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test 4 - Local Anesthetics
N/A
104
Pharmacology
Graduate
03/30/2010

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Term
What type of cells are voltage-gated sodium channels found in?
Definition
excitable cells - neurons, myocytes, cardiac cells
Term
What type of channel is essential for AP generation?
Definition
voltage-gated sodium channels
Term
Name two things that block voltage-gated sodium channels.
Definition
1) neurotoxins
2)local anesthetics
Term
sensation, emotion, thought, and movement all depend on _________ channels.
Definition
voltage-gated sodium channels
Term
What acts as the inactivation h-gate for voltage-gated sodium channels?
Definition
linker peptide between hexamers III and IV of the alpha subunit
Term
what forms the voltage-sensing m-gate for voltage-gated sodium channels?
Definition
S4 segment of each hexamer in the alpha subunit
Term
How many hexamers make up the alpha subunit of the v-gated sodium channel?
Definition
4
Term
Where do local anesthetics bind to the v-gated sodium channel?
Definition
in the carboxy terminus - between F1764 and Y1771
ALWAYS ACT ON HEXAMER IV AT S6 TRANSMEMBRANE SEGMENT OF THE ALPHA SUBUNIT
Term
sodium channels disorders in the brain can cause what two problems?
Definition
1) epilepsy.febrile seizures
2) myoclonic seizures
Term
primary erythermalgia can be caused by a disorder of ________ channels in peripheral nerves?
Definition
v-gated sodium channels
Term
what is the mechinism of tetrodotoxin and saxitonin?
Definition
pore-occlusion of v-gated sodium channels
Term
How do brevetoxins (from red tide) work?
Definition
persistent activation of v-gated sodium channels
Term
When v-gated sodium channels are in the resting state, the m-gate is _______ and the h-gate is _______.
Definition
closed, open
Term
When v-gated sodium channels are in the activated state, the m-gate is _______ and the h-gate is _______.
Definition
open, open
Term
When v-gated sodium channels are in the inactivated state, the m-gate is _______ and the h-gate is _______.
Definition
open, closed
Term
The _____ you use the v-gated sodium channels, the _______ the percentage of blocked channels in the presence of a local anesthetic/channel blocker.
Definition
more, greater

= "use-dependent block"
Term
What are the two theories for use-dependent block of local anesthetics?
Definition
1)Guarded receptor theory
2)Modulated receptor theory
Term
The guarded receptor theory proposes that the use-dependent block of local anesthetics is due to a change in ________
Definition
drug accessibility to receptor
Term
The modulated receptor theory states that use dependent block of v-gated sodium channels is due to a change in ________
Definition
receptor AFFINITY for the drug
Term
where are v-gated sodium channels found on nerves?
Definition
Nodes of Ranvier
Term
In order for local anesthetics to work, they must block ___________
Definition
3 successive nodes
Term
What are the two main types of pain fibers?
Definition
Adelta and C fibers
Term
What are C fibers responsible for carrying? (4)
Definition
1)SLOW pain
2)temp
3)mechanoreception
4)reflex responses
Term
What are Adelta fibers responsible for carrying? (3)
Definition
1)FAST pain
2)cold temp
3)touch
Term
Where do C fibers synapse?
Definition
substantia gelatinosa of the dorsal horn
Term
Where do Adelta fibers synpase?
Definition
rexed lamina I and dorsal horn
Term
Thicker fibers have ________ internodal distance than thin fibers.
Definition
greater
Term
What fibers are first blocked by local anesthetics and why?
Definition
B fibers because they are the thinnest
Term
what effect results from anesthetic action on B fibers?
Definition
vasodilation with associated hypotension (decrease in BP)
** OCCURS BEFORE PAIN BLOCKING TAKES EFFECT!
Term
What do B fibers carry?
Definition
autonomic preganglionics
Term
what is respionsible for the cardiotoxicity of local anesthetics?
Definition
the effect on potassium channels in the myocardium
Term
What channels do lidocaine and bupivacaine bind?
Definition
1)sodium
2)potassium
3)calcium

