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 ropivacaine)
· “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.)