Chemistry at Home - Lidocaine by Ephraim Ng

Lidocaine is a chemical that is used as a local anesthetic and numbing agent¹. It is

commonly found at home in Polysporin® and pain relief patches. The lidocaine in

Polysporin® minimizes the amount of pain from cuts and scrapes². Lidocaine is also found at the dental office since it is used as a freezing agent during cavity fillings and oral surgeries³. With lidocaine being a commonly used household product, health and safety concerning this chemical is very important. The oral LD50 of lidocaine in mice is 292 mg/kg⁴. To put this into perspective, a 30 g tube of Polysporin® contains 1.5 grams of lidocaine. If we assume humans have an LD50 similar to mice, it would require eating 13 tubes of Polysporin® to have a 50% chance of killing a 70 kg human from lidocaine overdose. This isn’t the intended use for Polysporin®, if used properly, there is no way to receive such a high dose of lidocaine. Lidocaine is very safe if used for its intended purpose.  

Lidocaine’s structure is composed of mainly carbons and hydrogens and one each of

oxygen and nitrogen¹. The discovery of lidocaine dates back to the 1930s when a scientist

Euler-Cheplin isolated a compound from a mutant strain of barley named gramine⁵.

Euler-Chelpin’s colleague, Erdtman, was able to modify the arrangement in its chemical

structure and named this new compound isogramine⁵. Erdtman tasted this compound

and found that it made his tongue numb (don’t do this in the lab, it is super dangerous)⁵.

Knowing this, the scientists modified the structure of the chemical further and eventually

synthesized lidocaine which became the new standard for local anesthesia⁵. Mass lidocaine production is done by reacting small molecules together to form the larger lidocaine molecule⁶. 

There aren’t many controversies surrounding lidocaine but pain relief patches

shockingly don’t have any clinical evidence of being able to relieve arthritis related pain⁷.

Capsaicin creams and oral painkillers are better at relieving this kind of pain⁷. Lidocaine

is a very safe chemical; I would have no problems with my dentist using lidocaine and

will continue to use Polysporin®. You won’t catch me using the pain relief patches though.

1. Lidocaine. (n.d.). Retrieved from https://pubchem.ncbi.nlm.nih.gov/compound/Lidocaine#section=2D-Structure
2. Lidocaine - brand name list from Drugs.com.(n.d.). Retrieved from https://www.drugs.com/ingredient/lidocaine.html
3. Nordqvist, J. Uses, types, and risks of local anesthesia. (2017). https://www.medicalnewstoday.com/articles/265689.php#uses
4. ONeil, M. J., Heckelman, P. E., & Dobbelaar, P. H. (2013). The Merck index: an encyclopedia of chemicals, drugs, and biologicals. Cambridge, UK: Royal Society of Chemistry.
5. Gordh, T., Gordh, T. E., & Lindqvist, K. (2010). Lidocaine: The Origin of a Modern Local Anesthetic. Anesthesiology, 113(6), 1433–1437. doi: 10.1097/aln.0b013e3181fcef48
6. The synthesis of Lidocaine. (n.d.)  Retrieved from http://home.sandiego.edu/~khuong/chem302L/Handouts/Lidocaine_handout_Su07.pdf
7. Winter, G. (2018, October 2). The painful truth about lidocaine patches. Retrieved from https://www.irishtimes.com/life-and-style/health-family/the-painful-truth-about-lidocaine-patches-1.3640750