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Gen Exam 3 + Final > Basic Pharmacology of LAs > Flashcards

Basic Pharmacology of LAs Flashcards

(63 cards)

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1
Q

LAs are ___ molecules

A

amphipathic

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2
Q

T/F
LAs bind exclusively to Na channels and plasma proteins

A

False
primarily to Na channels
but also K, Ca, & G-protein-coupled receptors

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3
Q

🔷
What determines…
onset
potency
duration

A

onset = pka
potency = lipid solubility
duration = protein binding

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4
Q

⭐️
T/F
LAs suppress action potentials in excitable tissues by blocking ligand-gated Na+ channels.

A

False
voltage gated

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5
Q

LAs block pain impulse transmission by inhibiting action potentials in ___ fibers

A

nociceptive

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6
Q

Four groups of myelinated A fibers

A

Aa: skeletal muscle
Ab: tactile sensation
Ag: muscle spindles
Ad: nociception & cold

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7
Q

Unmylinated C

A

dull pain from skin and viscera

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8
Q

Myelinated B

A

autonomic preganglionic
slower

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9
Q

Where are voltage-gated Na channels found?

A

nerves
myocardium

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10
Q

Which fibers are affected by Surgical incision or trauma

A

free nerve endings of Ad
(skin, muscle, joints, bone and viscera)

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11
Q

Voltage-gated Na channel
structure

A

pore-forming alpha subunit
-one or two b subunits.

alpha subunit:
four domains (I-IV) each w/ six segments (S1-S6) that wrap round a bell-shaped central channel

channel is formed by:
S5 & S6 segments + short loops of amino acids linking them

inactivation gate:
loop connecting domains III & IV

S4 in each domain:
+ charged arginine or lysine amino acids
voltage-sensitive region of the Na+ channel.

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12
Q

voltage-sensitive region of the Na+ channel.

A

S4

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13
Q

Resting-state:
MP
generated by…

A

-70 mv
K+ out (along their gradient)
anions stay inside (mostly proteins)

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14
Q

inactivation gate location

A

between domains III and IV

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15
Q

S4 segment activity

A

resting state:
S4 in “down” position
makes it nonconductive

depolarization:
outward spiraling opens Na channel
exposes inactivation gate

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16
Q

🔷
The ionized form binds to ___ voltage-
gated Na+ channels in a reversible and concentration-dependent manner.

A

open

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17
Q

binding site for local anesthetics

A

domain IV, loop S6
only accessible when the channel is open

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18
Q

use-dependent or phasic block

A

binding of LA to open Na+ channels increases with the frequency of nerve depolarization

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19
Q

(MoA)
Dose dependent effects of LAs

A

increased LA [ ]:
↓ peak action potential
↑ firing threshold
↓ impulse conduction
↑ refractory period

↓ all nerve conduction

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20
Q

Why does Bupivicaine cause more cardiac effects than Lidocaine?

A

bupivacaine:
higher affinity & slower dissociation
↓
accumulates in diastole
↓
prolong conduction
↓
re-entry-induced arrhythmias

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21
Q

(para/sympathetic) fibers are most easily blocked & require lowest LA [ ].

A

sympathetic

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22
Q

Usually reaches higher dermatome

A

sympathetic block

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23
Q

LAs are ___ soluble salts of lipid-soluble ___

A

water
alkaloids

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24
Q

How can LA structure be changed to increase lipid solubility, potency & duration of action

A

increasing the length of carbon chains attached to either the aromatic ring, amide linkage, or the tertiary amine

