Shafiepour,m MD. Kerman university of medical sciences

A patient with human immunodeficiency virus had a rash in association with trimethoprim sulfamethoxazole used as prophylaxis for Pneumocystis carinii pneumonia. An alternative medication was used, but the patient took 3 times the normal dose by mistake. He became dyspneic, and headache, nausea and vomiting, and the skin discoloration shown here developed (a normal hand is shown for contrast on the right).

1. What was the alternative medication? 1a. Pentamidine 1b. Pyrimethamine-sulfonamide 1c. Atovaquone 1d. Dapsone 1e. Clindamycin-primaquine

2. In addition to supplemental oxygen, which one of the following would be the most appropriate antidote? 2a. N-Acetylcysteine 2b. Amyl nitrite 2c. Methylene blue 2d. Deferoxamine 2e. 4-Methylpyrazole

Methemoglobinemia Due to Dapsone Overdose Methemoglobin is the ferric form of hemoglobin (HbFe3+) that cannot bind oxygen Although sometimes inherited, it is more often formed by oxidative stress Among drugs, nitrites are commonly associated with this condition Chocolate-brown or slate-blue cyanosis unrelieved with oxygen suggests the diagnosis

Arterial blood gas studies will show normal arterial oxygen pressure but low oxygen saturation. Pulse oximetry results will be inappropriately increased (the pulse oximeter result will be higher than the actual oxygen saturation, although the absolute value may still be below normal)

Methylene blue is the antidote for patients with severe hypoxia, unless they have glucose-6 phosphate dehydrogenase deficiency, in which case it may worsen the clinical condition. If the patient has this deficiency, ascorbic acid can be used to reduce the methemoglobin

The characteristic muddy appearance of freshly drawn blood can be a critical clue. The best diagnostic test is methemoglobin assay, which is usually available on an emergency basis. Methemoglobinemia often causes symptoms of cerebral ischemia at levels >15%; levels >60% are usually lethal. Intravenous injection of 1 mg/kg of methylene blue is effective emergency therapy. Milder cases and follow-up of severe cases can be treated orally with methylene blue (60 mg three to four times each day) or ascorbic acid (300–600 mg/d).