Exam5- Local Anesthetics Flashcards
local anesthetics vs analgesic drugs
analgesic= specifically inhibit nociceptive pathway local= non-secific inhibitors of neuronal conduction
afferent nociceptors
=Adelta and C fibers
-conduct thermal , intense mechanical, and chemical stimulation to a second order neuron or brain
Local Anesthetic Mechanism of Action
block voltage gated Na+ channels on nerve membranes
=stops generation and conduction of action potentials
locals will more readily reach their sites of action when they are in ___ form
LIPID SOLUBULE (UNCHARGED)
all locals are strong/weak acids/bases?
WEAK BASES
pH of all locals are between ___ and ____
7.5 and 9.5
physiological pH =
7.4
most of the drug will begin it its protonated/non protonated form
protonated
drug pH = 7.5 - 9.5
physiological pH = 7.4
pKa = pH at___
equilibrium of BH+ and B
when pH= 7.4 base is protonated/nonprotonated
BH+
when pH>pKa there is more ___
B
lidocaine has a pKa of
7.9
the closer pKa is to physiological pH the ____ the onset of the drug.
faster
fiber diameter/myelination affects___
susceptibility to local anesthetic
- larger nerves are less susceptible to block than smaller nerves
- myelinated nerves are less susceptible than non-myelinated n.
firing frequency and susceptibility to locals
locals bind active channels more readily than resting channel
position of fiber affects its susceptibility to locals….
superficial fibers are more easily reached ∴ more susceptible
pain and temperature neuron fiber type
delta
pain and temp neuron diameter
2-5um ∴ easy to target
order of nerve function loss:
sympathetic pain cold warm touch motor
critical length hypothesis
in order to be effective the field of action of a local anesthetic must include at least 3 nodes of Ranvier
axon size and number of nodes ranvier
larger axons= less nodes
small axons= more nodes
∴smaller axons are more susceptible to locals bc there are more nodes within a given nerve block field
amide locals list
lidocaine mepivacaine prilocaine bupivacaine articaine ropivacaine
ester locals list
cocaine procaine tetracaine benzocaine proparacaine
amides or esters are metabolized in blood
esters
-readily hydorlyzed by esterases in blood into PABA
PABA= common allergy
amide metabolism
cytochrome p450 in liver
∴ have a longer duration of action than esters
-cause less allergic reactions than esters
ester vs amide pKa
esters usually have a higher pKa
∴ slower onset and shorter duration
amides with short duration of action
prilocaine and lidocaine
amides with intermediate duration of action
mepivacaine
articaine
amides with long duration of action
ropivacaine
three routes of local administration
- topical
- infiltration/nerve block
- epidural/spinal
____ are commonly used for topical applicaiton
binzocaine
tetracaine
___ are commonly used for infiltration
licocaine mepivacaine prilocaine articaine bupivacaine (all amides)
all locals except cocaine are vaso____
dilators
locals that are the least vasodilators
mepivacaine
prilocaine
∴ don’t need to be delivered with a vasoconstrictor
vasoconstrictors benefits
- prolong the duration of anesthesia by preventing diffusion from the site of action
- limit systemic toxicity of local anesthetics
- reduce blood loss for surgical procedures
epinephrine hydorcholide
most common with local injection
only targets alpha-1 receptors
levonordefrin hydrochloride
less common
selective alpha-1 receptor agonists
alpha-1 agonists should be used with caution w/___
patients with cardiovascular disease
because they cause hypertension
**ALWAYS avoid delivery into systemic circulation and only administer via infiltration when necessary at the lowest dose possible
locals and MAO oxidase inhibitors
-can increase the effects potentially resulting in a hypertensive crisis
lidocaine
=most commonly used local anesthetic
- common prep= 2% lidocaine hydrochloride with 1:100,000 epinephrine
- safe for kids
- inexpensive
articaine properties
similar to lidocaine
bupivacaine properties
prolonge duration of action
mepivacaine properties
very little vasodilation
doesn’t require a vasoconstrictor
prilocaine properties
doesn’t require a vasoconstrictor
benzocaind
=ester used in dentistry
-used topically as a numbing agent
(no longer via infiltration)
one cartridge=___ ml
1.8ml
2% =___ mg/ml
=___ mg/cartridge
20mg/ml
=36mg/cartridge
1:10000 epi=___ ug/ml
=___ug/cartridge
10ug/ml
=18ug per cartridge
EMLA
Eutectic mixture of local anesthetics
=2.5%prilocaine and 2.5% lidocaine
-for pain and itching
LMX-4
=liposomal formulation of 4% lidocaine
-for pain and itching
topical locals for pain and itching
EMLA
LMX-4
tetracaine
benzocaine
ophthalmology locals
proparacaine
-for ocular proceudres
repeated administration=corneal damage/blindness
locals for minor lacerations
=topical analgesics with epinephrine
TAC= tetracaine, adrenalin/epi, cocaine
LET= lidocaine, epinephrine, tetracaine
locals for surgical wounds
pre-surgical infilatration
locals for major lacerations
pack with agents soaked with TAC or LET
digital injury locals
DO NOT USES EPINEPHRINE you can use digits form ischemia!!!!
induced nerve block
administered into space around spinal column, below L1
- epidural space = epidural block
- subarachnoid space =spinal block
- paravertebral region= paravertebral block (more diffuse)
epidural anesthesia
- between L3 and L4 through ligament flavor
- most commonly ropivacaine
- bupivacaine is also used but is more cardiotoxic (arrhythmias)
systemic toxicity of local anesthetic
CNS: excitation initially then severe toxicity = seizures
Cardiovascular: decreased conduction, arrhythmias
hypotension, reduced autonomic activity
Hemoblobin: prilocaine is metabolized in the liver and then converts hemoglobin to methemoglobin
PABA
paraaminobenzoic acid
=metabolite of ESTER anesthetics
