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79 Cards in this Set

  • Front
  • Back
LAs reversibly block the _____ and _____ of nerve impulses
generation and propagation
bi-directional blockade
LAs can alter both sensory and motor function because LAs can block function in ALL excitable cells
LAs used to decrease what?
1) pain
2) temp
3) touch perception
4) skeletal muscle tone
level of effect depends on what?
1) agent used
2) route of administration
3) drug concentration at site
4) lipophilicity
route of LAs
1) topical (skin, MM)
2) parentetral (peripheral, cnetral, spinal)
3) rectal
4) ophthalmical
many of LAs also used as:
antiarrhythmics
What control the compounds ability to penetrate the nerve sheath and enter the nerve membrane?
the lipophilicity of the aromatic group
most of LAs are:
ionizable weak bases
ionizable weak bases can exist as:
1) the freebase or
2) the positively charged form
which will alter their action at the site
all agents act to decrease:
the permeability of the membrane to sodium ions
LAs bind to sites in the:
Na channel of the voltage gated Na channels (inhibit Na inflow during depolarization)
low concentration of LAs decreases:
both 1) the rate of rise and
2) the height of the action potential
(higher conc. can abolish it totally)
LAs increase:
1) firing threshold
2) total propagation time
in myelinated fibers, this occurs only at the:
Nodes of Ranvier
K outflow
may also be inhibited somewhat, but not nearly to the extent of Na
most of LAs act by binding to:
inner portion of Na channel
Which nerves are affected first?
1)small diameter nerves
2) more rapidly stimulated fibers
3) autonomic fibers
Why are small diameter nerves affected first?
small diameter nerves are affected first, then larger diameter nerves due to the # of channels to be blocked (greater in large fibers)
Why are more rapidly stimulated fibers blocked first?
due to 1) more frequent opening of Na channels and
2) the ability of the LAs to get into channel to bind
the order of fibers get affected
1st: autonomic fibers
2nd: sensory
3rd: motor
selsective Na channel blockers
1) tetrodotoxin
2) saxitoxin
tetrodotoxin
from pufferfish
saxitoxin
from red tide microorganisms (paralytic shellfish poisoning)
Where selective Na channel blockers block?
OUTER mouth of Na channel
LAs use as antiarrhythmic agents is due to the:
1) blockade of Na channels in myocardial tissues
2) effective decrease in firing rate
3) effective decrease in passage of signals through conductive fibers
topical
decrease pain of wound, burn, MMs
infiltration
injected around area (ie. for Sx)
regional nerve block
injected close to nerve that innervates the area to be anesthetized
spinal
injected into lumbar subarachnoid space to get to nerves in that area going to various body sites)
epidural
given under the dura mater - keeps agent from rising higher up spinal column)
intravenous
usually for Sx on a specific limb
selection of LAs minly based on its:
pharmacokinetics
fast onset
1) lidocaine
2) prilocaine
slow onset
1) procaine
2) tetracaine
short duration (15-30 min.)
1) procaine
2) chloroprocaine
intermediate duration (30-90 min.)
1) lidocaine
2) prilocaine
long duration (2-3 hrs)
tetracaine
epi.
may be used to increase duration, but is not always effective
onset on MMs
fastest onset: benzocaine
2nd: lidocaine and cocaine
(topical duration: 30-60 min.)
