How does benzocaine cause methemoglobinemia

Benzocaine is a more powerful oxidizing agent than lidocaine in animal studies, and a dose-response relationship has been demonstrated between benzocaine and methemoglobin [ 10 , 11 ]. Another risk factor for developing pharmacologic-induced methemoglobinemia is concomitant illnesses, such as cardiac and respiratory diseases [ 12 ].

Concentration of methemoglobin is reported as the percentage of total hemoglobin. Although hemoglobin level does not directly affect the production of methemoglobin, it does affect the amount of functional anemia.

Our patient did have baseline anemia, which put him at a higher risk of developing more symptoms of methemoglobinemia. Infants are more susceptible than adults because hemoglobin F is more susceptible to oxidation [ 14 ]. In our case, the likelihood of an adverse drug reaction using the Naranjo probability scale was calculated to be probable score of 6 [ 15 ].

Our conclusion was based on previous reports on this reaction; the adverse event appearing after the suspected drugs were administered; the adverse reaction improving when the drugs were discontinued; the drug being detected in the blood in a toxic concentration, and confirmation with objective evidence.

Clinical symptoms and signs depend on the level of methemoglobin. The diagnosis of methemoglobinemia is made by analysis of an arterial blood sample, using co-oximetry, which demonstrates a discrepancy between a low arterial oxyhemoglobin saturation SaO 2 and a relatively high arterial oxygen partial pressure PaO 2.

A standard arterial blood gas analyzer measures the partial pressure of oxygen and calculates the oxygen saturation from this value. This is inaccurate because the methemoglobin level is assumed to be zero. However, a co-oximetry is a simplified spectophotometer that measure light absorbency at four different wavelengths and these wavelengths correspond to specific absorbency characteristics of deoxyhemoglobin, oxyhemoglobin, carboxyhemoglobin, and hemoglobin.

In the presence of methemoglobinemia, oxygenation obtained by pulse oximetry is inaccurate because it does not reflect the degree of desaturation and can under or over estimate oxygenation depending on the severity of methemoglobinemia. The diagnosis should be suspected if cyanosis develops suddenly after the administration of oxidizing agents, or if chocolate brown arterial blood does not turn red on exposure to air [ 2 ].

Methylene blue improves the efficiency of NADH methemoglobin reductase, and is an effective treatment for this condition. Improvement should occur within one hour, but if cyanosis persists, a second dose of methylene blue should be given [ 12 ]. Methylene blue itself has side effects, which include nausea, vomiting, diarrhea, dyspnea, burning sensation in the mouth and abdomen, restlessness, and perspiration. Therefore, methylene blue would lead to the formation of more methemoglobin because of its oxidant potential, leading to hemolysis [ 3 ].

Methemoglobinemia is a potentially severe complication of lidocaine and benzocaine, especially when used concomitantly. Among the acquired causes of methemoglobinemia, although caine-induced methemoglobinemia is rare, it may have a fatal outcome. Clinicians should, therefore, be familiar with this condition to ensure prompt diagnosis and effective treatment.

Our patient responded promptly with supplemental oxygen and this case demonstrates that methylene blue is not always necessary in the treatment of methemoglobinemia. SK wrote and revised the manuscript. All authors approved the final manuscript.

Consent for submission of this manuscript for publication has been given by the patient's wife. National Center for Biotechnology Information , U.

J Med Case Reports. Published online Jan Author information Article notes Copyright and License information Disclaimer. People with this type have a higher likelihood of developing acquired forms. Type 2 is also known as cytochrome b5 reductase deficiency. Type 2 affects all cells. Only one of your parents needs to pass on the abnormal gene. It can cause severe developmental problems and failure to thrive.

Babies born with type 2 usually die in their first year. This is also known as acute methemoglobinemia. Acquired methemoglobinemia is the most common type of the condition.

People who carry a genetic form of the condition have a higher chance of developing the acquired type. If acquired methemoglobinemia is not treated immediately, it can lead to death. Babies are most susceptible to this condition. Babies can develop acquired methemoglobinemia from:. The U. Food and Drug Administration recommends that parents and caregivers not use these OTC drugs on children younger than age 2. Contaminated well water: Infants younger than 6 months may develop acquired methemoglobinemia from contaminated well water that has excess nitrates.

Fully developed digestive systems keep children older than 6 months and adults from developing this nitrate poisoning.

Keep reading: Fertilizer and plant food poisoning ». Foods that might have too many nitrates include:. People have developed methemoglobinemia after having medical procedures that used certain topical anesthetics that are often sprayed on to the skin. These include benzocaine, lidocaine, and prilocaine. These may be used to:. Looking for more ways to calm your teething baby without using Orajel? If you want more information about Methemoglobinemia and teething gels, you can check out this news release from the American Dental Association.

It is important to remember that any drug that you give your child can have serious side effects. Make sure that you are an informed parent by learning about each drug you give your child — not just teething gels! Do you have any questions, comments, or concerns about methemoglobinemia and teething gels? Login Register. Continue Reading. Popular Emailed Recent Loading