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SPR25: Anesthetic Pharm > SS25 Local Anesthetics I (Exam 4) > Flashcards

SS25 Local Anesthetics I (Exam 4) Flashcards

1
Q

First local anesthetic (LA)

A
  • Cocaine
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2
Q

Is Cocaine an Ester or Amide?

A

ESTER

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3
Q

What was cocaine first used for and what was the effect?

A
  • Ophthalmology (1884)
  • Local vasoconstriction: shrink nasal mucosa
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4
Q

First synthetic ESTER developed in 1905

A

PROCAINE

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5
Q

First synthetic AMIDE developed in 1943

A

LIDOCAINE

  • Became gold standard for all other LAs
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6
Q

What drug class is associated with each Antiarryhthmic class:
- Class I
- Class II
- Class III
- Class IV
- Miscellaneous

Hint: 1 class per group

A
  • Class I: Na-channel blockers
  • Class II: βeta blockers
  • Class III: K-channel blockers
  • Class IV: Calcium-channel (CaC) blockers
  • Miscellaneous: Adenosine, Electrolyte supplements, digitalis compunds (Cardiac glycosides)
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7
Q

What are the uses for LAs?

A
  • Treat dysrhythmias
  • Analgesia: Acute and Chronic pain
  • Anesthesia: ANS Blockade, Sensory Anesthesia, Skeletal Muscle Paralysis
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8
Q

LIDOCAINE: Antiarrhythmic Drug Class

A

Class I: Sodium-channel Blockers

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9
Q

What is the intra-op infusion dose of lidocaine (multi-modal)?

A

1 mg/kg over an hour

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10
Q

Lidocaine: Bolus dose and infusion dose

A
  • Bolus: 1 to 2 mg/kg IV over 2 - 4 min
  • Infusion: 1 to 2 mg/kg/hr over 12 to 72 hrs
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11
Q

When should the Lidocaine infusion be terminated?
- Which organ systems need to be monitored closely?

A
  • Terminate within 12 - 72 hours
  • Cardiac, Hepatic, Renal dysfunction
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12
Q

Dose-dependent effects of plasma Lidocaine concentration @ 1 - 5 mcg/ml:

A

Analgesia

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13
Q

Dose-dependent effects of plasma Lidocaine concentration @ 5 - 10 mcg/ml:

A
  • Circum-oral numbness
  • Tinnitus
  • Skeletal muscle twitching
  • Systemic hypotension
  • Myocardial depression
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14
Q

Dose-dependent effects of plasma Lidocaine concentration @ 10 - 15 mcg/ml:

A
  • Seizures
  • Unconsciousness
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15
Q

Dose-dependent effects of plasma Lidocaine concentration @ 15 - 25 mcg/ml :

A
  • Apnea
  • Coma
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16
Q

Dose-dependent effects of plasma Lidocaine concentration @ >25 mcg/ml :

A
  • Cardiovascular Depression
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17
Q

What is the molecular structure of LAs?

A
  • Lipophilic Portion (Aromatic ring)
  • Hydrocarbon Chain (intermediate chain bridging the lipophillic &. hydrophillic portions)
  • Hydrophilic (Tertiary Amino Group)
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18
Q

What structural component of a LA determines if it is an ester or an amide?
- Significance?

A
  • Bond between the lipophilic (aromatic) portion and the hydrocarbon chain will determine if LA is an ester or an amide
  • The classification effects clearance and metabolism

Side note: All esters have (1) i & all amides have (2) i’s

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19
Q

What type of local anesthetic would you anticipate from the figure below?

A

Ester due to the ester bond between the aromatic and the intermediate chain

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20
Q

What type of local anesthetic would you anticipate from the figure below?

A

Amide due to the amide bond between the aromatic and the intermediate chain

Side note: All esters have (1) i & all amides have (2) i’s

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21
Q

Bonus: Name these LA drugs based on molecular structure.

A
  • Top: Procaine
  • Bottom: Lidocaine
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22
Q

Majority of LA have a pH of ______ and are Weak ________.

