Chapter 21: Local Anesthetics Flashcards
local anesthetics work by blocking ___channels to prevent transmission of painful stimulus
Na
voltage gated Na channels open when the membrane ___
depolarizes
t/f when the inactivation gate of the Na channel is close, the channel cannot be reopened
t
when the membrane re-polarizes, the inactivation gate ___ in preparation for next depolarization
relaxes
inactivation gates of na channels prevent prolonged ___
depolarization
why would it be dangerous to block all the Na channels?
not just found in neurons, also in skeletal muscle and cardiac muscle, so the heart and diaphragm wouldn’t contract and we would die
what is Tetrodotoxin? what does it do?
natural toxin found in puffer fish; blocks many na channels and can be fatal at low doses
what dose of tetrodotoxin is fatal in an adult human?
10-25mg
how can tetrodotoxin be used in research of cellular processes?
blocking Na channels makes it easier to observe other processes
t/f there is no therapeutic use for tetrodotoxin
t
local anesthetics block the Na channels of ___(small/large) diameter nerve fibers more effectively
small
the neurons that carry pain signals are ____ in diameter
small
small neurons like ____ can be the target of off-target effects of local anesthetics, but large neurons like ___ cannot
autonomic neurons; motor neurons
t/f if the concentration of local anesthetic is high enough, large diameter neurons can be blocked
t
the primary principle of local anesthetics is that they are administered to the local area where ____ is wanted
nerve block
local anesthetics allow for high ____ while having reduced risk of ___
drug concentration; systemic effects
the effect of local anesthetic is ___ as the effect is reduced as the drug diffuses away from the local site
transient
what is unique about epidurals and spinal blocks in terms of being local anesthetics
the anesthetic is not injected at the site that will feel pain, but rather to the area of the spinal cord that houses the nerves for that area
local anesthetics are relatively simple molecules that have what 3 parts?
lipophilic, hydrophilic, linker
local anesthetics are divided into 2 groups based on their linking groups: ___ and ___ type agents
ester and amide
cocaine is a ___ type local anesthetic
ester
procaine is___ local anesthetic that was developed based on discovery of cocaine as an anesthetic
prototypic ester
why are other agents used more frequently than procaine?
it has a short duration of action
Benzocaine is a ___type anesthetic that is administered by the ___ route
ester; topical
t/f benzocaine is used in many creams to treat sunburn pain
t
the ester bonds of benzocaine are cleaved by ___
esterases
esterases can ___ the duration of action of ester local anesthetics
shorten
lidocaine and bupivacaine are ___ type anesthetics
amide
amide anesthetics are used more often bc
they cant be craved by esterase’s, so have longer duration of action
___ is one of the common agents used in epidurals for childbirth
bupivacaine
compare the duration of action for lidocaine vs bupivacaine and what they are useful for
lidocaine has a moderate duration and useful in dental procedures; bupivacaine has longer duration and used in surgery and child birth
local anesthetic bind to what part of the Na channel?
inside of the pore
do local anesthetics pass through the Na channels?
NO
how do local anesthetics gain access to the inside of the Na channel w/o passing through the pore?
cross the cell membrane and access binding site from the inside
the ionized form of local anesthetics has a ___ affinity for the binding site
greater
t/f local anesthetics having lipophilic and hydrophilic parts help them cross the cell membranes to act on the channels
t
the hydrophilic parts of the local anesthetics have a ___ group that can be protonated depending on pH
tertiary nitrogen
when the pH and PKa are the same, there is a ____ split between charged and uncharged local anesthetics
50-50
the pka of lidocaine is 7.8, so at physiologic pH, there is a near ___ spilt of charged and uncharged drug
50/50
the ___ (charged / uncharged) form of local anesthetic is able to cross the membrane
uncharged
t/f bc the uncharged form of local anesthetic crosses through to the membrane so the equilibrium is thrown off
t
the effects of local anesthetics are stopped when the drug diffuses away from the Na channel which can then
return to resting closed state to await depolarization
t/f blood flow easily carries local anesthetic away from site of admisntration
t
the ADRs of local anesthetics are ___ dependent
dose
if local anesthetics get too much into systemic circulation, they can cause
respiration and cardiac arrest and death q
t/f repeated dosing of anesthetic is only given when necessary
t
how can the duration of action of a local anesthetic at its local site be prolonged w/o adding more anesthetic?
add a vasoconstrictor like epi prevents drug from flowing through local BV away from admin site
