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Introduction: Methemoglobinemia can be either acquired or inherited. Most of the cases in the literature are acquired and associated with drugs especially dapsone and benzocaine. The prompt recognition of this condition is imperative in patient treatment and recovery. Symptoms can be indolent or develop within hours and treatment consist of methylene blue intravenous.

Case presentation: Patient is a 59-year-old woman with hypertension and recent shoulder surgery was found down at home. According to her husband, she was feeling lightheadedness and diaphoresis for the past 3 days before her admission with a dry cough but no fevers or chills. At her presentation, patient cyanotic and oxygen saturation at 75% not increased with 100% oxygen. The husband referred that patient uses vaginal benzocaine for itching. At the emergency department, her initial labs did not show abnormalities, chest x-ray was normal. Arterial blood gas was performed showing 35% of methemoglobin. Prompt treatment with methylene blue was initiated and patient did recover within hours. She was discharged home asymptomatic.

Discussion: Acquired methemoglobinemia is a rare condition but commonly associated with topic anesthetics like benzocaine. This medication is an over the counter formulation and can be easily found in groceries. The differential diagnosis is broad and clinicians should be suspicious of this condition whenever they find a combination of cyanosis not reverted with 100% oxygen and exposure to drugs such as dapsone or benzocaine. Treatment with methylene blue is the first choice and should be initiated as soon as possible.

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