A
  • pH of 6 (HCl salts)
  • Weak BASES

Side note: drug name + suffix chemical name = base;
prefix chemical name + drug name = acid

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23
Q

LA composition:

A
  • pH of 6
  • Epinephrine (local level)
  • Sodium Bisulfite - Increases Epinephrine solubilty and prevents precipitate formation from Epinephrine
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24
Q

Bonus: Which amide LA are chiral drugs?

A
  • Mepivacaine, Bupivacaine, Ropivacaine
  • All 3 contain assymetrical carbon atom
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25
Q

Increased potency generally correlates to increased __________.

A

Lipid solubility

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26
Q

Per lecture, at a pH of ________: (table trend)
-If ESTER, ↑ non-ionization % = ↑ potency
-If AMIDE, ↓ non-ionization % = ↑ potency

A
  • pH of 7.4
  • Amides with higher potency have higher lipid solubility & lower non-ionization fraction
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27
Q

Most potent LA?
- Class?
- Potency value?
- Lipid solubility?
- Protein binding?

A
  • Tetracaine = Ester
  • Potency = 16 b/c has highest lipid solubility (80)
  • PB: 76 %
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28
Q

Order esters from least to most potent. Include values.

A
  1. Procaine -1
  2. Chloroprocaine - 4
  3. Tetracaine - 16

**Hint: Factor of 4*

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29
Q

Order amides from least to most potent. Include values.

A
  • Least:
    -Lidocaine = Prilocaine = Mepivacaine - 1
  • Most:
    -Bupivacaine = Levobupivacaine =Ropivacaine - 4

Hint: Factor of 4

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30
Q

Which 3 Amides LA will exhibit the highest degree of protein binding? Place in order from least to most.
- What trends are associated with these 3 amides ?

A
  1. Ropivacaine - 94 %
  2. Bupivacaine - 95 %
  3. Levobupivacaine - ( > 97 %)

↑protein binding = ↑ potency, ↓ single dose, ↓onset, ↑ duration, ↑ pk

Most potent Amides have highest protein bindings

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31
Q

Which Amide LA has lowest degree of protein binding?
- Lipid solubility?
- What effect does it have on Vd?

A
  • Prilocaine - 55 %
  • Vd = 191 L (highest Vd among all other LA) d/t very low lipid solubility (0.9) and protein binding
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32
Q
  • Only ester LA with rapid onset?
  • Only amide LA with rapid onset?
A
  • Ester: Chloroprocaine
  • Amide: Lidocaine
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33
Q

What are the pk values for the following Ester LA?
- Procaine
- Chloroprocaine
- Tetracaine

A
  • Procaine 8.9
  • Chloroprocaine 8.7
  • Tetracaine 8.5
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34
Q

What are the pk values for the following Amides LA?
- Lidocaine
- Prilocaine
- Mepivacaine
- Bupivacaine
- Levobupivacaine
- Ropivacaine

A
  • Lidocaine 7.9
  • Prilocaine 7.9
  • Mepivacaine 7.6
  • Bupivacaine 8.1
  • Levobupivacaine 8.1
  • Ropivacaine 8.1
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35
Q

Which Amide has the greatest degree of lipid solubility?
- Compare potency and duration of action to Lidocaine? (Greater or less)

A
  • Bupivacaine (28)
  • Greater potency & longer duration of action > Lidocaine
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36
Q

Nonionized % @ pH of 7.4:
- Procaine
- Chloroprocaine
- Tetracaine

A
  • Procaine = 3 %
  • Chloroprocaine = 5 %
  • Tetracaine = 7 %
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37
Q

Nonionized % @ pH of 7.4:
- Lidocaine
- Prilocaine
- Mepivacaine
- Bupivacaine
- Levobupivacaine
- Ropivacaine

A
  • Lidocaine 25 %
  • Prilocaine 24 %
  • Mepivacaine 39 %
  • Bupivacaine 17 %
  • Levobupivacaine 17 %
  • Ropivacaine - 17 %
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38
Q

Procaine:
- duration of action:
- max single dose for infiltration:
- Elimination half-time:
- protein binding %
- Vd
- Lipid solubility

A
  • 45 - 60 min
  • 500 mg
  • 9 min
  • PB: 6 %
  • Vd 65 L
  • Lipid solubility 0.9

