Hi Lisa!

Thanks for your question. Scott Robinson MD and Nataliya Lebedinskaya RN, BSN, CWOCN and I discussed your question - while benzocaine is an option for topical anesthesia prior to conservative sharp wound debridement, there are other options that are often used such as lidocaine 2-5% gel. After 5-10 minutes, patients may be ready for the procedure. If initial efforts at topical anesthesia fail, injectable lidocaine can be used, which should be easier to inject due to partial numbing in the area from the previous gel application. Benzocaine can be an alternative if contraindication to lidocaine exists, as it is an ester-type ester-type local anesthetic.[1] For choice of technique and local anesthetic agent in wound care, see topic "How to Administer Local Anesthesia for Wound Care Procedures" at https://woundreference.com/app/topic?id=how-to-perform-subcutaneous-infiltrations-of-local-anesthetics#selection-of-local-anesthesia-for-wound-care

As for the controversy on the use of benzocaine: benzocaine is often used as a spray for topical anesthesia of mouth and throat, and is not readily absorbed into the systemic circulation. Benzocaine is relatively safe and low-risk when applied topically. Benzocaine gels and liquids are sold OTC under different brand names such as Anbesol, Hurricaine, Orajel, Baby Orajel, Orabase, and store brands.

Controversy regarding the use of benzocaine has been described due to the fact that benzocaine spray is not totally innocuous and can result in methemoglobinemia. In 2006 the FDA issued a health advisory to warn healthcare professionals of the risk for methemoglobinemia associated with use of benzocaine sprays.[2] In the cases, topical benzocaine spray was used for medical procedures such as transesophageal echocardiogram, endoscopy, bronchoscopy, intubation, and feeding tube placements.

Methemoglobinemia is a condition whereby the typically ferrous (Fe+2) state of iron, which is functional for oxygen transport, is oxidized to the ferric (Fe+3) state. This results in a nonfunctional hemoglobin that is incapable of binding to oxygen and may cause hypoxemia.[3] Even though it has been estimated that only 1 in 7000 exposures to benzocaine may result in methemoglobinemia [3] some authors concluded that benzocaine should not be used. [3] An accompanying editorial underlined the importance of avoiding benzocaine, because of an “inability to predict potentially fatal events relating to the use of this drug” [4] Should symptomatic methemoglobinemia occur, treatment includes supplemental oxygen and methylene blue 1 to 2 mg/kg IV given over 5 minutes.[5]

FDA recommendations for clinicians regarding benzocaine spray include [2]:
- Before recommending benzocaine products, discuss the signs and symptoms of methemoglobinemia with your patients. Advise patients to monitor for signs and symptoms when using benzocaine products, and to seek medical attention immediately if they suspect methemoglobinemia.
- Recognize the signs and symptoms of methemoglobinemia, including pale, gray or blue colored skin, lips, and nail beds; headache; lightheadedness; shortness of breath; fatigue; and tachycardia. These indicate a moderate to severe level of methemoglobin and a marked reduction in the oxygen-carrying capacity of the blood. A characteristic color of the blood (chocolate-brown rather than blood red) may indicate methemoglobinemia, but this change is a late sign of the condition. Symptoms may appear within minutes to one or two hours after using benzocaine.
- Symptoms may occur with the first or subsequent applications of benzocaine.
- Methemoglobinemia can cause unreliable oxygen saturation readings on a standard 2-wavelength pulse oximeter when used to assess the amount of oxygen bound to hemoglobin. If blood is drawn to check for methemoglobinemia, an FDA approved co-oximeter should be used to reliably measure methemoglobin.
- Patients who have breathing problems such as asthma, bronchitis, or emphysema, patients with heart disease, and patients who smoke are at greater risk for complications related to methemoglobinemia.
- Infants less than four months of age, elderly patients, and patients with certain inborn defects such as glucose-6-phosphodiesterase deficiency, hemoglobin-M disease, NADH-methemoglobin reductase (diaphorase 1) deficiency, and pyruvate-kinase deficiency may also be at greater risk of developing methemoglobinemia.
- Medications, foods, and water containing nitrites and nitrates may also induce methemoglobin formation that will be additive to that formed by benzocaine products.

[1] https://www.hmpgloballearningnetwork.com/site/podiatry/emerging-insights-wound-care-and-pain-management
[2] https://www.fda.gov/drugs/drug-safety-and-availability/fda-drug-safety-communication-reports-rare-serious-and-potentially-fatal-adverse-effect-use-over#:~:text=If%20benzocaine%20products%20are%20used,lightheadedness%3B%20and%20rapid%20heart%20rate
[3] https://www.sciencedirect.com/science/article/abs/pii/B9780323608268000079
[4] https://www.sciencedirect.com/science/article/pii/B9780444537416000118
[5] https://www.sciencedirect.com/science/article/pii/B9781437727647000117