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KM (Spring 2024) Anesthesia Pharm ** > Local Anesthetics I (Exam IV) > Flashcards

Local Anesthetics I (Exam IV) Flashcards

1
Q

What was the first local anesthetic?

A

Cocaine

S3

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2
Q

Is cocaine an ester or amide?

A

Cocaine is an ester.

S3

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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.

S3

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4
Q

What was the first synthetic ester developed in 1905?

A

Procaine

S3

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5
Q

What was the first synthetic amide developed in 1943?

A

Lidocaine

Gold Standard

S3

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6
Q

What are the uses for Local Anesthetics (LAs)?

A
  • Treat dysrhythmias
  • Analgesia: Acute and chronic pain
  • Anesthesia- ANS Blockade, Sensory Anesthesia, Skeletal Muscle Paralysis

S4

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7
Q

What antiarrhythmic Drug Class is lidocaine in?

A

Class I: Sodium Channel Blockers

S4

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8
Q

MAGA: What is the intra-op infusion dose of lidocaine?

A

1 mg/kg over an hour

S5

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9
Q

What is the IV dose of Lidocaine?

A
  • 1 to 2 mg/kg IV (initial bolus) over 2 - 4 min.
  • 1 to 2 mg/kg/hour (drip)

S7

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10
Q

When should lidocaine be terminated?

A

Terminate within 12 - 72 hours

S7

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11
Q

Dose Dependent Effects of Lidocaine if plasma lidocaine concentration is 1-5 mcg/ml.

A

Analgesia

S8

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12
Q

Dose Dependent Effects of Lidocaine if plasma lidocaine concentration is 5-10 mcg/ml.

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

S8

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13
Q

Dose Dependent Effects of Lidocaine if plasma lidocaine concentration is 10-15 mcg/ml.

A
  • Seizures
  • Unconsciousness

S8

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14
Q

Dose Dependent Effects of Lidocaine if plasma lidocaine concentration is 15-25 mcg/ml.

A
  • Apnea
  • Coma

S8

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15
Q

Dose Dependent Effects of Lidocaine if plasma lidocaine concentration is >25 mcg/ml.

A
  • Cardiovascular Depression

S8

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16
Q

Describe the components that make up the molecular structure of lidocaine.

A

Lipophilic Portion (Aromatic Section)
Hydrocarbon Chain
Hydrophilic (Amino Group)

Bond between the lipophilic portion and the hydrocarbon chain will determine if LA is an ester or an amide.

S9 VERIFY!!!!

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17
Q

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

A

Bond between the lipophilic portion and the hydrocarbon chain will determine if LA is an ester or an amide.

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18
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

S10

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19
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

S10

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20
Q

Local anesthetics will typically have a pH of _____ and are weak _______. ?

A

pH of 6; weak bases

A majority of LA are weak bases

S11

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21
Q

Increased potency generally correlates to increased __________.

A

duration

S12

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22
Q

What is the potency, onset, DOA, Max single dose of each LA?

A
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23
Q

Which ester is the most potent?

A

Tetracaine

S12

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24
Q

Which local anesthetics will exhibit the highest degree of protein binding?

A
  • Bupivacaine
  • Levobupivacaine
  • Ropivacaine

S12

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25
Q

Which two local anesthetics will have the most rapid onset?

A

Chloroprocaine
Lidocaine

S12

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26
Q

Which 3 LA will have the highest protein binding?

A

Levobupivacaine (>97%)
Bupivacaine (95%)
Ropivacaine (94%)

S12

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27
Q

Lipid solubility correlates to _______ of the drug.

Which LA has the highest lipid solubility?

A
  • potency
  • Tetracaine

S12

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28
Q

Lipid solubility

A
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29
Q

pK values closer to a pH of ___________ will have the fastest onset of action.

A

7.35 - 7.45

S13

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30
Q

Which three local anesthetics have pK values closest to 7.35-7.45 ?

A
  • Lidocaine (pK = 7.9)
  • Prilocaine (pK = 7.9)
  • Mepivacaine (pK = 7.6)

S13

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31
Q

Which ester has the greatest degree of lipid solubility?

A

Tetracaine

S12/13

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32
Q

Which amide has the greatest degree of lipid solubility?

A

Bupivacaine

S12/13

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33
Q

How do liposomes and local anesthetics interact?
What is the result?

