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Summer '14 Pharm III > Locals > Flashcards

Locals Flashcards

1
Q

Procaine onset and pKa

A

Slow

8.9- 3% unionized

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2
Q

Tetracaine onset and pKa

A

Slow

8.5- 7% unionized

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3
Q

Bupivacaine onset and pKa

A

Moderate

8.1- 17% unionized

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4
Q

Chloroprocaine onset and pKa

A

Fast

8.7- 2% unionized (Given in high concentration, thus fast onset)

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5
Q

Lidocaine onset and pKa

A

Fast

7.9- 24% unionized

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6
Q

Etidocaine onset and pKa

A

Fast

7.7- 33% unionized

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7
Q

Mepivacaine onset and pKa

A

Fast

7.6- 39% unionized

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8
Q

Afferent cell bodies are contained in the

A

Dorsal root ganglia

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9
Q

Efferent cell bodies are contained in the

A

Ventral root ganglia

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10
Q

In a nerve, a larger diameter results in slower/faster conduction velocity?

A

Faster

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11
Q

Describe A fibers

A

Myelinated, 1-22 microns. Alpha, beta, gamma, delta subtypes (Largest to smallest in that order)

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12
Q

Describe B fibers

A

Myelinated, 1-3 microns

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13
Q

Describe C fibers

A

Unmyelinated, 0.1-0.25 microns

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14
Q

A-alpha fibers

A

Motor, proprioception

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15
Q

A-beta fibers

A

Motor, touch, pressure

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16
Q

A-gamma fibers

A

Motor/muscle tone (muscle spindles)

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17
Q

A-delta fibers

A

Pain, temperature, touch (we care about these ones in particular)

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18
Q

B fibers

A

PREganglionic autonomic

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19
Q

C fibers

A

Dull pain, temperature, touch, POSTganglionic autonomic.

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20
Q

FIber conduction velocity fastest to slowest

A

A-a A-b A-g A-d B C

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21
Q

Do large fibers have a high or low threshold for excitability

A

Low

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22
Q

Do larger fibers tend to get more or less exposure to LA

A

Less, the bigger fibers are typically inside of the nerve bundle. The smaller, outer fibers tend to get more LA and are thus easier to block.

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23
Q

Differential block- what do we see clinically? How does this differ with lab experiments?

A

Clinically, sensitivity is inversely related to size, thus we see autonomic block, sensory block, and then motor block.

In the lab, the larger fibers are actually more sensitive when isolated.

May be due to- larger nerves inside of nerve bundle, variations in nerve activity, variable ion channel mechanisms.

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24
Q

What is more important in determining onset sequence and recovery in a mixed peripheral nerve?

A

Location! Much more important than inherent sensitivity.

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25
Q

Outer surface of a nerve is the _____ and it serves _____

Inner surface of a nerve is the _____ and it serves ______

A

Mantle, proximal structures

Core, distal structures

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26
Q

Typical sequence of blockade

A

Sympathetic (vasodilation, warm skin. feel feet to check uneven block.)

Loss of pain and temperature sensation

Loss of proprioception

Loss of touch and pressure

Motor block

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27
Q

RMP is approximately _____ and it largely determined by __

A

-70 to -90 millivolts

K+

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28
Q

Action potential

A

Rapid depolarization of the membrane lasting 1-2 milliseconds

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29
Q

Nerve stimuli include

A

mechanical, thermal, chemical, and pressure stimuli

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30
Q

____ is responsible for depolarization and changes the membrane potential to _____

A

Na+ influx

+20 to +40 millivolts

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31
Q

How do LAs block nerve conduction

A

Inhibition of the influx of Na+ ions by blocking sodium channels (more likely when channels are in the inactivated state)

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32
Q

In a completely resting nerve, what determines sensitivity?

A

Lipid solubility of the LA, as the drug cannot easily access closed sodium channels. More active nerves are more easily blocked (at least in theory)

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33
Q

LAs easily access ______ Na+ channels and

easily bind to _______ Na+ channels

A

activated-open

inactivated-closed

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34
Q

How are LAs chemically classified

A

A lipophilic head (aromatic ring) and either:

Amide (NH) chain or

Ester (COO-) chain and

a hydrophilic tail (tertiary amine)

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35
Q

Amides

A

Two “i’s” in the drug name. LIdocaIne, bupIvacaIne.