local hypersensitivity more commone with:
ester type
examples of preps which increase sensitivity risk:
1) tartrazine
2) sulfites
systemic absorption can lead to:
1) cardiotoxic risk
2) potential CNS symptoms (sedation, dizziness, disorientation, tremors, seizures, resp. arrest)
the LAs are classified by:
their structure
1) ester
2) amide
3) neither
esters
1) benzocaine (oragel)
2) procaine (novocaine)
3) chloroprocaine (nesacaine)
4) tetracaine (pontocaine)
5) cocaine
6) cetacaine (cetylite)
amides
1) lidocaine (xylocaine)
2) prilocaine (citanest)
3) mepivacaine (carbocaine)
4) bupivacaine (marcaine)
5) articaine (septocaine)
6) ropivacaine (naropin)
not true amides or esters
pramoxine (proctofoam)
esters are hydrolyzed by:
cholinesterases
1) Benzocaine (Oragel)
1) poorly water soluble
2) topical use only
3) pKa ~3.5
excessive absorption of Benzocaine may lead to:
methemoglobinemia
2) Procaine (Novocaine)
1) 1st synthetic local anesthetic
2) slower onset with short duration
3) weak potency
4) fairly low systemic toxicity
5) use superceded by better agents (amides)
Procaine is best for:
infiltration and nerve block
3) Chloroprocaine (Nesacaine)
1) ester
2) rapid onset, short duration
3) low syst. toxicity
4) used in high [ ]
5) for infiltration, nerve block, IV, and epidural use
4) Tetracaine (Pontocaine)
1) ester
2) long duration with slow onset
3) spinal (major use)
4) topical (absorption across MMs limit its use)
potency of Tetracaine
10 times more potent than procaine, but also 10 times more toxic
Why Tetracaine used in spinal anesthesia?
because the barriers decrease diffusion and decrease toxicity risk
5) Cocaine
1) ester
2) C-2 controlled substance
3) only use in topical on MMs(too toxic for other uses)
uniquness of Cocaine
1) potent vasoconstrictive activity
2) addiction liability in addition to it's LA effect
6) Cetacaine (Cetylite)
1) ester
2) topical for local skin disorders (not for MMs)
3) for opthalmology
Cetacaine is a mixture of:
1) Benzocaine
2) Tetracaine
3) Butyl Aminobenzoate
use of Cetacaine
1) topically
2) rectally
3) spray to inhibit the gag reflex (during bronc. exam)
amides are metabolized mainly in the:
liver
1) Lidocaine (Xylocaine)
1) amide
2) most commonly used LA
3) rapid onset with intermediate duration
4) used for most types of applications
Why many formulations of Lidocaine include Epi?
because Lidocaine causes vasodilation
2) Prilocaine (Citanest)
1) amide
2) similar to lidocaine in properties, but LESS vasodilation
3) rapid onset, intermediate duration
toxicity of Prilocaine
least toxic of the amides, but can still cause methemoglobinemia
3) Mepivacaine (Carbocaine)
1) amide
2) similar to lidocaine
3) used for infiltration, nerve blocks, epidural
4) not effectively topically
Why Mepivacaine is not used in obstetrics?
because biotransformation in fetus is prolonged
4) Bupivacaine (Marcaine)
1) amide
2) long duration, with slower onset
3) high potency
4) used for infiltration nerve block, epidural, and spinal
Is Bupivacaine more toxic than Lidocaine?
Yes! (cardiotoxic)
5) Articaine (Septocaine)
1) amide
2) only available in US in combination with Epi
3) similar to lidocaine
4) short duration and rapid onset
use of Articaine
used for dental and peridontal procedures
toxicity of Articaine
low systemic toxicity due to rapid breakdown (it has an ester group in addition to an amide)
6) Ropivacaine (Naropin)
1) amide
2) long duration
3) similar to Bupivacaine, but less cardiotoxic
4) less lipid soluble, and more rapidly metabolized than Bupivacaine
use of Ropivacaine
similar to Bupivacaine
1) infiltration
2) nerve block
3) epidural
4) spinal
Bupivacaine and Ropivacaine
1) Bupivacaine: R-isomer
2) Ropivacaine: S-isomer
Pramoxine (Proctofoam)
1) not true amide or ester
2) topical agent for relief of hemorrhoids, rectal pain and itching of skin disorders (pruritis)
potency of Pramoxine
weak potency (will not totally abolish gag reflex)
Pramoxin mixed in combination with many products such as:
1) hydrocortisone
2) calamine
liposomal formulation
Liposomes are somewhat like cells in that they are round shells of phospholipids, the basic components of human cell walls. Enclosing a drug within a liposome entraps the drug as ‘payload,’ protecting it from early degradation within the body. Liposome encapsulation also improves a medication’s bioavailability (the amount of time and specific distribution within the body), which can extend the treatment effect and reduce dosing.