Sections View Full Chapter Figures Tables Videos Annotate Full Chapter Figures Tables Videos Supplementary Content + Download Section PDF Listen ++ For further information, see CMDT Part 38-45: Methemoglobinemia-Inducing Agents Poisoning + Key Features Download Section PDF Listen +++ ++ Oxidation of hemoglobin to methemoglobin can be caused by Benzocaine Aniline Propanil Nitrites Nitrogen oxide gases Nitrobenzene Dapsone Phenazopyridine Many other oxidants Dapsone has a long half-life and may produce prolonged or recurrent methemoglobinemia Amyl nitrite and isobutyl nitrite ("poppers") are inhaled as sexual stimulants but can result in methemoglobinemia + Clinical Findings Download Section PDF Listen +++ ++ Severity of symptoms depends on the percentage of hemoglobin oxidized to methemoglobin Severe poisoning is usually present when methemoglobin fractions are > 40–50% Even at low levels (15–20%), victims appear cyanotic because of the chocolate-brown color of methemoglobin Dizziness Nausea Headache Dyspnea Confusion Seizures Coma + Diagnosis Download Section PDF Listen +++ ++ PO2 results are normal on arterial blood gas determinations; conventional pulse oximetry gives inaccurate oxygen saturation measurements Severe metabolic acidosis Hemolysis may occur, especially in patients with glucose-6-phosphate dehydrogenase deficiency + Treatment Download Section PDF Listen +++ ++ Administer high-flow oxygen Activated charcoal Administer 60–100 g orally or via gastric tube, mixed in aqueous slurry for ingestions within 1 h Repeat-dose may enhance dapsone elimination For symptomatic patients, administer methylene blue, 1–2 mg/kg (0.1–0.2 mL/kg of 1% solution) intravenously The dose may be repeated once in 15–20 min if necessary Patients with hereditary methemoglobin reductase deficiency or glucose-6-phosphate dehydrogenase deficiency may not respond to methylene blue In severe cases where methylene blue is not available or is not effective, exchange blood transfusion may be necessary