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21 Cards in this Set
- Front
- Back
local anesthetics: definition
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-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 |
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ideal properties of a local anesthetic
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-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 |
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classes of local anesthetics
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a) ester
-cocaine -procaine -benzocaine -tetracaine b) amide -lidocane -mepivicaine -bupivacaine -ropivacaine |
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MOA
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prevent the generation and conductino of nerve impulses by decreasing/preventing the large transient increase in sodium permeability produced by membrane depolarization
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local anesthetics are weak bases
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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 |
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sensitivity to local anesthetics depends on:
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-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 |
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pharmacokinetics--systemic absorption of local anesthetics is modified by several factors
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1. dosage
2. site of injection 3. vasodilator properties vasoconstrictors (like epi) are used to decrease the rate of systemic absorption |
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metabolism of local anesthetics
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ester- hydrolyzed and inactivated by plasma pseudocholinesterase
amide- degraded hepatically by cytochrome P450 |
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toxicity
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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 |
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allegic reactions to local anesthetics
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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 |
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Uses
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-surface anesthesia
-infilatration anesthesia (aspirate prior to injections) -nerve block -spinal anesthesia -epidural anesthesia |
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cocaine
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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 |
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procaine (novocaine)
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ESTER
-short duration of cancer -greatest vasodilator of all local anesthetics -first synthetic local -high incidence of allergy |
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benzocaine
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ESTER
-used topically only due to poor solubility in water, poor absorption, and is high toxicity if absorbed -localized allergic reactions |
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tetracaine
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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 |
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lidocaine
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AMIDE
-gold standard for local anesthetics -rapid onset with intermediate duration of action -overdose marked by drowsiness, loss of consciousness and respiratory arrest |
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mepivacaine
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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 |
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bupivacaine
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-rapid onset and long duration of action
-significant vasodilatory properties |
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ropivacaine
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-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 |
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other drugs with local anesthetic effects
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antihistamine (diphenhydramine)
antidepressant (tricyclics) |
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drug interactions
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-antihistamines
-antiarrhythmics both synergystc -sulfonamide antibiotics -cholinesterase inhibitors |