What is the Difference Between Lidocaine and Tetracaine?

Lidocaine and tetracaine are both topical local anesthetics used to cause numbness or loss of feeling in the skin during various medical and aesthetic procedures. However, they have some differences in their properties and actions:

1. Class: Lidocaine is an amide-type local anesthetic, while tetracaine is an ester-type local anesthetic.
2. Lipophilicity: Tetracaine is more lipophilic than lidocaine, concentrating in the stratum corneum of the epidermis, where it slowly diffuses.
3. Duration: Tetracaine has a longer duration of action compared to lidocaine due to its slow diffusion and limited systemic uptake.
4. Stability: Lidocaine is more stable in solution and can be stored for longer periods, while tetracaine is less stable and unstable in heat.
5. Metabolism: Tetracaine is metabolized rapidly by plasma esterase and has a very short life, whereas lidocaine is broken down slowly in the liver by amidases, resulting in a longer half-life.
6. Relative Potency: Lidocaine has a relative potency of 4, while tetracaine has a relative potency of 10.

Despite these differences, both lidocaine and tetracaine are widely used in medical and aesthetic procedures to reduce pain signals by blocking the conduction of nerve impulses at the level of the skin.

Comparative Table: Lidocaine vs Tetracaine

Lidocaine and tetracaine are both local anesthetics, but they have some differences in their chemical structure and potency. Here is a table comparing the two:

Lidocaine is an amide-based local anesthetic, while tetracaine is an ester-based local anesthetic. Lidocaine has a relative potency of 4, meaning it takes 4 times the amount of lidocaine to achieve the same level of anesthesia as tetracaine, which has a relative potency of 10.

The melting points of lidocaine and tetracaine differ, with lidocaine having a higher melting point. When both local anesthetics are applied topically, their systemic levels in the plasma are below 0.5 ng/mL for both lidocaine and tetracaine.