Unlike other drugs which act in the region of the synapse,
local anesthetics are agents that reversibly block the generation
and conduction of nerve impulses along a nerve fiber. They depress
impulses from sensory nerves of the skin, surfaces of mucosa,
and muscles to the central nervous system. These agents are widely
used in surgery, dentistry, and ophthalmology to block transmission
of impulses in peripheral nerve endings.
Most local anesthetics can be represented by the following
general formula. In both the official chemical name and the proprietary
name, a local anesthetic drug can be recognized by the "-caine"
The ester linkage can also be an amide linkage. The most recent
research indicates that the local anesthetic binds to a phospholipid
in the nerve membrane and inhibits the ability of the phospholipid
to bind Ca+2 ions.
Practically all of the free-base forms of the drugs are liquids.
For this reason most of these drugs are used as salts (chloride,
sulfate, etc.) which are water soluble, odorless, and crystalline
solids. As esters these drugs are easily hydrolyzed with consequent
loss of activity. The amide form of the drug is more stable
and resistant to hydrolysis.