Highest Vd & Lowest lipid solubility among Esters

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39
Q

Chloroprocaine
- duration of action:
- max single dose for infiltration:
- Elimination half-time:
- protein binding %
- Vd
- Lipid solubility

A
  • 30 - 45 mins (most rapid overall)
  • max dose: 600 mg
  • 7 min (Fastest)
  • n/a
  • 35 L (lowest ester Vd)
  • n/a
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40
Q

Tetracaine:
- duration of action
- max single dose for infiltration
- Elimination half-time
- protein binding %
- Vd
- Lipid solubility

A
  • 60 - 80 min (longest ester)
  • 100 mg Topical
  • n/a
  • 76%
  • n/a
  • 80
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41
Q

duration of action of Amide LA:
- Lidocaine
- Prilocaine
- Mepivacaine
- Bupivacaine
- Levobupivacaine
- Ropivacaine

A
  • Lidocaine: 60 - 120 mins
  • Prilocaine: 60 - 120 mins
  • Mepivacaine: 90 -180 mins
  • Bupivacaine: 240 - 480 mins
  • Levobupivacaine: 240 - 480 mins
  • Ropivacaine: 240 - 480 mins
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42
Q

Lidocaine
- max single dose for infiltration:
- Elimination half-time:
- protein binding %
- Vd
- Lipid solubility
- Clearance

A
  • 300 mg (500 mg w/ Epi)
  • 96 min
  • 70 %
  • 91 L
  • 2.9
  • 0.95 L/min

Lidocaine & Prilocaine: SAME potency, duration, pK, & elimination half time

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43
Q

Prilocaine
- max single dose for infiltration:
- Elimination half-time:
- protein binding %
- Vd
- Lipid solubility

A
  • 600 mg (highest max)
  • 96 min
  • 55 %
  • 191 L (highest Vd)
  • 0.9
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44
Q

Mepivacaine
- max single dose for infiltration:
- Elimination half-time:
- protein binding %
- Vd
- Lipid solubility
- Clearance

A
  • 400 mg (500 mg w/ Epi)
  • 114 min
  • 77 %
  • 84 L
  • 1
  • 9.78 L/min (highest)
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45
Q

Bupivacaine
- max single dose for infiltration:
- Elimination half-time:
- protein binding %
- Vd
- Lipid solubility
- Clearance

A
  • 175 mg (225 mg w/ Epi)
  • 210 min (longest)
  • 95 %
  • 73 L
  • 28
  • 0.47 L/min
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46
Q

Levobupovacaine
- max single dose for infiltration:
- Elimination half-time:
- protein binding %
- Vd

A
  • 175 mg (225 mg w/ Epi)
  • 156 min
  • > 97%
  • 55 L (lowest amide Vd)
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47
Q

Ropivacaine
- max single dose for infiltration:
- Elimination half-time:
- protein binding %
- Vd

A
  • 200 mg
  • 108 mins
  • 94 %
  • 59 L
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48
Q

Table to Review

A
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49
Q

Table to review

A
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50
Q

How do liposomes & LA interact?
- What is the result?

A
  • Liposomes unload a higher amount of LA into molecule & have consistent, controlled release of LA into tissues
  • Prolonged duration (extended release: ER) & decreased toxicity
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51
Q

Which LAs are being linked to Liposomes? (3)

A
  • Lidocaine: gold standard
  • Tetracaine: Most potent LA
  • Bupivacaine: > potentcy Lidocaine
52
Q

The FDA released this LA that contains liposomes.
- What is the duration of action?

A
  • Exparel (Bupivacaine ER)
  • Duration up to 96hrs
53
Q

LA: MOA?

A
  • Binds to inner, inactivated closed gate of V-G Na+ channels
  • Block/inhibit Na+ passage in nerve membranes → slows rate of depolrization → unable to reach threshold → no action potential
54
Q

LA must be ___________ and ____________ to go through the cell membrane and block the Na+ gated channel from within the cell

A
  • non-ionized, lipid-soluble
55
Q

What two factors will cause a LA to not work anymore?

A
  • Becoming water-soluble and ionized.
56
Q

What (3) factors affect the degree of LA blockades?

A
  • Lipid solubility or non-ionized form
  • Repetitively stimulated nerve (↑ sensitivity)
  • Diameter of the nerve (↑ diameter = ↑ LA need)
57
Q

What happens when you expose LA (a weak base) to an acidic environment?

