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Anesthesia Pharmacology (Spring 2025) > Lecture 16 (Exam 4 Local Anesthetics Part I) > Flashcards

Lecture 16 (Exam 4 Local Anesthetics Part I) Flashcards

1
Q

What was the first local anesthetic?

A

Cocaine

Cocaine is an ester.

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2
Q

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

A

Ophthalmology (1884)

Local vasoconstriction: shrink nasal mucosa.

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3
Q

What was the first synthetic ester developed in 1905?

A

Procaine

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4
Q

What was the first synthetic amide developed in 1943?

A

Lidocaine

Gold Standard

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5
Q

What are the uses Local Anesthetics (LAs)?

A
  • Treat dysrhythmias
  • Analgesia: Acute and chronic pain
  • Anesthesia- ANS Blockade, Sensory Anesthesia, Skeletal Muscle Paralysis
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6
Q

What antiarrhythmic Drug Class is lidocaine in?

A

Class I: Sodium Channel Blockers

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7
Q

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

A

1 mg/kg over an hour

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8
Q

MAGA:
What is the IV dose of Lidocaine?

When should lidocaine be terminated?

A
  • 1 to 2 mg/kg IV (initial bolus) over 2 - 4 min.
  • 1 to 2 mg/kg/hour (drip)
  • terminated 12 - 72 hours
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9
Q

What are considerations of lidocaine?

A

Careful monitoring: cardiac, hepatic, renal dysfunction

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10
Q

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

A

Analgesia

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11
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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12
Q

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

A
  • Seizures
  • Unconsciousness
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13
Q

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

A
  • Apnea
  • Coma
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14
Q

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

A
  • Cardiovascular Depression
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15
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.

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16
Q

Composition of LA will have a pH of _____ and are weak _______. ?

A

pH of 6; weak bases

A majority of LA are weak bases

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17
Q

Procaine
Classification:
Potency:
Onset:
Duration after infiltration (min):
Max single dose for infiltration (mg):
pK:
Protein Binding (%):

A

Procaine
Classification: Ester
Potency: 1
Onset: Slow
Duration after infiltration (min): 45-60
Max single dose for infiltration (mg): 500
pK: 8.9
Protein Binding (%): 6

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18
Q

Chloroprocaine
Classification:
Potency:
Onset:
Duration after infiltration (min):
Max single dose for infiltration:
pK:

A

Chloroprocaine
Classification: Ester
Potency: 4
Onset: Rapid
Duration after infiltration (min): 30-45
Max single dose for infiltration (mg): 600
pK: 8.7

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19
Q

Tetracaine
Classification:
Potency:
Onset:
Duration after infiltration (min):
Max single dose for infiltration:
pK:
Protein Binding (%):

A

Tetracaine
Classification: Ester
Potency: 16
Onset: Slow
Duration after infiltration (min): 60-180
Max single dose for infiltration (mg): 100 (topical)
pK: 8.5
Protein Binding (%): 76

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20
Q

Lidocaine
Classification:
Potency:
Onset:
Duration after infiltration (min):
Max single dose for infiltration:
Toxic Plasma Concentration (mcg/mL)
pK:
Protein Binding (%):

A

Lidocaine
Classification: Amide
Potency: 1
Onset: Rapid
Duration after infiltration (min): 60-120
Max single dose for infiltration (mg): 300
Toxic Plasma Concentration (mcg/mL): >5
pK: 7.9
Protein Binding (%): 70

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21
Q

Prilocaine
Classification:
Potency:
Onset:
Duration after infiltration (min):
Max single dose for infiltration:
Toxic Plasma Concentration (mcg/mL)
pK:
Protein Binding (%):

A

Prilocaine
Classification: Amide
Potency: 1
Onset: Slow
Duration after infiltration (min): 60-120
Max single dose for infiltration (mg): 400
Toxic Plasma Concentration (mcg/mL): >5
pK: 7.9
Protein Binding (%): 55

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22
Q

Mepivacaine
Classification:
Potency:
Onset:
Duration after infiltration (min):
Max single dose for infiltration:
Toxic Plasma Concentration (mcg/mL)
pK:
Protein Binding (%):

