^[4] Hemoglobin M disease, cytochrome b₅ reductase deficiency, and glucose-6-phosphate dehydrogenase (G6PD) deficiency are causes of hereditary methemoglobinemia.^[5] Furthermore, some drugs, such as dapson, nitroglycerine, nitroprusside, nitric oxide, sulfanamides, phenazopyridine, chloroquine, lidocaine, prilocaine, and benzocaine, may cause acquired methemoglobinemia.^[4,5] Cocaine-derived anesthetics, including lidocaine and benzocaine, are extensively used in medical procedures, such as endoscopy and bronchoscopy;^[6] moreover, they may be used topically.^[6] In this study, we present a unique and atypical case of methemoglobinemia and hemolysis induced by self-administration of topical lidocaine and benzocaine.