A
  • LA becomes ionized
  • When LA becomes ionized, it will not cross cell membrane to block Na+ gated channels
58
Q

What component of the LA is required for the conduction block?

A

Non-ionized form

59
Q

What other receptors can be targeted by LA besides V-G Sodium channels?

A
  • Potassium channels
  • Calcium Ion Channels
  • G protein-coupled receptors (GCPRs)
60
Q

Minimum Effective Concentration (MEC or Cm) (LAs) = _________ (Volatile Agents)

A

Minimum Alveolar Concentration (MAC)

61
Q

Larger fibers need _____ concentrations of LAs.

62
Q

The diameter of motor nerve is how many times larger than the diameter of the sensory nerve?

63
Q

How many nodes of Ranvier need to be blocked to equate to 1 cm?
- What type of LA administration might require more?

A
  • In terms of a general incision, 3 Nodes of Ranvier to prevent the conduction (at least 2)
  • Peripheral Nerve Block (PNB) requires introducing LA around entire nerve or set
64
Q

Which fibers do LAs block?

A
  • Preganglionic B fibers = fastest
  • Myelinated A = Medium
  • Myelinated B-fibers = faster
  • Myelinated A-δ & Unmyelinated C-fibers = small
  • Alters pain, temperature, touch/pressure, proprioception, & motor
65
Q

If a LA were given intravascularly, which fibers would be affected the fastest?

What signs and symptoms would you see?

A
  • Pre-ganglionic B fibers (SNS)
  • Hypotension and bradycardia
66
Q

T/F: Pregnancy increases sensitivity to LA making it hard to block.

67
Q

What nerve types are typically affected last when administering LA through the epidural/spinal?

What sensations are the last to be affected?

A
  • Myelinated A-δ and unmyelinated C-fibers
  • Proprioception and Motor
68
Q

Place in order the fibers that are affected first to last when administering a local anesthetic.

A
  1. Preganglionic B fibers
  2. A-myelinated fibers and B fibers
  3. Myelinated A-δ and unmyelinated C-fibers
69
Q

pKa values closer to physiologic pH result in a _____ rapid onset

70
Q

Because the pKA of LA’s are above physiologic pH, only about ______% of the drug is in lipid-soluble nonionized form.

71
Q

If a LA has vasodilator activity, what happens to its potency?

What happens to the duration of action?

A
  • Vasodilatory activity decreases potency of LA && prolongs duration
72
Q

Because Lidocaine is a vasodilator, it will have ________ systemic absorption.

A
  • greater so less potency that bupivancaine
73
Q

Because Lidocaine has vasodilator activity, there is (greater/less) _______ systemic absorption. Resulting in a (shorter/longer) ________ duration of action at the site of injection.

A
  • greater
  • shorter
74
Q

Factors that influence the absorption of LA.

A
  • Site of injection
  • Dosage
  • Use of Epinephrine: usually give 5 mcg/mL to counteract vasodilation of LA → prolongs/enhances the
  • Pharmacologic characteristics of the drug
75
Q

List the uptake of Local Anesthetics Based on Regional Anesthesia Technique from highest to lowest blood concentration.

A
  1. IV
  2. Trachea- highly vascularized
  3. Caudal
  4. Paracervical
  5. Epidural
  6. Brachial
  7. Sciatic
  8. Subcutaneous

MEMORIZE

76
Q

Which pharmalogic characteristic of LAs is the primary determinant of potency that directly affects tissue distrubution?

A
  • Lipid solubilty by rate of distribtution
77
Q

The rate of clearance is dependent on what two factors?

A
  • Cardiac output (HTN = lower CO b/c it’s pushing against a higher SVR = low CL)
  • Protein binding %
78
Q

What is the relationship b/w protein binding and clearance?

A
  • PB % is inversely related to % plasma concentration

**Per Dr. Castillo↑ Protein binding = ↓ clearance from primary site of action **

79
Q

Where are Amide local anesthetics metabolized?

A

Liver via microsomal enzymes (CYP 450)

80
Q

T/F: Amides and Esters metabolize at the same rate.

