21: Local Anesthetics Flashcards
how do topical anesthetics work?
they are surface-acting drugs that produce a reversible inhibition of the sensory nerve endings within the corneal and conjunctival epithelium, producing transient local anesthesia of the corneal and conjunctival surfaces
what can topically applied anesthetics cause transiently?
-irregularity of the corneal epithelium and corneal disruption can interfere with subsequent procedures requiring visualization inside the eye, such as funds photography
what should be measured before topical anesthesia
tear break up time
does epinephrine and vasoconstrictors have any effect on topical anesthesia
no significant effect on the duration of topical anesthesia (shouldn’t be combined)
-only epi. is used with local infiltrative injections like in dentistry
describe how local anesthetics are reversible
reversible conduction blockade of nerve impulses, therefore, the effects of local anesthetics are completely reversible, without any evidence of structural damage to nerve fibers
the 2 ways in which local anesthetics produce anesthesia?
by inhibiting excitation of nerve endings or by blocking conduction in peripheral nerves
how does local anesthesia interact with sodium channels ?
- reversible binding and inactivation of sodium channels
- sodium influx through these channels is necessary for the depolarization of nerve cell membranes
- when a nerve loses depolarization and capacity to propagate an impulse, the individual loses sensation in the area supplied by the nerve
what is the main way local anesthetics prevent the generation and conduction of nerve impulses?
-reducing sodium permeability
what are the 3 distinct structural components of local anesthetics
- aromatic lipophilic portion
- an intermediate alkyl chain or linkage (determines anesthetic class)
- hydrophilic amine group
what structural component determines the class of anesthetic agent?
the intermediate linkage
what does the intermediate linkage determine?
determines metabolism and other pharmacological properties
what is PABAs role?
PABA esters metabolized in the plasma by esterases
amides are metabolized by the
liver
all topically-applied anesthetic agents are what class
esters (except for lidocaine)
most injectable anesthetic agents are what class
amides
in the middle of the structural components is a link or chain which is either an ___ or an ____
an ester or an amide
3 options for linked to the aromatic group by an ester
- ester of PABA
- ester of meta-aminobenzoic acid
- ester of benzoic acid
list 2 ophthalmic preparations that are esters of PABA
- tetracaine
- benoxinate (also in combo with fluorescein)
list 2 ophthalmic preparations that are esters of meta-aminobenzoic acid
- proparacaine (wide use, comfort, less corneal compromise)
- proparacaine and fluorescein (Flucaine)
list an example of an amide of benzoic acid
-lidocaine (Atken): an ophthalmic gel product
allergic reactions to local anesthetics occur almost exclusively with which group?
to those with an ester linkage (PABA derivatives)
although anesthetics in current ophthalmic use have relatively low systemic and ocular toxicity, what are some possible adverse effects?
- allergic reactions (both local and systemic)
- CNS stimulation
- cardiovascaular stimulation
describe the mechanism of action of local anesthetics
stabilize neuronal membrane so the neuron is less permeable to sodium ions, preventing the initiation and transmission of nerve impulses
compare/contrast proparacaine and tetracaine
- approximately equipotent
- both have rapid onset of anesthesia (within 10-20seconds)
- duration of action (10-20 mins)
- proparacaine may have slightly faster onset/longer duration
