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24 Anesthesia Pharm > 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

Gold Standard “(cocaine) but lidocaine is referred most”

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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
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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?

A
  • 1 to 2 mg/kg IV (initial bolus) over 2 - 4 min.
  • 1 to 2 mg/kg/hour (drip) terminated at 12-72 hours
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10
Q

When should lidocaine be terminated?

A
  • Terminate within 12 - 72 hours
  • Monitoring: cardiac, hepatic, renal dysfunction
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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 lidocaine.

A

Lipophilic Portion (Aromatic Section)
Hydrocarbon Chain amide
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 hydrophilic chain will determine if LA is an ester or an amide.

AKA Hydrocarbon/intermediate chain

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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 hydrophilic 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 pK of _____ and are weak _______. ?

A

pK of 8 (above physiological pH); weak bases

A majority of LA are weak bases

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21
Q

Increased potency generally correlates to increased __________.

A

lipid solubility

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22
Q

Which ester is the most potent?

A

Tetracaine
- potency 16
- lipid solubility 80

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23
Q

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

A
  • Bupivacaine 95%
  • Levobupivacaine >97%
  • Ropivacaine 94%
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24
Q

Which two local anesthetics will have the most rapid onset?

A

Ester - Chloroprocaine
Amide - Lidocaine

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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

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

A

Physiological pH (7.35 - 7.45)

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27
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)
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28
Q

Which ester has the greatest degree of lipid solubility?

A

Tetracaine at 80!

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29
Q

Which amide has the greatest degree of lipid solubility?

A

Bupivacaine at 28

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30
Q

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

A
  • uploads higher amount of LA’s into a molecule (liposomes) & have a consistent/control release of LA in the tissue
  • Prolonged duration of action & decreased toxicity

Bupivacaine ER (Exparel) up to 96 hr!

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31
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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32
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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33
Q

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

A

Becoming water-soluble and ionized.

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34
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)
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35
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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36
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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37
Q

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

A

MAC

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38
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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39
Q

Larger fibers need _____ concentrations of LAs.

A

higher

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40
Q

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

A

2x
BOOK “The Cm of motor fibers is approximately twice that of sensory fibers; thus, sensory anesthesia may not always be accompanied by skeletal muscle paralysis.”

41
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)

42
Q

If a LA were given via spinal or intravascular, which fibers would be affected the fastest?

What signs and symptoms would you see?

A

Pre-ganglionic B fibers (SNS)

Hypotension and ?bradycardia?
Reflex Tachycardia

43
Q

What fibers are blocked if the patient can’t feel pain or temperature?

A
  • Myelinated A and B fibers???
    (Myelinated A-delta and unmyelinated C fibers)
44
Q

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

What sensations are the last to be affected?

A
  • motor fibers are last to be block
  • touch/pressure (A-beta), proprioception (A-alpha) and Motor (A-alpha/gamma)
45
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 (these should be block second. Pain and temperature fibers)
46
Q

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

A

Pregnancy

Harder or easier? lol

47
Q

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

A

more

48
Q

Because the pKA of LA’s are 8, less than ______% of the drug is in lipid-soluble nonionized form in physiological pH of 7.4.

A

50%

49
Q

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

What happens to the duration of action?

A

LA is less potent? (Won’t stay on intended site)

↓ Duration of action at the local site injected

50
Q

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

A

greater

51
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
52
Q

Factors that influence the absorption of LA.

A
  • Site of injection
  • Dosage
  • Epinephrine use
  • Pharmacologic characteristics of the drug
53
Q

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

A
54
Q

________is the primary determinant of potency

A

Lipid solubility

55
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.)

56
Q

Which LA will metabolize the fastest?

A

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

  • Chloroprocaine E1/2 = 7min, DOA 30-45 min
  • Procaine E1/2 = 9 min, 6% PB, DOA 45-60min
57
Q

Which amides will metabolize the slowest?

A
  • Bupivacaine 95% PB
  • Levobupivacaine > 97% PB
  • Ropivacaine 94% PB

Most rapid Prilocaine only 55% PB

58
Q

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

A

Re-dosing of LA

59
Q

Where are Amide local anesthetics metabolized?

A

Liver via CYP 450’s

60
Q

Which Amide is most rapidly metabolized?

A

Prilocaine (lowest protein binding 55%)

61
Q

Which Amides exhibit intermediate metabolism?

A
  • Lidocaine PB 70%
  • Mepivacaine PB 77%
62
Q

Which Amides exhibit the slowest metabolism?

