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21 Cards in this Set

  • Front
  • Back
local anesthetics: definition
-produce a reversible loss of senstaion
-in a localized part of the body...
-when applied directly onto nerve tissue or mucous membranes
-local due only to the route of administration
ideal properties of a local anesthetic
-rapid onset of action
-duration of action appropriate for the intended purpose
-brief, reversile block of nerve conduction
-low degree of local and systemic toxicity
-water soluble and stable in solution
classes of local anesthetics
a) ester
-cocaine
-procaine
-benzocaine
-tetracaine
b) amide
-lidocane
-mepivicaine
-bupivacaine
-ropivacaine
MOA
prevent the generation and conductino of nerve impulses by decreasing/preventing the large transient increase in sodium permeability produced by membrane depolarization
local anesthetics are weak bases
have a pKa of 8-9

severe infections and inflammation tend to lower the local pH
-more drug is required to obtain desired anesthesia

decreased pH = decreased potency, increases drug required
increased pH= increased potency, decreased drug required
sensitivity to local anesthetics depends on:
-fiber diameter
-fiber type
-degree of myelination

-unmylelinatied fibers more sensitive to local anesthetics

-sensory modalities are effected in the following order
pain
temp
touch
deep pressure
motor
pharmacokinetics--systemic absorption of local anesthetics is modified by several factors
1. dosage
2. site of injection
3. vasodilator properties

vasoconstrictors (like epi) are used to decrease the rate of systemic absorption
metabolism of local anesthetics
ester- hydrolyzed and inactivated by plasma pseudocholinesterase

amide- degraded hepatically by cytochrome P450
toxicity
CNS
-low systemic concentrations: sleepiness, light-headedness, visual and auditory disturbances, restlessness
-high systemic concentrations: convulsions, seizures, CNS depression, death

CV
-block cardiac Na channels causing arrhythmic, depressed contraction , hypotension, and CV collapse

PNS
can be toxic to the nerve tissues
allegic reactions to local anesthetics
more in ester family due to the metabolism into paraamino benzonate (PABA)

symptoms may include:
-skin reactions (rashes, itching, edema, or hives)
-asthma-like symptoms
-in the most extreme cases anaphylactic shock may occur
Uses
-surface anesthesia
-infilatration anesthesia (aspirate prior to injections)
-nerve block
-spinal anesthesia
-epidural anesthesia
cocaine
ESTER
-rapid onset with a long duration of action
-used exclusively for topical application
-only local which produces vasoconstriction (result of inhibition of NE reuptake)
-OD noted by excitement, restlessness, confusion, and tremor
procaine (novocaine)
ESTER
-short duration of cancer
-greatest vasodilator of all local anesthetics
-first synthetic local
-high incidence of allergy
benzocaine
ESTER
-used topically only due to poor solubility in water, poor absorption, and is high toxicity if absorbed
-localized allergic reactions
tetracaine
ESTER
-slow onset with long duration of action
-highly water soluble and therfore can be used topically and/or injected
-great potential for systemic toxicity
-widely used in spinal anesthesia
lidocaine
AMIDE
-gold standard for local anesthetics
-rapid onset with intermediate duration of action
-overdose marked by drowsiness, loss of consciousness and respiratory arrest
mepivacaine
AMINE
-rapid onset with intermediate duration of action
-produces slight vasodilation
-increased toxicity in neonates (decrease in blood pH)
-not used as a topical agent
bupivacaine
-rapid onset and long duration of action
-significant vasodilatory properties
ropivacaine
-long duration of action
-slightly less potent through significantly less CV relative to other local anesthetics
-slower uptake resulting in a lower blood level of any given dose
other drugs with local anesthetic effects
antihistamine (diphenhydramine)

antidepressant (tricyclics)
drug interactions
-antihistamines
-antiarrhythmics
both synergystc

-sulfonamide antibiotics
-cholinesterase inhibitors