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36
Q

Esthers

A

One “i” in the drug name. Cocaine.

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37
Q

Esther biotransformation

A

Hydrolyzed by nonspecific esterases in plasma and tissues (mostly liver). Cocaine is an exception.

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38
Q

Amide biotransformation

A

Metabolized in the liver

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39
Q

The more lipid soluble a LA is the more/less potent it is and the longer/shorter its duration is compared to water soluble LAs

A

More potent

Longer duration

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40
Q

A longer intermediate chain leads to

A

Increased potency and toxicity

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41
Q

Longer terminal groups on the tail and aromatic ring lead to

A

Increased potency and toxicity

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42
Q

T/F

Enantiomers of chiral LAs differ in kinetics, dynamics, and toxicity.

A

True

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43
Q

The distance between nodes of ranvier contribute to

A

Differential block

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44
Q

Internodal distance ______ with fiber diameter

A

Increases

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45
Q

An impulse can still make it through how many blocked nodes

A

2, blockade of 3 nodes will eliminate conduction

46
Q

Differential block can be described as

A

Sensory block with incomplete motor block

A-delta and C fibers blocked, while A-a, b, g, fibers are not completely blocked

47
Q

In a differential block, pts will still be able to feel what with surgical stimulation

A

Pressure

48
Q

First LA to demonstrate a differential block

A

Bupivacaine

49
Q

LA systemic absorption is governed by

A

physiochemistry (pKa, pH, lipid solubility), physiological conditions at site(pH, pCO2, temperature, pt characteristics), volume of solution, additives (epi), and concentration of the drug

50
Q

Absorption by block type, high to low

A 
IV
Trach
Intercostal
Caudal
Paracervical
Epidural
Brachial plexus
Subarachnoid
SubQ
51
Q

Which form of the LA is able to cross the nerve sheath and membrane

A

Unionized form

52
Q

As unionized LA diffuses across the nerve membrane what happens to the remain drug

A

Ionized and unionized re-equilibrate–> more unionized available to cross membrane

53
Q

Ionized drug forms are favored when

A

An acidic drug is in a basic environment

A basic drug is in an acidic environment

54
Q

Unionized drug forms are favored when

A

An acidic drug is in an acidic environment

A basic drug is in a basic environment

55
Q

All LAs are basic/acidic drugs?

A

All are weak bases, though they come packaged in acidic environments

56
Q

What is pKa

A

The pH at which 50% of a drug is ionized and 50% is unionized

57
Q

What would be the ideal pKa for a LA

A

7.4 (body pH) Nonionized to penetrate nerve, ionized to block sodium channels

58
Q

What determines the proportion of the LA in the nonionized state

A

The pH of the LA solution and the pKa of the drug itself

59
Q

Areas with high pH will allow for faster/slower absorption

A

Faster (also greater amount)

60
Q

Why do LAs rarely work in infected tissues?

A

Infection tends to drive down the local pH and shifting much more drug into the ionized state

61
Q

Adding bicarb to a LA injection will do what

A

Increase speed of onset, enhances block depth, and increases the spread of the block

62
Q

Explain ion trapping in pregnancy

A

Fetal pH is lower than maternal pH and results in basic drugs (such as LA) becoming more ionized when they reach fetal circulation. This effectively traps them on the fetal side of the circulation since ionized molecules cannot easily cross the placenta. This also maintains a gradient for further diffusion.

