Term
| main use of local anesthetics |
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Definition
| to prevent or abolish "unpleasant sensations" (usually pain) in a relatively discrete region of the body |
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Term
| characteristics of an "ideal" local anesthetic |
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Definition
fast onset and duration of action "just right" for intended use
good potency (no need for lots of parenteral administration)
safe - few SE, low toxicity risk
non-allergenic
no adjuncts needed |
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Term
| 2 main chemical classes of local anesthetics |
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Definition
ALL: "-caine"
1. esters
prototype = PROCAINE
(only 1 "i")
2. amides
prototype: LIDOCAINE
(2 "i"'s) |
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Term
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Definition
prototype ester local anesthetic
rarely used because of low potency, slow onset, short duration of action and relatively high allergenicity
used less often than amide anesthetics
inactivated and detoxified by plasma esterases
other drugs in this class are esters with different pharmacokinetics and potency |
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Term
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Definition
prototype amide local anesthetic
most widely used local anesthetic (closest to "ideal")
*metabolized in the liver*
relatively low allergenicity |
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Term
general principles of local anesthetics
mechanism |
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Definition
LAs work intra-neuronally and so must diffuse through the membranes that surround the neuron
LAs are weak bases (pKa=8-9)
UNcharged LA molecules can diffuse across neuronal membrane to reach site of action
block Na channels and depolarization of sensory nerves; suppression of local neuronal activity
no effect on resting nerves |
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Term
| effect of local ischemia on local anesthetic action |
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Definition
tissues w/o adequate blood flow tend to be acidotic
LA molecules stay in ionized/charged form in low pH setting
can't diffuse to site of action in charged form |
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Term
| location of local anesthetic targets |
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Definition
have ability to effect ALL excitable tissues (nerve, muscle)
small diameter > large diameter
non myelinated > myelinated
rapidly firing > slow firing > resting |
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Term
local anesthetics
metabolism |
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Definition
the UNmetabolized parent drug is responsible for desired effects (and most toxic effects)
more potent, faster, longer acting LAs --> greater risk of toxicity than less potent, slower, shorter acting drugs |
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Term
local anesthetics
mechanism of toxicity |
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Definition
dose (blood level) dependent
caused by unmetabolized drug (parent)
influenced by metabolic capacity of liver (amides) and plasma esterases (esters) |
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Term
local anesthetics
signs and symptoms of toxicity |
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Definition
CV depression leading to decreased CO
medullary/ventilatory depression
progressive CNS stimulation that can lead to status epilepticus
*apnea during seizures in the main cause of death* |
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Term
local anesthetics
cardio(vascular)toxicity |
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Definition
block cardiac Na channels decreasing automaticity, rate, conduction velocity, regratoriness and inotropic state (except cocaine)
vasodilator: vascular smooth muscle relazation, decreased TPR (except cocaine) |
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Term
| local anesthetics and IV administration |
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Definition
IV lidocaine and be used for certain cardiac arrhythmias (NO analgesic purpose)
IV LA for analgesia may be used by trained professionals to provide anesthesia to an entire limb (dangerous process)
NO use as general anesthetic |
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Term
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Definition
preparation of parenteral LA pre-mixed with vasoconstrictors act to prevent local blood flow of the target area from washing away LA from site of infiltration
usually EPI
slows systemic absorption of LA: faster onset, longer duration, increased intensity, decreased risk of systemic toxicity
*NO decreased risk of allergic reaction or reaction severity* - very small amount of EPI (even safe for HTN patients)
XX: avoid use in areas with "one way IN/OUT" for blood flow to avoid ischemic risk (e.g. fingers) |
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Term
local anesthetics
allergenicity |
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Definition
varies between classes
more common with esters
cross-reactivity within-class |
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Term
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Definition
ester for topical use only
can't ionize well at physiologic pH
hydrolyzed to PABA |
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Term
benzocaine
uses, limitations, concerns |
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Definition
indicated for short-term use on small areas of skin, mucous membranes
marginally affective on intact skin; should NOT be used on broken skin
excessive topical use can cause drug-induced dermatitis prolonged s/sx and leading to more (mis)use |
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Term
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Definition
ester
commonly used topically when anesthesia and hemostasis are needed (eye, nose, throat some cosmetic surgeries)
cerebral cortical stimulant
blocks neuronal NE reuptake
sympathomimetic effects, vasoconstriction |
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