By Emma Yasinski
A woman made headlines last month when she arrived at the hospital, weak and literally blue. The case was reported in the New England Journal of Medicine.
It turned out she had a dangerous and potentially fatal condition called methemoglobinemia, likely as a result of using a topical pain reliever for a toothache. Luckily, doctors were able to reverse the condition in the emergency room and the woman recovered, but how could something like a topical pain reliever used on the teeth turn a woman blue and put her life in danger?
Methemoglobinemia is an extremely rare occurrence.
Gentry Wilkerson, MD, an emergency medicine doctor at the University of Maryland School of Medicine, told Incisor that “it is a very rare entity that many [healthcare professionals] will go their entire career without seeing.” Normally, oxygen binds to iron, which can carry it through the bloodstream. But, certain drugs can cause the iron to change shape. When that happens, the cells can still bind to and carry oxygen, but can’t distribute it to tissue. This turns the blood blue.
A healthy individual will have nearly 100 percent oxygen saturation, but a person experiencing methemoglobinemia will have far less. The woman in the case study showed 88 percent saturation in a test—which was cause for concern—but upon completing a more specific test, it was shown to be even lower: 67 percent.
Dr. Wilkerson warned that sometimes the disease can be refractory; the person’s oxygen saturation will hover around a dangerous 85 percent, even after they’re administered oxygen.
In dental analgesics, the ingredient responsible for the disease is benzocaine, which is found in a variety of over-the-counter and prescription medications. In 2018, the FDA warned consumers about using benzocaine-containing products, especially in children under the age of two, due to the risk of methemoglobinemia. The statement said that 119 cases of the illness were reported to the FDA, eleven of which were in children under two, between 2009 and 2017.
The statement specified: “Benzocaine products are marketed as gels, sprays, ointments, solutions, and lozenges under brand names such as Anbesol, Orabase, Orajel, Baby Orajel, Hurricaine, and Topex, as well as store brands and generics. Prescription local anesthetics include articaine, bupivacaine, chloroprocaine, lidocaine, mepivacaine, prilocaine, ropivacaine, and tetracaine.”
But benzocaine is not the only ingredient that can cause methemoglobinemia. “A number of medications can cause acquired methemoglobinemia,” said Dr. Wilkerson. Prilocaine, another type of topical analgesic used on the skin, can cause the illness, as can nitrates and antibiotics such as dapsone. “If there is concern for methemoglobinemia, the patient should be taken to an Emergency Department for evaluation and treatment. High methemoglobinemia can be fatal,” he said.
Author: Contributing writer Emma Yasinski received her Master of Science (MS) in science and medical journalism from Boston University. Her articles have also appeared at TheAtlantic.com, Kaiser Health News, NPR Shots, and Genetic Engineering and Biotechnology News.
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