Benzocaine Causes Methemoglobinemia—a Rare Disorder That Turns Blood Blue

It's scary to have to go to the emergency room to get help for a medical condition. When a 25-year-old sought help at an emergency room for symptoms of fatigue, shortness of breath, generalized weakness, and skin discoloration, they received news that even the doctors themselves weren't expecting—their blood was actually turning blue.

The Methemoglobinemia Case Study

The strange case is featured in a report published in the New England Journal of Medicine. According to the report, the patient came to the ER appearing cyanotic—that's the clinical term for appearing to have a blue tint to the skin. They also presented with a high respiratory rate of 22 breaths per minute. The U.S. National Library of Medicine says that a typical breathing rate for adults at rest is eight to 16 breaths per minute. They also had an oxygen saturation of 88%, which essentially meant they weren't getting enough oxygen in their blood. The typical oxygen saturation rate is 95–100%.

Doctors eventually discovered that the patient's blood was blue and finally diagnosed her with a condition called methemoglobinemia. We got the facts about this rare but potentially fatal condition.

A Rare Disorder

So, methemoglobinemia is a rare blood disorder that causes people to produce an abnormal amount of methemoglobin. Just FYI: Methemoglobin is a type of hemoglobin or a protein found in red blood cells which is responsible for transporting oxygen via blood. With methemoglobinemia, the body's hemoglobin is able to carry oxygen, but cannot deliver it to the body's tissues, per the U.S. National Library of Medicine (NLM).

Methemoglobinemia can be inherited, or it can be caused by specific medicines, foods, or chemicals, the NLM reports. The patient featured in the new case report developed methemoglobinemia after using medication to treat a toothache. The topical medication she used contained benzocaine, a local anesthetic or numbing agent and active ingredient found in over-the-counter toothache and cold sore medicine.

Caused by Benzocaine

This isn't the first time a product used to relieve mouth pain has been linked to methemoglobinemia. Last year, a mom in Virginia reported that, after giving her 15-month-old Orajel Instant Relief for Teething Pain, the child became unresponsive and stopped breathing.

Shortly thereafter the FDA updated a statement on benzocaine, advising parents not to administer "over-the-counter oral drug products containing benzocaine" to children under two years old. "Benzocaine…can cause a condition in which the amount of oxygen carried through the blood is greatly reduced. This condition, called methemoglobinemia, can be life-threatening and result in death," the statement says.

Luckily, the patient in the new case report had doctors identify her methemoglobinemia in time and she was given a medication called methylene blue (which, fittingly, is a medication and a blue dye), used to help patients' blood better distribute oxygen. The patient made a complete recovery.