A
  • Bupivacaine 95% PB
  • Ropivacaine 94% PB
    (Levobupivacaine >97% PB?)
63
Q

How are esters metabolized?

A

Hydrolyzed by cholinesterases in plasma

64
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

65
Q

What is the metabolite of esters?

What is the significance of this metabolite?

A
  • ParaAminoBenzoic acid (PABA)
  • Common cause of Allergies
66
Q

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

A

No

67
Q

Are amides or esters, generally slower at metabolizing?

A

Amides are slower at metabolism.

(CYP450s instead of plasma cholinesterases)

68
Q

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

A
  • Lidocaine
  • Bupivacaine (dose dependent)
  • Prilocaine
69
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.

70
Q

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

A

True

71
Q

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

A

protein binding (most important)

72
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.

73
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.

74
Q

What is ion trapping?

A

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

75
Q

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

A

Sodium Bicarb

76
Q

Bupivacaine
Protein Bound:
Arterial Concentration:

A

Bupivacaine
Protein Bound: 95%
Arterial Concentration: 0.32

77
Q

Lidocaine
Protein Bound :
Arterial Concentration:

A

Lidocaine
Protein Bound: 70%
Arterial Concentration: 0.73

78
Q

Prilocaine
Protein Bound:
Arterial Concentration:

A

Prilocaine
Protein Bound: 55%
Arterial Concentration: 0.85

79
Q

What is the major metabolite of lidocaine?

A

Xylidide

Metabolism: oxidative dealkylation in liver then hydrolysis

80
Q

What is Lidocaine’s max infiltration dose?

A
  • 300 mg solo
  • 500 mg with epi
81
Q

Lidocaine will have prolonged clearance with ______

A

Pregnancy Induced Hypertension (impaired blood flow to liver, HELLP syndrome)

82
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.

83
Q

What is the result of Methemoglobinemia?

A

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

Cyanosis

84
Q

What is the max dose of prilocaine?

A

600 mgs (only given solo)

85
Q

What is the treatment for methemoglobinemia secondary to prilocaine or benzocaine overdose?

A

Methylene Blue

  • 1 to 2 mg/kg IV over 5 mins (initial dose)
  • Total dose not to exceed 7 to 8 mg/kg (over 24 hours?)
86
Q

Mepivacaine is similar to Lidocaine except:

A
  • Longer duration of action 90-180min, PB 77% (lidocaine DOA 60-180 min, PB 70%)
  • Lacks vasodilator activity
  • prolong elimination in fetuses & newborn; NO OB
87
Q

Can Mepivacaine be given in pregnant patients?

A

No. Prolonged elimination in fetus & newborn
- prolong duration of action 90-180min
- PB 77%

88
Q

What plasma protein does Bupivacaine bind to?

A

95% bound to α1-Acid glycoprotein

89
Q

Ropivacaine

Metabolism:
Metabolite:
Systemic toxicity:
Protein Binding:

A
  • Metabolism: Hepatic cytochrome P450 enzymes
  • Metabolites: Can accumulate with uremic patients
  • Lesser system toxicity than Bupivacaine (>4 mcg/mL plasma)
  • Protein Binding: α1-acid glycoprotein 94%
90
Q

Dibucaine
Metabolism:
MOA:

A

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

91
Q

What is procaine’s primary metabolite?

A

PABA

92
Q

Tetracaine metabolism is slower than ______

A

Procaine

Hydrolysis: chloroprocain > procaine > tetracaine

93
Q

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

Procaine
Chloroprocaine
Tetracaine

A

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

94
Q

What is Benzocaine used for?

A

Uses: Topical anesthesia of mucous membranes - tracheal intubation, endoscopy, TEE, bronchoscopy

  • OOA: rapid
  • DOA: 30-60 minutes
  • Dose: brief spray (20%) = 200-300mg
95
Q

Overdose of Benzocaine can lead to ________.

A

OD of Benzocaine can lead to Methemoglobinemia

96
Q

What makes Benzocaine unique?

A

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

97
Q

How is cocaine metabolized?

Who should receive decreased amounts of cocaine?

Peak, DOA & elimination?

A

Metabolized by liver cholinesterase > plasma cholinesterase

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

Peak 30 to 45 min
Duration 60 min after peak
Elimination by urine (24 to 36 hr)

98
Q

When should one be cautious when administering cocaine?

A

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

24 Anesthesia Pharm (20 decks)

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