A
  • Liposomes unload LA’s into tissue at a controlled rate.
  • Prolonged duration of action & decreased toxicity

S15

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34
Q

The FDA released this local anesthetic that contains liposomes and can last up to 96 hours.

A

Exparel ER (Bupivacaine)

S15

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35
Q

What is the mechanism of action of Local Anesthetics?

A
  • Binds to inactivated, closed voltage-gated Na+ channels@ inner gate
  • Block/inhibit Na+ passage in nerve membranes

LA must be non-ionized and lipid-soluble to go through the cell membrane and block the Na+ gated channel from within the cell.

S16

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36
Q

What two things will cause a local anesthetic to not work anymore?

A

Becoming water-soluble and ionized.

??

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37
Q

What factors affect the degree of blockade seen from local anesthetics?

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

S18

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38
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.

??

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39
Q

What other receptors can be targeted by local anesthetics besides sodium channels?

A
  • Potassium channels
  • Calcium Ion Channels
  • G protein-coupled receptors

S18 - don’t need to truly memorize

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40
Q

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

A

MAC

S20

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41
Q

What component of the local anesthetic is required for the conduction block?

A

Non-ionized form (equates with lipid solubility)

??

42
Q

Larger fibers need _____ concentrations of LAs.

A

higher

S20

43
Q

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

A

2x

S20

44
Q

How many nodes of Ranvier need to be blocked to equate to 1 cm of local anesthesia?

A

At least 2, preferably 3 Nodes of Ranvier to prevent the conduction (Minimum Effect Concentration)

S20

45
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 tachycardia

S21

46
Q

What fibers are blocked if the patient can’t tell if they are being poked by a sharp needle?

A
  • Myelinated A and B fibers

S21

47
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

S21

48
Q

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

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

S21

49
Q

Which patient population will have increased sensitivity and be harder to block?

A

Pregnancy

Harder or easier?

S21

50
Q

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

A

more

S22

51
Q

Because the pKA of LA’s are 8, less than ______% of the drug is in lipid-soluble nonionized form.

A

50%

S22

52
Q

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

What happens to the duration of action?

A

LA is less potent

↓ Duration of action

S22

53
Q

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

A

greater

S22

54
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

S22

55
Q

Factors that influence the absorption of LA.

A
  • Site of injection
  • Dosage
  • Epinephrine use
  • Pharmacologic characteristics of the drug

S23

56
Q

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

A

S23

57
Q

________is the primary determinant of potency

A

Lipid solubility

S24

58
Q

The rate of clearance is dependent on what two factors?

A
  • Cardiac output
  • Protein binding:

Note: % bound is inversely related to % plasma.

(40% albumin-bound means 60% will float freely in plasma.)

S25

59
Q

Which ester LA will metabolize the fastest?

A

Chloroprocaine > Procaine d/t the smallest % of protein binding.

S26

60
Q

Which amides will metabolize the slowest?

A
  • Bupivacaine
  • Levobupivacaine
  • Ropivacaine

S26

61
Q

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

A

Re-dosing of LA

S27??

62
Q

Where are Amide local anesthetics metabolized?

A

Liver via CYP 450’s

S27

63
Q

Which Amide is most rapidly metabolized?

A

Prilocaine (lowest protein binding)

64
Q

Which Amides exhibit intermediate metabolism?

A
  • Lidocaine
  • Mepivacaine

S27

65
Q

Which Amides exhibit the slowest metabolism?

A
  • Bupivacaine
  • Ropivacaine

S27

66
Q

How are esters metabolized?

A

Hydrolyzed by cholinesterases in plasma

S28

67
Q

Cocaine, being an ester, is primarily metabolized via plasma cholinesterases. T/F?

A

False. Primarily hydrolyzed by liver cholinesterases > plasma cholinesterases. All other esters hydrolyzed by plasma > liver

S28

68
Q

What is the metabolite of esters?

What is the significance of this metabolite?

A
  • ParaAminoBenzoic acid (PABA)
  • Common cause of Allergies

S28

69
Q

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

A

No

S28

70
Q

Are amides or esters, generally slower at metabolizing?

A

Amides are slower at metabolism.

(CYP450s instead of plasma cholinesterases)

S28

71
Q

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

A
  • Lidocaine
  • Bupivacaine (dose dependent)
  • Prilocaine

S29

72
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 urine.

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.

S29

73
Q

In general, the more lipid soluble the local anesthetic is, the greater the potency. T/F

A

True

Question slide

74
Q

Which local anesthetic property is most important regarding the duration of action?

