Anesthesiology/Spray topical LAST


Hi I was wondering can a topical benzocaine spray cause Local anaesthetic toxicity ? And if so does this mean the spray can cause nerve damage?

Hi there

Great question!

Over the counter sprays are less likely to cause Methemoglobinemia  but unlikely to ever cause LA toxicity. However at massive doses they can. Over-the-counter products advertised as toothache relief and baby-teething gels, sting relief formulas, pain relief sprays, hemorrhoidal creams, and vaginal and rectal suppositories. These preparations contain benzocaine in concentrations varying from 5% to 20%. They provide symptomatic relief of anal and genital pruritus, skin rashes, dermatoses, and toothaches.

Benzocaine is available in spray form, throat lozenges, and liquid and gel preparations. Benzocaine spray is prepared as a 14% to 20% concentration. As stated in the dosing instructions for topical benzocaine,[11] it should not be sprayed for more than 1 second, and spraying for more than 2 seconds is considered contraindicated. Average expulsion rate is 200 to 295 mg/sec.

Methemoglobinemia is a disorder characterized by the presence of a higher than normal level of methemoglobin (metHb, i.e., ferric [Fe3+] rather than ferrous [Fe2+] hemoglobin) in the blood. Methemoglobin is a form of hemoglobin that contains ferric [Fe3+] iron and has a decreased ability to bind oxygen. However, the ferrous iron has an increased affinity for bound oxygen. The binding of oxygen to methemoglobin results in an increased affinity of oxygen to the three other heme sites (that are still ferrous) within the same tetrameric hemoglobin unit. This leads to an overall reduced ability of the red blood cell to release oxygen to tissues, with the associated oxygen–hemoglobin dissociation curve therefore shifted to the left. When methemoglobin concentration is elevated in red blood cells, tissue hypoxia can occur.

So if you follow as directed there is negligible risk. As for nerve damage, that would be extraordinarily rare and i found no info on it.

See this articles on it:

Hope this helps!


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Mike MacKinnon MSN FNP-C CRNA


I am a former Trauma Flight RN now a Family Nurse Practitioner and a Nurse Anesthetist (CRNAs). I can help answer questions on the CRNA profession and clinical anesthesia. I work full time as an independent practice CRNA and have a special interest in regional anesthesia, particularly peripheral nerve blocks. I also teach ultrasound regional anesthesia and lecture all over the country. If I do not know the answer, I will find it for you.


I am a Family Nurse Practitioner and a Nurse Anesthetist who works as an independent/autonomous practitioner. There are often questions about my profession and I would like to offer the service of an actual CRNA. If you did not know, there are about 40000 of us which equates to 50% of the anesthesia providers in the USA today. I also lecture and teach ultrasound regional anesthesia all over the country.

AANA (American Association of Nurse Anesthetists)
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Air Medical Transport Journal
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