A
  • FALSE
  • Amides metabolize slower than Esters b/c their metabolism is through the liver
  • Esters metabolism is via hydrolysis by cholinesterase enzymes in plasma
81
Q

Why is it important to know the metabolizing rate of LA?

A
  • Re-dosing of LA
82
Q

Which amide LA will metabolize the fastest?

A

Prilocaine d/t ↓ PB (55%)

83
Q

Which Amides exhibit intermediate metabolism?

A
  • Lidocaine
  • Mepivacaine
84
Q

Which Amides exhibit the slowest metabolism?

A
  • Etidocaine
  • Bupivacaine
  • Ropivacaine
85
Q

Again, how are Esters metabolized?

A
  • Hydrolyzed by cholinesterases in plasma
86
Q

Which ester is the exception to plasmaesterase and is metabolized by the liver?

87
Q

What is the metabolite of Ester LAs?
- What is the significance of this metabolite?

A
  • Para-aminobenzoic acid (PABA)
  • Common cause of Allergic reaction
88
Q

Is there cross-sensitivity between an amide allergy to an ester allergy?

89
Q

What are the most common LAs that have first-pass pulmonary extraction?

A
  • Pulmonary extraction = LAs are in the lungs and inactive which includes:
  • Lidocaine
  • Bupivacaine (dose-dependent)
  • Prilocaine
90
Q

Recap: What’s First-Pass Pulmonary Extraction?

A
  • Lung acts as a reservoir for LA.
  • Disconjugates, hydrolyzes, and/or metabolizes into inactive form so when drug leaves lung it is not effective.
91
Q

The poor water solubility of local anesthetics usually limits renal excretion of unchanged drug to less than ______%

The exception is ______, of which 10% to 12% of unchanged drug can be recovered in urine.

Water-soluble metabolites of local anesthetics, such as _______ resulting from metabolism of ester local anesthetics, are readily excreted in _______.

A

The poor water solubility of local anesthetics usually limits renal excretion of unchanged drug to less than 5%

The exception is cocaine, of which 10% to 12% of unchanged drug can be recovered in urine.

Water-soluble metabolites of local anesthetics, such as PABA resulting from metabolism of ester local anesthetics, are readily excreted in urine.

Renal Elimination and Clearance from body concept

92
Q

T/F: The more lipid soluble the LA is, the greater the potency.

A

True

MUST UNDERSTAND THIS!

93
Q

Which local anesthetic property is most important regarding the POTENCY

A

Lipid Solubility (most important)

94
Q

Which factor is most important for affecting Duration of Action?

  • Protein Binding or Clearance
A
  1. Protein binding = MOST IMPORTANT
  2. Clearance from primary site of action (ie: tooth anesthetic)
95
Q

Lets make sure we understand:
- High lipid solubility = _______?

A
  • ↑lipid soubility = ↑potency
96
Q

T/F: ↑ Protein binding capacity % = ↓ duration of action.

A
  • FALSE
    -↑Protein binding % = ↑ duration of action
97
Q

What class of LA should be used on a expecting mother if necessary?

98
Q

How will pregnancy affect
plasma cholinesterase levels?

A
  • Lower levels of plasma cholinesterase are seen in pregnancy
  • Mainly Amides LA transfer over to acidic fetal enviro. via transplacental transfer → Acid causes LA to convert to ionized form → severe fetal acidosis and ion trapping
  • can lead to profound fetal bradycardia, coma/death
99
Q

If there is ion trapping in the placenta, what can be given to adjust the pH?

A

Sodium Bicarb

100
Q

The ↑ protein binding %, the _____ arterial concentration.

A
  • lower

The ↑ the protein binding capacity, the less the drug is available to be metabolized, hence the lower the arterial concentration, keeping it in the system longer

101
Q

Bupivacaine
Protein Bound:
Arterial Concentration:

A

Bupivacaine
Protein Bound: 95%
Arterial Concentration: 0.32

102
Q

Lidocaine
Protein Bound :
Arterial Concentration:

A

Lidocaine
Protein Bound: 70%
Arterial Concentration: 0.73

103
Q

Prilocaine
Protein Bound:
Arterial Concentration:

A

Prilocaine
Protein Bound: 55%
Arterial Concentration: 0.85

104
Q

How is Lidocaine metabolized?
- What is the major metabolite of lidocaine?