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25
Replacement of the tertiary amine by a piperidine ring
↑ lipid solubility and duration of action
26
butyl group in place of the amine on the benzene ring of procaine gives
tetracaine
27
addition of a propyl or butyl group to the amine end of mepivacaine results in
ropivacaine or bupivacaine, respectively
28
Bupivacaine enantiomers
dextro-enantiomer: selectively blocks 🩷 Na channels bad so we started using 2 different Levo-enantiomers levobupivacaine & ropivacaine (less effect on 🩷 conduction & contractility)
29
pKa
pH at which the ionized and unionized forms are present in equal amounts
30
LAs are (acids/bases) so a higher pka means (more/less) inonization
bases more
31
high protein binding to ___ have a longer duration of action and lower bioavailability.
a1-acid glycoprotein
32
decreases protein binding & thus and increases the risk of toxicity (3)
Hypoxia, hypercarbia, and acidaemia
33
vasoactivity of local anaesthetics influences (2)
potency duration
34
Levobupivacaine and ropivacaine bimodal vasoactivity
vasodilate at clinical doses vasoconstrict at subclinical doses
35
Routes of administration
topical (skin and airway) subcutaneous intravenous perineural epidural intrathecal
36
peak plasma concentration after a single dose
intrapleural > intercostal > lumbar epidural >brachial plexus > subcutaneous > sciatic > femoral. M&M: intravenous (or intraarterial) > tracheal > intercostal > paracervical > epidural > brachial plexus > sciatic > subcutaneous
37
Which are less protein bound? esters or amides
esters (lower protein binding = shorter duration)
38
Tissue distribution tends to be proportional to (3)
LA's tissue/blood partition coefficient tissue mass tissue perfusion
39
We're concerned about PABA with (ester/amide) LAs
ester
40
(ester/amide) LAs are more prone to accumulation with hepatic dysfunction or reduced hepatic blood flow
Amide they are metabolized by the liver and have slower metab than esters (esters = rapid hydrolysis by plasma esterases!)
41
undergoes metabolism in the lungs
Prilocaine
42
An allergy to an amide LA is most likely due to...
an additive such as the stabilizing agent methylparaben or response to vasopressors mistakenly seen as allergy
43
has a high hepatic extraction ratio: clearance depends on hepatic blood flow & ~unaltered by changes in hepatic enzyme activity
Lidocaine
44
LA Adjuvants
adrenaline clonidine opioids ketamine dexamethasone dexmedetomidine midazolam
45
eutectic
mixing 2 compounds to produce a substance that has 1 set of physical characteristics
46
eutectic mixture of local anaesthetic (EMLA)
crystalline bases of 2.5% lidocaine and 2.5% prilocaine in an oil/water emulsion ↓ melting point than separately can use higher [ ]
47
rate and degree of diffusion across the placenta depends on
protein binding pKa maternal & fetal pH
48
Considerations for LAs in prolonged labour
acidosis in the fetus ↓ ion trapping ↓ accumulation in the fetus
49
(Amide/ester) LAs do not cross the placenta in significant amounts
Ester d/t rapid hydrolysis
50
T/F Local anesthetics cause both systemic AND local toxicity.
True
51
lower systemic toxicity among the amides
Ropivacaine and levobupivacaine lower affinity for 🩷 channels
52
T/F majority of perioperative nerve injuries are unrelated to regional anaesthesia
True
53
methaemoglobinaemia shifts the OxyHgb curve
left ↓ ability of Hgb to release oxygen to tissues
54
LAs that can cause methemoglobinemia
prilocaine Benzocaine lidocaine
55
Intra-articular local anaesthetics risks
chondrotoxicity (esp w/ osteoarthritis)
56
LAs anti-inflammatory effects MoA
↓ polymorphonuclear leukocyte adherence, migration & accumulation at site alters macrophage and monocyte function
57
LAs anti-inflammatory effects cons
~↑risk bacterial infxn
58
Possible antimetastatic properties
Surgery ↓ antitumour cell activity ↑ protumor activity LA may ↓ cancer recurrence: -attenuation this stress response -direct anti-tumor effect not proven
59
lidocaine for neuropathic pain MoA
unexplained by only blockade of voltage gated Na channels reduction of spontaneous pain, allodynia, & hyperalgesia
60
Catheter for continuous or repeated administration of local anesthetic risks
leakage, migration, infection
61
Phentolamine mesylate
non-selective alpha-adrenergic antagonist vasodilates halve the reversal time of LA
62
T/F All local anesthetics target the voltage-gated Na channel
True
63
T/F Only certain LAs carry risk of toxicity.
False All have toxicity risk

Gen Exam 3 + Final (13 decks)

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