A

Mepivacaine
Classification: Amide
Potency: 1
Onset: Slow
Duration after infiltration (min): 90-180
Max single dose for infiltration (mg): 300
Toxic Plasma Concentration (mcg/mL): >5
pK: 7.6
Protein Binding (%): 77

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23
Q

Bupivacaine
Classification:
Potency:
Onset:
Duration after infiltration (min):
Max single dose for infiltration:
Toxic Plasma Concentration (mcg/mL)
pK:
Protein Binding (%):

A

Bupivacaine
Classification: Amide
Potency: 4
Onset: Slow
Duration after infiltration (min): 240-480
Max single dose for infiltration (mg): 175
Toxic Plasma Concentration (mcg/mL): >3
pK: 8.1
Protein Binding (%): 95

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24
Q

Levobupivacaine
Classification:
Potency:
Onset:
Duration after infiltration (min):
Max single dose for infiltration:
pK:
Protein Binding (%):

A

Levobupivacaine
Classification: Amide
Potency: 4
Onset: Slow
Duration after infiltration (min): 240-480
Max single dose for infiltration: 175
pK: 8.1
Protein Binding (%): >97

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25
**Ropivacaine** Classification: Potency: Onset: Duration after infiltration (min): Max single dose for infiltration: Toxic Plasma Concentration (mcg/mL) pK: Protein Binding (%):
**Ropivacaine** Classification: Amide Potency: 4 Onset: Slow Duration after infiltration (min): 240-480 Max single dose for infiltration (mg): 200 Toxic Plasma Concentration (mcg/mL): >4 pK: 8.1 Protein Binding (%): 94
26
Which LA will have a potency of 16?
Tetracaine
27
Which LAs will have a potency of 4?
Chloroprocaine Bupivacaine Levobupivacaine Ropivacaine
28
Which LAs will have rapid onset?
Chloroprocaine Lidocaine
29
Which 3 LA will have the highest protein binding?
Levobupivacaine (>97%) Bupivacaine (95%) Ropivacaine (94%)
30
Lipid solubility correlates to _______ of the drug. Which LA has the highest lipid solubility?
potency Tetracaine
31
What are Liposomes used for?
* Used to upload a higher amount of LA into a molecule & have a consistent release of LA in the tissues. * Prolonged duration of action & decreased toxicity
32
FDA released what LA drug that contains liposomes and can last up to 96 hours.
Bupivacaine ER (Exparel)
33
MOA of Local Anesthetics
* 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 black the Na+ gated channel from within the cell.*
34
Factors affecting LA blockade.
* Lipid solubility or non-ionized form * Repetitively stimulated nerve (↑ sensitivity) * Diameter of the nerve (↑ diameter, ↑ LA)
35
What happens when you expose LA (a weak base) to an acidic environment?
LA becomes ionized. When LA becomes ionized, it will not cross cell membrane to block Na+ gated channels.
36
What targets/channels can be modulated to make LA work better?
* Potassium channels * Calcium Ion Channels * G protein-coupled receptors
37
Minimum Effective Concentration or Cm (LAs) = _________ (Volatile Agents)
MAC
38
What component of the local anesthetic is required for the conduction block?
Non-ionized form (equates with lipid solubility)
39
Larger fibers need _____ concentrations of LAs.
higher
40
The diameter of the motor nerve is how many times larger than the diameter of the sensory nerve.
Twice as large in diameter
41
How many nodes of Ranvier need to be blocked to equate to 1 cm of local anesthesia?
At least 2, preferably 3 Nodes of Ranvier to prevent the conduction (Minimum Effect Concentration)
42
If LA were given intravascularly, which fibers would be affected the fastest? What signs and symptoms would you see?
Pre-ganglionic B fibers (SNS) Hypotension and bradycardia
43
What fibers are blocked if the patient can't tell if they are being poked by a sharp needle?
* Myelinated A and B fibers
44
What is typically affected last when administering LA through the epidural/spinal? What fibers are the last to be affected?
* Motor * Myelinated A-δ and unmyelinated C-fibers
45
Which patient population will have increased sensitivity and be harder to block?
Pregnancy
46
Pharmacokinetics of LA If pKa is close to physiological pH, how does this affect the onset of action?
Faster onset
47
When administering LA, only ______% of the drug is in lipid-soluble nonionized form.
