Background: Methemoglobinemia is a rare cause of cyanosis in pediatric
patients and may arise as a result of a genetic defect in red blood cell metabolism or
hemoglobin structure, or it may be acquired following exposure to various oxidant drugs
or toxins. It is characterized by increased quantities of hemoglobin in which the iron of
heme is oxidized to the ferric (Fe3+) form.
Case Report: We describe a case of a premature infant who developed cyanosis after
dermal application of 1 gram of a eutectic mixture of lidocaine 2.5% and prilocaine 2.5%
ointment before the insertion of a central venous catheter for parenteral nutrition. Eight
hours after dermal application, his methemoglobin levels were 24.6% and was given an
intravenous methylene blue infusion which promptly cleared his cyanosis and restored
tissue oxygenation. The samples were analyzed for methemoglobin reductase enzyme
activity. The initial enzyme activity level was 14.8 IU/g. Seven months later, the activity
level of methemoglobin reductase was repeated and resulted normal (25.7 IU/g).
Conclusion: We conclude that a light inadvertent miscalculation of the dose can lead to
serious adverse effect, such as in our case. Because preterm neonates are easily overdosed
for low weight routinely use of EMLA should be carefully evaluated.