Methemoglobinemia: life-threatening hazard of multiple drug ingestions.

There is a long list of prescribed and over the counter oxidizing agents that can induce methemoglobinemia. We report a case of methemoglobinemia in a 46-year-old man with a mayor depression disorder who ingested 30 pills of diphenhydramine, 30 pills of haloperidol, 20 pills of dolagesic, 20 pills of cyclobenzaprine, 20 pills of naproxen, 14 pills of cephalexin, and 48 pills of chlorzoxazone. On admission, he was on mechanical ventilation, and responded only to painful stimuli. Five hours later his face, hands and feet became cyanotic. The pulse oximetry revealed a Sp02 of 85%. The dark chocolate color arterial blood showed a Pa02 of 290.8 mm Hg and oxygen saturation (Sa02) of 99%. The chocolate color arterial blood and unchanged Sp02 suggested the diagnosis of methemoglobinemia. One mg per Klg of intravenous methylene blue was administered in 5 minutes. Twenty minutes later, the cyanosis began to fade and one hour later, it had disappeared and the Sp02 was 99%. Early treatment of methemoglobinernia is crucial in preventing tissue hypoxia. Methylene blue is the treatment of choice in symptomatic patients. The initial dose of methylene blue is 1-2 mg/kg of a 1% solution administered over 5 minutes. Reduction of methemoglobin is usually complete within 1 hour. If methemoglobinernia persists, a second dose not to exceed a total dose of 5-7 mg/kg may be administered. Because headache, nausea, vomiting, diarrhea, and angina may occur with therapeutic doses, methylene blue should only be administered to those patients with symptoms or signs of hypoxia.