bind with lower affinity to K and Ca channels
Term
Name two drugs that increase the effect of bupivacaine.
Definition
nifedipine and nicardipine (L-type VGCC blockers)
Term
what is responsible for the de-esterification of local anesthetics with an ester link?
Definition
plasma pseudocholinesterases
Term
Name four local anesthetics that are esters.
Definition
procaine
tetracaine
benzocaine
cocaine
Term
what kind of link is found in procaine and tetracaine HCl?
Definition
ester link
Term
what type of link is found in lidocaine and bupivacaine?
Definition
amide link
Term
how are local anesthetics with amide links inactivated?
Definition
hydrolysis in hepatocytes by mixed function oxidase
Term
ester local anesthetics are ______ acting and amide local anesthetics are _______ acting.
Definition
short, long
Term
lidocaine, mepivacaine, bupivacaine, ropivacaine, and prilocaine are ______ local anesthetics
Definition
amide
Term
what does cocaine inhibit?
Definition
reuptake of catecholamines
Term
Cocaine enhances the action of ________
Definition
noradrenaline
Term
What is the ONLY local anesthetic that produces VASOCONSTRICTION?
Definition
Cocaine
Term
what is the potency of procaine?
Definition
1
Term
what is the potency of tetracaine?
Definition
16
Term
procaine interacts with what type of drugs?
Definition
antibacterial - sulfonamides
Term
what metabolic product of procaine is responsible for the inhibition of sulfonamides?
Definition
PABA
Term
What should be given with tetracaine in a spinal block and why?
Definition
10% dextrose - to increase the specific gravity
Term
Why do you need to incease the specific gravity when gicing tetracine in a spinal block?
Definition
To prevent the drug from traveling to the brain where it would block respiration

*need to tilt patients bed upright to prevent travel to brain
Term
what two ester anesthetics are for topical use only?
Definition
benzocaine and cocaine
Term
What can cocaine be used for?
Definition
topical use for eye
Term
what two amide anesthetics are long-acting and very potent so used for surgery?
Definition
Bupivacaine
Ropivacaine
Term
what amide anesthetics are used topically?
Definition
prilocaine and lidocaine
Term
what amide anesthetic is used for an epidural in labor?
Definition
Bupivacaine
Term
what are the modes of administration for procaine?
Definition
nerve block
infiltration
spinal
Term
what does it mean if a drug is administered by infiltration?
Definition
it is injected into tissue but no specific nerve is targeted
Term
What is a nerve block?
Definition
inject drug into tissue while targeting a specific area
* usually only done in lower body
Term
Where are nerve blocks given?
Definition
lower body
*try to avoid upper body because of important structures such as the diaphragm (would paralyze breathing)
Term
Where are drugs injected when administered via epidural?
Definition
DRG
Term
In what mode of local anesthetic administration does the drug remain localized?
Definition
epidural administration - remains in the DRG allowing for lower dosing
Term
Where are drugs injected in a spinal block?
Definition
into the CSF surrounding the spinal cord
Term
What do you have to worry about if topical or infiltrative anesthetics are applied in high concentration over large areas?
Definition
systemic toxicity
Term
What are topical anesthetics ineffective on?
Definition
INTACT skin
Term
What is Lidocaine used topically for?
Definition
Herpes zoster blisters
Term
What is EMLA?
Definition
eutectic mixture of local anesthetics
lidocaine +prilocaine for venepuncture
Term
What three local anesthetics can be injected into tissue around incision for minor operation (via infiltration)?
Definition
lidocaine
procaine (short-acting)
bupivacaine (long-acting)
Term
what is given in addition to local anesthetics (lidocaine/procaine/bupivacaine) in order to offset their effect of vasodilation?
Definition
epinephrine - vasoconstriction
Term
Where should epinephrine not be used with local anesthetics for minor surgery and why?
Definition
fingers, toes, ears, nose, penis
*they are end-artery supplied so EPI could cause gangrene
Term
Would could be a side effect of administering lidocaine + EPI via infiltration for finger surgery?
Definition
gangrene/ necrosis coould occur - SHOULD NOT USE EPI
Term
When using IV regional anesthesia, how long should you wait before releasing the pressure cuff and why?
Definition
20 min - to prevent systemic toxicity
Term
Intravenous regional anesthesia is used for ______ surgery?
Definition
limb
Term
In IV regional anesthesia, the drug should be injected ______ to pressure cuff
Definition
distal
Term
Why is the injected IV distal to the pressure cuff in IV regional anesthesia
Definition
to arrest blood flow
Term
what two drugs can be used in IV regional anesthesia?
Definition
lidocaine
prilocaine
Term
what are the adverse effects of a nerve block?
Definition
1)onset of anesthesia is slower
2)need high accuracy of injection
Term
what is a good mode of anesthesia administration for an episiotomy?
Definition
pudendal nerve block
Term
nerve block are good for what type of procedures?
Definition
surgical and dental - injected near specific peripheral nerves
Term
what are spinal blocks used for?
Definition
surgery of abdomen, pelvis, leg
obstetrics
Term
what two drugs are used for spinal blocks?
Definition
tetracaine
lidocaine
Term
drugs given in a spinal block act on ______ and _______
Definition
spinal cord
spinal roots
Term
When giving a spinal block of tetracaine or lidocaine, how do you minimize cranial spread?
Definition
elevate head and use 10% dextrose to make it heavier that CSF
Term
What are the adverse effects of a spinal block?
Definition
1)bradycardia.hypotension - symp. block
2)respiratory depression - phrenic n. or resp center block
3)urinary retention - pelvic parasymp. block
Term
drugs injected into peridurral space act on _______ and _______
Definition
nerve roots and spinal roots
Term
what two drugs can be administered via epidural?
Definition
lidocaine
bupivacaine
Term
what can epidural administration of local anesthetics be used for?
Definition
surgery of abdomen, pelvis, leg
obstetrics (painless birth)

