Final answer:
Local anesthetics are divided into amide and ester types, with ester linkages being more prone to hydrolysis leading to rapid inactivation in the body. Procaine, an ester anesthetic, has variable potency and toxicity based on changes in its structure. Ethyl chloride is an external local anesthetic that works by cooling the skin.
Step-by-step explanation:
Amide vs Ester Local Anesthetics
Local anesthetics can be categorized into two types based on the nature of the chemical bond connecting their hydrophilic and hydrophobic domains: amide and ester anesthetics. An important difference between the two is the stability of their chemical linkage in the body. Ester anesthetics have a bond that is easily hydrolyzed, leading to rapid metabolic degradation and inactivation. A classic example of an ester anesthetic is procaine, which consists of three main parts: an aromatic acid (para-aminobenzoic), an alcohol (ethanol), and a tertiary amino group (diethylamino). Altering any portion of procaine can change both its anesthetic potency and toxicity. For instance, increasing the length of the alcohol group enhances anesthetic potency but also increases toxicity.
On the other hand, ethyl chloride functions as an external local anesthetic by a different mechanism. When applied topically and sprayed on the skin, it evaporates, causing a cooling effect that results in a loss of pain sensitivity in the area. Ethyl chloride can sometimes be utilized in emergency situations as a general anesthetic.