Abstract
Acquired methemoglobinemia is an uncommon hemoglobinopathy that results from exposure to oxidizing agents, such as chemicals or medications. Although, as reported in the adult population, it happens most often due to prescribed medication or procedural anesthesia and not due to easily accessed over-the-counter medications, the authors will describe an otherwise healthy male adult with no known medical history and no prescribed medications, who presented to the emergency department reporting generalized weakness, shortness of breath, headache, dizziness, and pale gray skin. In addition, the patient reported that he also had a severe toothache for several days, which he had been self-treating with an over-the-counter oral benzocaine gel. Ultimately, the diagnosis of methemoglobinemia was made by clinical history, physical examination, and the appearance of chocolate-colored blood and arterial blood gas (ABG) with cooximetry. After 2 mg/kg of intravenous methylene blue was administered, the patient had complete resolution of all signs and symptoms. This case illustrates that emergency physicians should be keenly aware of the potential of toxic hemoglobinopathy secondary to over-the-counter, nonprescribed medications. Discussion with patients regarding the dangers of inappropriate use of these medicines is imperative, as such warnings are typically not evident on product labels.
Highlights
Acquired methemoglobinemia is typically caused by oxidative stress and many prescribed medications are strongly associated with inducing methemoglobinemia (Table 1) [1, 2]
It is so rare for methemoglobinemia to be acquired in this fashion, that, in a 2013 study, with 576 participants, evaluating the efficacy of self-applied, over-thecounter oral benzocaine gel, there was no incidence of methemoglobinemia, even after a 1,026 mg administration by one participant in a two-hour period [5]
Acquired methemoglobinemia is due to the exposure to an oxidizing chemical or drug (Table 1), leading to the removal of an electron from ferrous hemoglobin (Fe2+) to create ferric hemoglobin (Fe3+) at a rate that surpasses the endogenous reducing mechanisms, which primarily include the enzymatic activity of cytochrome b5 reductase and nicotinamide adenine dinucleotide (NADH) methemoglobin reductase [1,2,3, 6]
Summary
Acquired methemoglobinemia is typically caused by oxidative stress and many prescribed medications are strongly associated with inducing methemoglobinemia (Table 1) [1, 2]. The authors report a rare case of an otherwise healthy adult patient who presents with methemoglobinemia after self-administering over-thecounter topical benzocaine gel. Prilocaine Quinones (e.g., chloroquine) Rifampin Sulfonamides (e.g., sulfamethoxazole) to the emergency department with a chief complaint of generalized weakness since the previous evening He reported dyspnea, headache, and dizziness, which started the day of presentation, and his coworkers noted his skin to be pale and grayish in appearance. The patient reported that he had a toothache for several days and was self-treating with an over-the-counter topical medication, Maximum Strength Orajel (benzocaine) (Figure 1) He stated he had been applying the gel three times per day for three days.
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
