Cetirizine as a Causative Agent for Drug Induced Methemoglobinemia: A Case Report and Review.

A case of methemoglobinemia (MHb) in a teenage woman, triggered by an acute ingestion of approximately 120 to 180 mg of cetirizine, allegedly, with no suicidal intent is described. The patient presented with anxiety and tremors and rapidly developed central cyanosis unresponsive to oxygen supplementation. There was a history of recurrent, spontaneously remitting, unprovoked "blue discoloration of hands." Investigations confirmed the diagnosis of MHb, and the patient responded to ascorbic acid and methylene blue, although the baseline methemoglobin level remained slightly high. The exact enzymatic deficiency could not be ascertained as the patient refused to undergo complete testing. To the best of our knowledge, this is the first documentation of cetirizine as a causative agent for drug induced MHb. Cetirizine, a selective histamine H1 receptor antagonist is eliminated via oxidation and conjugation processes, which use pathways other than cytochrome P450 enzyme system. The metabolism could potentially create by-products, like superoxide or hydrogen peroxide, which could act as strong reducing agents and oxidize hemoglobin into ferric containing methemoglobin. In this case, an unusually high systemic load of the drug speculatively saturated and overwhelmed the protective enzyme systems, which resulted in clinical manifestation of MHb.