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24 Cards in this Set
- Front
- Back
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Where is the MOA of Local Anesthetics?
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Blockade of Voltage gated Na+ channels---so blocks all APs and all neuronal conduction
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Where are local anesthetic binding sites located?
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INTRAcellulary
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What are the 2 steps for local anesthetic action?
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1. Passive diffusion across cell membrane to inside cell
2. binding to specific binding site of Na+ channel |
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What form of local anesthetic is required to pass the cell membrane and enter the cell?
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UNCHARGED form
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What form of local anesthetic is required to bind to the Na+ channel?
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Charged form
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Role of Hydrophobic group (Aromatic) of Local Anesthetic?
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Lipophilicity---increases local tissue binding, potency and duration of action
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Role of Hydrophilic Group (Amine) of Local Anesthetic?
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site of action of the L.A.
(remember uncharged-penetrates & charged-binds) |
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What determines the speed on onset of Local Anesthetics?
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pKa----determines amount of charge at the physiological pH.
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low pKa : ________charge: ___________ cell entry
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less charge ----- rapid cell entry
Lidocaine = 7.9; Procaine= 8.9 |
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What determines the potency of Local Anesthetics?
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Hydrophobic group (lipid solubility of it)
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What determines the speed of onset of Local Anesthetics based on the pKa?
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Hydrophilic Group (Amines)
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What determines the duration of action of a Local Anesthetic?
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Ester vs. Amide linkage
Ester= hydrolysed (liver, serum) Amide= stable |
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What structure of L.A. is primarily hepatic, accumulates, and toxicity is dose related?
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Amides
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What structure of L.A. is hydrolyzed in the plasma by pseudocholinesterases, no accumulation, and toxicty can occur via injxn or persistent exposure?
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Esters
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How do determine whether a local anesthetic has an Ester vs. Amide linkage?
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ALL Amides have an i before the -caine.
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What pain fiber is small and unmyelinated?
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C-fibers
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What pain fiber is small and myelinated?
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Adelta fibers
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Where are pain fibers blocked by L.A.?
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Lower
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What carries position sense via large, myelinated fibers?
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Aa & Ab fibers
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Where are motor and propioceptive (position) blocked by L.A.?
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Higher
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What is an example of a vasoconstrictor that lengthens anesthesia by slowing local removal and slows blood loss?
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Cocaine
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Synthetic L.A. do NOT have _________________ activity.
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instrinsic vasoconstrictor activity
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What is the benefit to using synthetic local anesthetics?
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lowers systemic concentrations---ex. epi
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Which fires at a faster rate, has a longer AP duration, but has poor passive propagation to overcome the partial block? Sensory or Motor?
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Sensory
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