Ferric Carboxymaltose-mediated Methemoglobinemia

Methemoglobinemia is a life-threatening disorder, with levels above 1 percent considered abnormal and typically resulting from drug or toxic substance exposure.

In this study, we describe a case of a 43-year-old woman with a long-standing complaint of fatigue. Iron deficiency anemia was diagnosed based on the blood test findings of hemoglobin of 101 g/L, mean red blood cell volume of 75 fL, ferritin of 2.81 ug/L, transferrin saturation of 4.3 percent, and C-reactive protein of 0.6 mg/L. As a preferred treatment option, 1000 mg ferric carboxymaltose on two distinct days was preferred. After administering the first dose of the medication, we noticed incidentally that methemoglobin levels increased to 2.3%. When venous blood gas was repeated before and after administration of the second dose of the drug, methemoglobin levels were found to be 0.8% and 1.8%, respectively. There was no change in vital signs in both two dosages, and she only suffered a temporary sore throat. Her anemia improved with intravenous iron therapy, and she is currently being followed in our clinic.

No case or research reporting an increase in methemoglobin levels following oral and/or intravenous treatment to patients with iron deficiency anemia has been found in the literature. Therefore, this is the first contribution to the existing literature.