*same as spinal block
Term
why are adverse effects lees likely with epidural than with spinal?
Definition
because cranial spread is limited in epidural - drug stays in DRG

*still see urinary retention with epidural
Term
what are the adverse effects common to all local anesthetics?
Definition
1)resp depression, coma, death
2)decreased myocardial excitability, conduction rate, contraction force
3)profound hypotension (due to vasodilation)
Term
neurotxocity occurs at _______ doses than cardiotoxicity when using local anesthetics.
Definition
lower
Term
What is the CC:CNS ratio?
Definition
used for local anesthetics to describe the dose causing cardiovascular collapse/dose causing CNS collapse
Term
If a local anesthetic has a CC:CNS ratio of 10 and it causes seizures at 5 mg/kg than at what dose with it cause cardiac arrest?
Definition
50mg/kg
Term
The first sign of local anesthetic neurotoxicity is _________
Definition
excessive talkativeness or total silence
Term
what are the signs seen in neurotoxicity?
Definition
change in thought processes
perioral parasthesias
whole body flushing feeling
tinnitus
generalized seizures
Term
what part of the limbic system is involved with convulsions seen in neurotoxicity of local anesthetics?
Definition
amygdala nucleus
Term
coma, resp and cardiac arrest are found in what phase of neurotoxicity?
Definition
depression phase
Term
what is seen in the excitation phase or neurotoxicity?
Definition
tinnitus
numbness
nystagmus
dizziness
restlessness
tremor
convulsions
Term
what is important to do while administering local anesthesia?
Definition
keep the patient talking!!
Term
What is Logorhhea?
Definition
constant flow of words - may or may not make sense
*can be the 1st sign of local anesthetic neurotoxicity
Term
what are the effects of cardiotoxicity due to local anesthetics?
Definition
hypotension
decreased myocardial contractility
bradycardia w/ long PR interval
widened QRS
increased Q-T
dysrhytmias
Term
how do local anesthetics cause decreased myocardial contractility?
Definition
inhibit calcium channels
Term
cardiotxocity of local anesthetics involves a ____________ in refractory perios,firing threshold, and conduction time
Definition
increase
Term
what is the hematologic side effect of prilocaine, lidocaine, and benzocaine?
Definition
methemoglobin
Term
what metabolite of prilocaine is resonpsible for the oxidation of Hb to MetHb?
Definition
O-toluidine - liver metabolite of prilocaine
Term
what is O-toluidine?
Definition
liver metabolite of prilocaine - oxidizes Hb
Term
what are the efefcts of MetHb?
Definition
*cyanosis
dyspnea
dizziness/syncope
gray cutaneous discoloration
tachypnea
fatigue
weakness
exercise intolerance
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