8.5: Local Anesthetics: Common Agents and Their Applications
Local anesthetics (LAs) are commonly used for various applications in medical and dental procedures. Some of the common agents used are cocaine, lidocaine, and bupivacaine.
Cocaine is an ester of benzoic acid and methylecgogine. It is used to anesthetize and vasoconstrict locally. Currently, it is used primarily for topical applications. It is beneficial for surgeries on the upper respiratory tract, providing anesthesia and shrinking the mucosa. Cocaine in the form of cocaine hydrochloride is available in the market as 1%, 4% and 10% solutions. The 1% and 4% solutions are most commonly used as it reduces toxicity. High toxicity and abuse of cocaine have led to its reduced use in the clinic.
Lidocaine is an amide-linked LA with a wide range of applications. It can be formulated for injections as well as topical, ophthalmic, mucosal, and transdermal uses. Lidocaine can be used as a single agent or in combination with other agents such as prilocaine and tetracaine. It produces faster and long-lasting anesthesia. Although lidocaine is effective and can be administered without adding vasoconstrictors, it readily escapes into the systemic circulation from the muscles, GI and respiratory tracts. Adding vasoconstrictors like epinephrine can constrict the blood vessels, reducing absorption and systemic toxicity.
Bupivacaine is also an amide-linked LA with a wide range of applications. It is used in applications where a prolonged anesthesia duration is required. Bupivacaine tends to block the sensory fibers more than the motor fibers. It can be infused continuously through catheters to provide adequate anesthesia for several days.
