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Spr24 Pharm II > Local Anesthetics I (Exam IV) Andy's Cards > Flashcards

Local Anesthetics I (Exam IV) Andy's Cards Flashcards

1
Q

What was the first local anesthetic?

A

Cocaine

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2
Q

Is cocaine an ester or amide?

A

Cocaine is an 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

What was the first synthetic ester developed in 1905?

A

Procaine

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5
Q

What was the first synthetic amide developed in 1943?

A

Lidocaine

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6
Q

What are the uses for Local Anesthetics (LAs)?

A
  • Anti-dysrhythmia
  • Analgesia: Acute and chronic pain
  • Anesthesia- ANS Blockade, Sensory Anesthesia, Skeletal Muscle Paralysis
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7
Q

What antiarrhythmic Drug Class is lidocaine in?

A

Class I: Sodium Channel Blockers

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8
Q

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

A

1 mg/kg over an hour

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9
Q

What is the IV dose of Lidocaine? (bolus and drip)

A
  • 1 to 2 mg/kg IV (initial bolus) over 2 - 4 min.
  • 1 to 2 mg/kg/hour (drip)
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10
Q

When should a lidocaine drip be terminated?

A

Terminate within 12 - 72 hours

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11
Q

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

A

Analgesia

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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
  • Skeletal muscle twitching
  • Systemic hypotension
  • Myocardial depression
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13
Q

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

A
  • Seizures
  • Unconsciousness
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14
Q

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

A
  • Apnea
  • Coma
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15
Q

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

A
  • Cardiovascular Depression
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16
Q

Describe the components that make up the molecular structure of local anesthetics.

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.

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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 (-CO-) or an amide (-NHC-).

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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

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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

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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

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21
Q

Increased protein binding % generally correlates to increased __________.

A

duration

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22
Q

Which ester is the most potent?

A

Tetracaine

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23
Q

Which two local anesthetics will have the most rapid onset?

A

Chloroprocaine
Lidocaine

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24
Q

Which 3 LA will have the highest protein binding?

A

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

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25
Q

Lipid solubility correlates to _______ of the drug.

Which LA has the highest lipid solubility?

A
  • potency
  • Tetracaine
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26
Q

Which three local anesthetics have the lowest pK values of the LAs?

A
  • Lidocaine (pK = 7.9)
  • Prilocaine (pK = 7.9)
  • Mepivacaine (pK = 7.6)
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27
Q

What is the pk for bupivacaine, levobupivacaine, and ropivacaine?

A

pk = 8.1

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28
Q

Which amide has the highest lipid solubility? Which ester has the highest lipid solubility?

A

amide: Bupivacaine

ester: Tetracaine

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29
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
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30
Q

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

A

Exparel ER (Bupivacaine)

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31
Q

What is the mechanism of action of Local Anesthetics?

A
  • Binds to voltage-gated Na+ channels
  • 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.

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32
Q

What will cause a local anesthetic to not work anymore?

A

Becoming ionized and water-soluble.

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33
Q

What 3 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)
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34
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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35
Q

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

A
  • Potassium channels
  • Calcium Ion Channels
  • G protein-coupled receptors
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36
Q

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

A

Non-ionized form (equates with lipid solubility)

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37
Q

Larger fibers need _____ concentrations of LAs.

A

higher

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38
Q

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

A

2x

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39
Q

How many nodes of Ranvier need to be blocked for MEC of local anesthesia?

A

At least 2, preferably 3 Nodes of Ranvier (1cm) to prevent the conduction (Minimum Effect Concentration)

40
Q

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

What signs and symptoms would you see?

A

Pre-ganglionic B fibers (SNS)

Hypotension and bradycardia

41
Q

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

A
  • A-𝛿 and A-β fibers
42
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-⍺ and A-𝛾
  • Proprioception and Motor
43
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-δ and unmyelinated C-fibers
  3. Myelinated A-⍺
44
Q

Which patient population will have increased sensitivity to blocks?

A

Pregnancy

45
Q

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

A

more

46
Q

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

A

50%

47
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

48
Q

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

A

greater

49
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
50
Q

Factors that influence the absorption of LA. (4)

A
  • Site of injection
  • Dosage
  • Epinephrine use
  • Pharmacologic characteristics of the drug
51
Q

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

A
52
Q

________is the primary determinant of potency

A

Lipid solubility

53
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.)