63
Q

Potency main determinant

A

Lipid solubility

64
Q

Highly potent LAs

A

Etidocaine, bupivacaine, tetracaine

65
Q

What affects LA duration of action

A

Amount of time the LA is in contact with the nerve fiber
TIssue blood flow
Addition of vasoconstrictors
Lipid solubility
Protein binding (most important, increased PB–> increased DOA)
Intrinsic vasoconstrictor activity (Lido dilates, mepivacaine constricts)
Lung uptake (bupi, lido, prilo)
Metabolism

66
Q

LA and vasoconstrictors- three purposes

A

Inhibit system absorption
Prolong LA effect
Detection of intravascular injection

67
Q

Procaine Lipid sol, PB, DOA

A

1

5%

Short

68
Q

Chloroprocaine Lipid sol, PB, DOA

A

1

7%

Short

69
Q

Lidocaine Lipid sol, PB, DOA

A

4

65%

Moderate

70
Q

Mepivacaine Lipid sol, PB, DOA

A

1

75%

Moderate

71
Q

Tetracaine Lipid sol, PB, DOA

A

80

85%

Long

72
Q

Etidocaine Lipid sol, PB, DOA

A

140

95%

Long

73
Q

Bupivacaine Lipid sol, PB, DOA

A

30

95%

Long

74
Q

What determines LA con. in the blood

A

Concentration of LA administered

Tissue blood flow

75
Q

Ester metabolism

A

Primarily by pseudocholinesterases in the plasma (some in the liver)

Metabolite is PABA

Cocaine is the exception, primarily hepatic metabolism

76
Q

Amide metabolism

A

Liver microsomal enzymes

Slower, more complex than esters

hydroxylation, dealkylation, hydrolysis

More likely to create toxicity/accumulation effects

77
Q

Big summary for kinetics. Primary factor for-

Potency

DOA

Onset

A

Lipid solubility

Protein binding

pKa

78
Q

Bupi max dose

A

2.5mg/kg

79
Q

Ropi max dose

A

3mg/kg

3.5mg/kg with epi

80
Q

Etido max dose

A

4mg/kg

81
Q

Lido max dose

A

4mg/kg

7mg/kg with epi

82
Q

Mepi max dose

A

4mg/kg

7mg/kg with epi

83
Q

Chloro max dose

A

12mg/kg

84
Q

Cocaine max dose

A

3mg/kg

85
Q

Tetra max dose

A

3mg/kg

86
Q

LA toxicity

A

Mouth/tongue numbness, tinnitus, vision changes, dizziness, slurred speech, restlessness

Muscle twitching of face/extremities indicates imminent sz

Sz followed by CNS depression, apnea, hypotension

Treat with benzos

Cocaine will display restlessness, tremors, sz, euphoria (NE reuptake inhibited)

87
Q

What is transient neurologic symptoms (TNS)

A

Neuro-inflammatory process causing pain in lower back, butt, post. thighs, 24 hours after full SAB recovery. Lasts about a week.

88
Q

What is cauda equina syndrome

A

Diffuse lumbosacral injury, numbness in LE, loss of bladder/bowel control, paraplegia

89
Q

Which agents have been implicated in TNS and cauda equina syndrome

A

Lidocaine 5%, tetracaine, chloroprocaine

90
Q

LA CV toxicity

A

CV more resistant to LA toxicity than CNS

Hypotension (SNS depression), myocardial depression, AV block (SVR, CO decreased, wide PR/QRS, arrhythmias, CV collapse)

91
Q

Which agent is most CV toxic

A

Bupivacaine- at lower toxic doses, IV injection may cause cardiac arrest

92
Q

How does cocaine overdose affect the CV system

A

Massive INCREASE in SNS outflow. Coronary vasospasm, MI, dysrhythmias may result.

93
Q

Treatment of CV collapse in LA toxicity

A

Resuscitation often fails, prevention is the best medicine:
Small, incremental dosing
ASPIRATE
Watch for early EKG changes and STOP

Basic CPR immediately 
Modified ACLS (Epi, atropine, vaso only)

Intralipid 20% 1.5ml/kg rapid bolus immediately followed by 0.25mgml/kg/min for 10 minutes

94
Q

Allergic reactions to LAs

A

less than 1% incidence

High concentration vs true allergy

Esters more likely to cause (possible PABA link)

Preservatives also implicated (Methylparaben)

Epi?

