Local anesthetics are administered to prevent or relieve pain
in aspecific area of the body. In addition, these drugs are often used as an
alternative to general anesthesia for elderly or debilitated patients.
Local anesthetics may be:
“amide” drugs (with nitrogen in the molecular chain, such as
bupivacaine, levobupivacaine, lidocaine, mepivacaine, prilocaine, and
“ester” drugs (with oxygen in the molecular chain, such as
chloroprocaine, cocaine, procaine, and tetracaine). (See Amidesand esters.)
Absorption of local anesthetics varies widely, but
distribution oc-curs throughout the body. Esters and amides undergo different
types of metabolism, but both yield metabolites that are excreted in the urine.
Local anesthetics block nerve impulses at the point
of contact in all kinds of nerves. They accumulate, causing the nerve cell
mem-brane to expand. As the membrane expands, the cell loses its abil-ity to
depolarize, which is necessary for impulse transmission. (See Blocking the pain pathways.)
Local anesthetics are used to prevent and relieve
pain from med-ical procedures, disease, or injury. Local anesthetics may also
be used for severe pain that topical anesthetics or analgesics can’t re-lieve.
Local anesthetics are usually preferred to general
anesthetics for surgery in an elderly or debilitated patient or a patient with
a dis-order that affects respiratory function, such as chronic obstruc-tive
pulmonary disease and myasthenia gravis.
For some procedures, a local anesthetic is combined
with a drug that constricts blood vessels, such as epinephrine. Vasoconstric-tion
helps control local bleeding and reduces absorption of the anesthetic. Reduced
absorption prolongs the anesthetic’s action at the site and limits its
distribution and CNS effects.
Local anesthetics produce few significant interactions
with other drugs. They can, however, produce adverse reactions. (See Ad-verse reactions to local anesthetics.)