54
Q

How are amide LA’s generally metabolized?

A

microsomal enzymes in the liver (CYP450)

55
Q

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

A

Re-dosing of LA

56
Q

Which Amide is most rapidly metabolized?

A

Prilocaine

57
Q

Which Amides exhibit intermediate metabolism?

A
  • Lidocaine
  • Mepivacaine
58
Q

Which Amides exhibit the slowest metabolism?

A
  • Bupivacaine
  • Ropivacaine
59
Q

How are esters metabolized?

A

Hydrolyzed by cholinesterases in plasma > liver
(Except cocaine: more metabolism by liver)

60
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

61
Q

What is the metabolite of esters?

What is the significance of this metabolite?

A
  • ParaAminoBenzoic Acid (PABA)
  • Common cause of Allergies
62
Q

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

A

No

63
Q

Are amides or esters, generally slower at metabolizing?

A

Amides are slower at metabolism.

(CYP450s instead of plasma cholinesterases)

64
Q

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

A
  • Lidocaine
  • Bupivacaine (dose dependent)
  • Prilocaine
65
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% is unchanged drug 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% is unchanged drug in urine.

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

66
Q

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

A

True

67
Q

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

A

Protein Binding

68
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.

69
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.

70
Q

What is ion trapping?

A

The pH in the fetal environment is more acidic than in maternal circulation ⇒ LA crosses placenta and becomes ionized in acidic environment, unable to cross back

71
Q

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

A

Sodium Bicarb (alkalinize)

72
Q

Bupivacaine
Protein Bound:
Arterial Concentration:

A

Bupivacaine
Protein Bound: 95%
Arterial Concentration: 0.32

73
Q

Lidocaine
Protein Bound :
Arterial Concentration:

A

Lidocaine
Protein Bound: 70%
Arterial Concentration: 0.73

74
Q

Prilocaine
Protein Bound:
Arterial Concentration:

A

Prilocaine
Protein Bound: 55%
Arterial Concentration: 0.85

75
Q

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

A

Oxidative dealkylation in liver, then hydrolysis.

Metabolite: Xylidide

76
Q

What is Lidocaine’s max infiltration dose? (with and without Epi)

A
  • 300 mg plain
  • 500 mg with Epi
77
Q

Lidocaine will have prolonged clearance with ______

A

Pregnancy Induced Hypertension

78
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.

79
Q

What is the result of Methemoglobinemia?

A

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

Cyanosis, ↓O₂ carrying capacity

80
Q

What is the max dose of prilocaine?

A

600 mgs

81
Q

What is the treatment and dose 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
82
Q

Mepivacaine is similar to Lidocaine except:

A
  • Longer duration of action
  • Lacks vasodilator activity
83
Q

Can Mepivacaine be given in pregnant patients?

A

No. Prolonged elimination in fetus

84
Q

Bupivacaine
metabolism:
Protein Binding:

A

Bupivacaine
Metabolism: aromatic hydroxylation, N-dealkylation, amide hydrolysis, and conjugation

Protein binding: 95% bound to α1-Acid glycoprotein

85
Q

Ropivacaine
Metabolism:

Metabolite issue:

Protein Binding:

A

Ropivacaine
Metabolism: Hepatic cytochrome P450 enzymes

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

Protein Binding: 94% α1-acid glycoprotein

86
Q

Dibucaine
Metabolism:
MOA:

A

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

Used for dibucaine test for SCh

87
Q

What is procaine’s primary metabolite?

A

PABA

88
Q

Tetracaine metabolism is slower than ______

A

Procaine

89
Q

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

Procaine
Chloroprocaine
Tetracaine

A

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

90
Q

What is Benzocaine used for?

A

Uses: Topical anesthesia of mucous membranes:

91
Q

Overdose of Benzocaine can lead to ________.

A

OD of Benzocaine can lead to Methemoglobinemia

92
Q

What makes Benzocaine unique?

A

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

93
Q

Benzocaine
Onset:
Duration:
Dose:

A

onset: rapid

duration: 30-60 min

Dose: 200-300 mg = 20% spray

94
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

95
Q

Cocaine
Peak:
Duration:
Elimination:

A

Peak: 30-45 min
Duration: 60 min after peak
Elimination: Urine (24-36 hours)

96
Q

When should one be cautious when administering cocaine?

A

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

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