A
  • Oxidative Dealkylation in liver, then Hydrolysis
  • Metabolite: Xylidide

Liver dx will affect metabolism & elimination

105
Q

What is Lidocaine’s max infiltration dose?

A
  • 300 mg solo/plain
  • 500 mg with Epinephrine (prolongs duration of action)
106
Q

Lidocaine will have prolonged clearance with ______ (complication).

A

Pregnancy Induced Hypertension (decreased CO)

107
Q

What is prilocaine’s primary metabolite?

What is the issue with this metabolite?

A

Metabolite: Orthotoluidine

The metabolite converts Hemoglobin to Methemoglobin → Methemoglobinemia

108
Q

What is the result of Methemoglobinemia?

A
  • Fe3+ (Ferric iron) is not capable of carrying O2 → decreased O2-carying capacity = Cyanosis
109
Q

What is the max dose of prilocaine?

110
Q

What is the treatment for Methemoglobinemia secondary to Prilocaine overdose?

A
  • Methylene Blue
  • 1 to 2 mg/kg IV over 5 mins (initial dose)
  • Total dose not to exceed 7 - 8 mg/kg
111
Q

Mepivacaine is similar to Lidocaine except:

A
  • Longer duration of action
  • Lacks vasodilator activity
  • Longer elimination in fetus; contraindicated in OB
112
Q

What plasma protein does Bupivacaine bind to?

A
  • 95% bound to α1-Acid glycoprotein
113
Q

Bupivacaine: Metabolism

A
  • Aromatic hydroxylation
  • N-Dealkyklation
  • Amide Hydrolysis
  • Conjugation via liver

CAAN

114
Q

Ropivacaine:
- Metabolism:
- Metabolite:
- Protein Binding:

A
  • Metabolism: Hepatic CYP450
  • Metabolites: Can accumulate with uremic patients (lesser system toxicity than Bupivacaine)
  • Protein Binding: 94% bound to α1-Acid glycoprotein
115
Q

Dibucaine
Metabolism:
MOA:

A

Metabolism: Liver
MOA: Inhibits the activity of normal butyrylcholinesterase (plasma cholinesterase) by more than 70%

116
Q

Procaine: Metabolite
- clinical significance?

A
  • PABA
  • Excreted unchanged in urine
117
Q

Order following LA in order of metabilism rate (high to low).
- Procaine
- Chloroprocaine
- Tetracaine
- What process is used for metabolism?

A
  1. Chloroprocaine = 3.5x faster
  2. Procaine
  3. Tetracaine (slowest
  • These are all metabolized via Hydrolysis (Pregnancy decreases plasma cholinesterase by 40%)

CPT

118
Q

What is Benzocaine used for?

A

Topical anesthesia of mucous membranes:
- ETI
- Endoscopy
- TEE
- Bronch

119
Q

Benzocaine:
- dose
- onset
- duration

A
  • Brief 1 second spray (20%) = 200 to 300 mg
  • onset: rapid
  • duration: 30 - 60 mins
120
Q

Overdose of Benzocaine can lead to ________.

A

Methemoglobinemia

121
Q

What is the max dose of Methylene Blue on a 65 y/o, 120 lb, male patient? in mg.

A

~ 432 mg or 436.4 mg total

122
Q

What makes Benzocaine unique?

A
  • Weak acid instead of a weak base, like most LA.
    pKa = 3.5
123
Q

Cocaine:
- Peak:
- Duration:
- Elimination:

A
  • Peak: 30-45 mins
  • Duration: 60 mins
  • Elimination: Urine (24 - 36 hrs)
124
Q

Cocaine adverse effects:

A
  • CARDIAC
  • Causes Coronary vasospasm, ventricular dysrhythmias, HTN, tachycardia, and CAD
125
Q

Cocaine:
- Metabolism:
- Who should receive decreased amounts of cocaine?

A
  • Metabolized by liver cholinesterase > plasma cholinesterase
  • Decrease cocaine use in Parturients (women in labor), Neonates, Elderly, and Severe Hepatic disease

SPR25: Anesthetic Pharm (10 decks)

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