Introduction:
Methemoglobinemia is considered a rare and serious disorder of the blood and if left untreated can be fatal. Methemoglobinemia is defined as an increase in methemoglobin levels in the blood. The underlying mechanism includes changing the hemoglobin heme iron from a ferrous to a ferric state and eventually may lead to decrease oxygen delivery to the tissues. Methemoglobinemia can be congenital or acquired due to toxins or drugs. There are few reports of methemoglobinemia induced by traditional dosing of SMX/TMP. However, in our case, methemoglobinemia occurred within three days from the initiation of a high dose of SMX/TMP with a rapid resolution of methemoglobinemia after discontinuation of SMX/TMP.