A

Lipid Solubility (most important)

protein binding is more cellular

Question slide

75
Q

Place the three factors below in order of importance for affecting duration of action?

  • Protein Binding
  • Clearance
  • Lipophilicity
A
  1. Lipid Solubility (most important)
  2. Clearance
  3. Protein binding

???

76
Q

How will pregnancy affect
plasma cholinesterase levels?

A

Lower levels of plasma cholinesterases

Caution with LA that are esters, bigger impact with normal doses

Ester LAs are still given to pregnant women because the effects of the amide LAs are detrimental to the fetus.

S30

77
Q

What classification of LAs is more likely to cause ion trapping thus affecting fetal health?

A

Amides

Ion trapping will lead to LA toxicity in the placenta.

S30

78
Q

What is ion trapping?

A

The pH in the fetal environment is more acidic than in maternal circulation.

S30

79
Q

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

A

Sodium Bicarb

S30

80
Q

Bupivacaine
Protein Bound:
Arterial Concentration:

A

Bupivacaine
Protein Bound: 95%
Arterial Concentration: 0.32

S31

81
Q

Lidocaine
Protein Bound :
Arterial Concentration:

A

Lidocaine
Protein Bound: 70%
Arterial Concentration: 0.73

S31

82
Q

Prilocaine
Protein Bound:
Arterial Concentration:

A

Prilocaine
Protein Bound: 55%
Arterial Concentration: 0.85

S31

83
Q

What is the major metabolite of lidocaine?

A

Xylidide

S32

84
Q

What is Lidocaine’s max infiltration dose?

A
  • 300 mg solo
  • 500 mg with epi

S32

85
Q

Lidocaine will have prolonged clearance with ______

A

Pregnancy Induced Hypertension

S32

86
Q

What is prilocaine’s primary metabolite?

What is the issue with this metabolite?

A

Metabolite: Orthotoluidine

The metabolite converts Hemoglobin to Methemoglobin, resulting in Methemoglobinemia.

S33

87
Q

What is the result of Methemoglobinemia?

A

Fe3+ (ferric iron) is not capable of carrying O2

Cyanosis

S33

88
Q

What is the max dose of prilocaine to cause Methemoglobinemia?

A

600 mgs

S33

89
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 8 mg/kg (over 24 hours)

S33

90
Q

Mepivacaine is similar to Lidocaine except:

A
  • Longer duration of action
  • Lacks vasodilator activity

S34

91
Q

Can Mepivacaine be given in pregnant patients?

A

No. Prolonged elimination in fetus

S34

92
Q

What plasma protein does Bupivacaine bind to?

A

95% bound to α1-Acid glycoprotein

S34

93
Q

Ropivacaine
Metabolism:

Metabolite:

Protein Binding

A

Ropivacaine
Metabolism: Hepatic cytochrome P450 enzymes

Metabolites: Can accumulate with uremic patients
Lesser system toxicity than Bupivacaine

Protein Binding: α1-acid glycoprotein

S35

94
Q

Dibucaine
Metabolism:
MOA:

A

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

S35

95
Q

What is procaine’s primary metabolite?

A

PABA

S36

96
Q

Tetracaine metabolism is slower than ______

A

Procaine

S36

97
Q

Which of the following local anesthetics will have the highest rate of metabolism through hydrolysis?

Procaine
Chloroprocaine
Tetracaine

A

Chloroprocaine (fastest level of metabolism) > procaine > tetracaine (slowest)

S36

98
Q

What is Benzocaine used for?

A

Topical anesthesia of mucous membranes

Tracheal intubation
Endoscopy,
Transesophageal echocardiography (TEE)
Bronchoscopy

S37

99
Q

Overdose of Benzocaine can lead to ________.

A

OD of Benzocaine can lead to Methemoglobinemia

S37

100
Q

What makes Benzocaine unique?

A

Weak acid instead of a weak base, like most LA.
pKa = 3.5

S37

101
Q

How is cocaine metabolized?

Who should receive decreased amounts of cocaine?

A

Metabolized by liver cholinesterase > plasma cholinesterase

Decrease cocaine use in parturients, neonates, the elderly, and severe hepatic disease

S38

102
Q

When should one be cautious when administering cocaine?

A

Cocaine can cause coronary vasospasm, ventricular dysrhythmias, HTN, tachycardia, and CAD.

S38

KM (Spring 2024) Anesthesia Pharm ** (101 decks)

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