Are not MH triggers

95
Q

LA interactions

A

Pseudocholinesterase inhibitors may prolong the duration of ester LAs

Cimetidine and propranolol decrease hepatic BF–> decreased clearance of amide LAs and cocaine

Clonidine, opioids, epi added to LA increase analgesic effect

96
Q

DOA from shortest to longest

A 
Chloro 30-60
Pro      45-60
Lido     60-120
Prilo     60-120
Mepi    90-180
Bupi     240-480
Ropi     240-480
97
Q

What other uses does lidocaine have?

A

Cough suppression
Attenuate ICP rise, BP rise with DVL
Attenuate bronchospasm that may occur with airway instrumentation
Suppression of ventricular dysrhythmias

98
Q

Cocaine

A 
Unique ester
Blocks NE and dopamine reuptake
CNS- euphoria
CV- stimulation
Hepatic metabolism

Still used in ENT surgery

99
Q

Procaine

A

Ester prototype
Used in spinals prior to development of lidocaine
NOT used much

pKa 8.9= 97% ionized, very slow onset
Short DOA
Hypersensitivity
Higher nausea risk
Higher incidence of CNS effects

Metabolite interferes with sulfonamide Abx

100
Q

Tetracaine

A

Spinal, corneal anesthesia
Long DOA, up to 6 hours with epi

Not popular in epidurals
Slow onset, profound motor block, toxicity risk with large doses

High incidence of TNS

101
Q

Chloroprocaine

A

Popular in OB epidurals- ultra rapid serum hydrolysis reduces tox. risk

Epidural, PNB where short duration is desired

Spinal being reinvestigated, but still considered off-label

Neurotoxicity is possibly related to preservative

102
Q

Lidocaine

A

Very popular- topical (4%), regional (0.25-0.5%), PNB (1-2%), spinal (1.5-5%), and epidural (1.5-2%)

Rapid onset, intermediate DOA

2 active metabolites- monoethylglycinexylidide (80% activity) and xylidide (10% activity)

Spinal use is still controversial, especially continuous spinal

103
Q

Mepivacaine

A

Similar to bupivacaine structurally
Similar to lidocaine clinically

Rapid onset
Less vasodilation= longer DOA (good when unable to use epi)
E 1/2 t about 2 hrs
Slightly more CNS toxicity compared to lidocaine
Not effective as a topical

104
Q

Prilocaine

A

Rapid metabolism leads to less CNS toxicity than lidocaine

Toxic metabolite ortho-toluidine
Avoid in OB

Doses over 600mg converts Hgh to methemoglobin
Give methylene blue 1-2mg/kg IV over 5 minutes

105
Q

Etidocaine

A

Used for PNB (0.5-1%) and epidurals (1-1.5%)

Highly lipid soluble, long acting with rapid onset (pKa=7.7)

106
Q

Bupivacaine

A

Longer DOA and longer onset compared to lido
Popular for differential blocks (sensory>motor)

Good choice for post-op pain, labor epidural

Used for spinal (0.5-0.75%), epidural (0.0625% pain to 0.5% for surgical block), PNB (0.25-0.5%)

Highly bound to alpha-1 glycoprotein

Very low incidence of CNS effects with spinal

Very cardiotoxic, use 0.5% of lower for PBN or epidural. Serum 1/2t is 3.5hrs, so be careful.

107
Q

Ropivacaine

A

S or levo enantiomer of bupivacaine with a propyl tail on the piperidine ring
Also good for differential block
Less cardiotoxic
More vasoconstriction

2 active metabolites, shorter e1/2t (2 hrs) compared to bupivacaine

Expensive

108
Q

Levobupivacaine

A

Just the S enantiomer of bupivacaine
Less cardiotoxic
E1/2t 2.6hrs
Even more expensive, save for when large doses are required

109
Q

Main considerations for dosing

A

Concentration, volume, and total dose given

110
Q

PNB dosing

A

Volume dictated by the type of block

Choose concentration based on the limitations of max dose balanced with the density of the block required

111
Q

Epidural dosing

A

Volume dictated to what level of block is desired

1.25-1.6ml per segment desired (count 1 direction)

Choose concentration based on density of block desired

112
Q

Spinal

A

Just have to know these doses

Summer '14 Pharm III (7 decks)

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