This can result in significant cyanosis, despite nontoxic levels of methemoglobin. Clinical signs and symptoms of methemoglobinemia result from the inability to transport oxygen and carbon dioxide. Also dizziness, fatigue, headache, tachycardia, and weakness may occur. Hemolysis and anemia often occur 4-5 days after the ingestion. The management of dapsone is initially directed at gastric lavage and gastrointestinal decontamination.
Dapsone has a long elimination half-life and undergoes enterohepatic recirculation.
Methemoglobinemia should be considered when there is little improvement in cyanosis or dyspnea when oxygen is administered to a patient known to have taken dapsone. Also laboratory monitoring should include arterial blood gas measurements, methemoglobin levels, a complete blood count, and a reticulocyte count. Most methemoglobin should be converted to hemoglobin within 1 hour, though a second dose should be given 2-4 hours later if cyanosis or hypoxia persists. In large doses there are adverse effects associated with methylene blue, such as nausea, vomiting, diarrhea, restlessness, and sweating. Individuals poisoned with dapsone but unresponsive to methylene blue may require blood transfusions.