Local Anesthetics: Common Agents and Their Applications

Local anesthetics or LAs are commonly used for various applications ranging from topical pain relievers such as cough lozenges to intravenous injections.

Topical agents like dyclonine and pramocaine are rapidly absorbed through the mucous membranes and the skin. Although the anesthesia is short-lived, these drugs have popular over-the-counter applications as lozenges, sprays, patches, and gels.

Topical LAs with low aqueous solubility, such as benzocaine, can be applied directly to wounds, where they remain localized and produce a sustained effect.

Most topical anesthetics are irritants and cannot be directly applied to sensitive areas like the eyes. LAs for ophthalmic use, such as proparacaine and tetracaine, are applied as a single drop at a time.

The duration of anesthesia depends on tissue vascularity. It is longest for normal cornea and shortest for inflamed conjunctiva, which requires repeated applications.

Nerve-blocking LAs such as lidocaine and bupivacaine are used for prolonged anesthesia and pain control. Because they cause severe transient neurologic pain, these are only used at low concentrations.