Methemoglobinemia induced by an over-the-counter medication

To report a case of methemoglobinemia induced by benzocaine and resorcinol (Vagisil) cream, an over-the-counter medication that was used to treat diaper rash in a neonate.

A 6-day-old, 3350-g white boy was found to be cyanotic with blue mucous membranes on presentation. He had a diaper rash that was red and irritated, which his mother had treated with Vagisil cream. Methemoglobinemia secondary to absorption of benzocaine and resorcinol (1,3-benzenediol) from the Vagisil was diagnosed, with a methemoglobin level of 35% on admission (normal 0.4-1.5). Intravenous methylene blue 3 mg (1 mg/kg) was given; the neonate's skin color returned to normal 45 minutes after the dose.

Methemoglobinemia is a condition in which hemoglobin is oxidized to the ferric form. Oxidized hemoglobin, methemoglobin, is incapable of reversibly binding oxygen at the physiologic partial oxygen pressure. Main causes of methemoglobin formation are exposure to certain oxidizing agents and drugs, deficiency of one of the enzymes necessary for reduction of methemoglobin to hemoglobin, or the presence of an abnormal hemoglobin resistant to reduction. Clinical manifestations of methemoglobinemia include diffuse slate-gray cyanosis with low oxygen saturation in the absence of respiratory distress. A single intravenous dose of methylene blue 1-2 mg/kg is the treatment of choice.

Newborn infants are at increased risk for methemoglobinemia due to diminished enzyme systems required to reduce ferrihemoglobin to ferrohemoglobin, as well as because fetal hemoglobin is more easily oxidized than is adult hemoglobin. It is important to recognize possible drug reactions and educate parents on the potential risks of treatment with over-the-counter medications, especially in neonates.