50%
48
If a LA has good vasodilator activity, what happens to its potency? What happens to the duration of action?
LA is less potent ↓ Duration of action
49
Because Lidocaine has vasodilator activity, there is (greater/less) _______ systemic absorption. Resulting in a (shorter/longer) ________ duration of action.
greater shorter
50
Factors that influence the absorption of LA.
* Site of injection * Dosage * Epinephrine will prolong the duration of action (limit systemic absorption of LA by one-third). * Pharmacologic characteristics of the drug
51
List the uptake of Local Anesthetics Based on Regional Anesthesia Technique from highest blood concentration to lowest blood conc.
52
________is the primary determinant of potency
Lipid solubility
53
The rate of clearance is dependent on what two factors?
* Cardiac output * Protein binding: % bound is inversely related to % plasma. (*40% albumin-bound means 60% will float freely in plasma.*)
54
Which LA will metabolize the fastest?
Chloroprocaine d/t the 0% of protein binding.
55
Which LA will metabolize the slowest?
Levobupivacaine d/t the highest % of protein binding.
56
Why is it important to know the metabolizing rate of LA.
Re-dosing of LA
57
Metabolism of Amides. Location of Metabolism: Rapid: Intermediate: Slow:
Metabolism of Amides. Location of Metabolism: Microsomal enzyme (Liver) Rapid: Prilocaine Intermediate: Lidocaine, Mepivacaine Slow: Etidocaine, Bupivacaine, Ropivacaine
58
Metabolism of Esterase
Hydrolyzed by hydrocholinesterases in plasma, except cocaine which is metabolized by the liver.
59
What is the metabolite of esters? What is the significance of this metabolite?
ParaAminoBenzoic acid (PABA) Allergies
60
Is there cross-sensitivity between an amide allergy to an ester allergy?
No
61
Which class of LA has a slower metabolism
Amides are slower at metabolism.
62
What are the most common LAs that have first-pass pulmonary extraction?
* Lidocaine * Bupivacaine (dose dependent) * Prilocaine
63
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.
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.
64
In general, the more lipid soluble the local anesthetic is, the greater the potency. T/F
True
65
Which local anesthetic property is most important regarding the duration of action?
**Lipid Solubility** (most important)
66
Pharmacokinetics: Pregnancy Plasma cholinesterases levels
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.*
67
What classification of LAs is more likely to cause ion trapping?
Amides *Ion trapping will lead to LA toxicity in the placenta.*
68
What is ion trapping?
The pH in the fetal environment is more acidic than in maternal circulation. LA becomes ionized and trapped in the fetal circulation.
69
If there is ion trapping in the placenta, what can be given to adjust the pH?
Sodium Bicarb
70
**Bupivacaine** Protein Bound: Arterial Concentration:
**Bupivacaine** Protein Bound: 95% Arterial Concentration: 0.32
71
**Lidocaine** Protein Bound : Arterial Concentration:
**Lidocaine** Protein Bound: 70% Arterial Concentration: 0.73
72
**Prilocaine** % Protein Bound Arterial Concentration
**Prilocaine** Protein Bound: 55% Arterial Concentration: 0.85
73
Lidocaine Metabolite: What will affect metabolism and elimination:
Lidocaine Metabolite: Xylidide What will affect metabolism and elimination: Hepatic disease
74
What is Lidocaine max infiltration dose (plain and w/ epi)?
Maximum infiltration dose: **300 mg plain** **500 mg with EPI** (*Rate of distribution is slower with epinephrine, so we can give more lidocaine.*)
75
How will Pregnancy Induced Hypertension affect lidocaine clearance?
Prolong clearance
76
Prilocaine metabolite. What is the issue with this metabolite?
Metabolite: Orthotoluidine The metabolite converts Hemoglobin to Methemoglobin, resulting in Methemoglobinemia.
77
What is the result of Methemoglobinemia?
Fe3+ (ferric iron) is not capable of carrying O2
78
Max dose of prilocaine
600 mgs
79
Signs and sx of Prilocaine induced methemoglobinemia Tx:
S/Sx: Cyanosis d/t decreased 02 carrying capacity Methylene Blue 1 to 2 mg/kg IV over 5 mins (initial dose) Max dose: 7 to 8 mg/kg (over 24 hours)
80
Mepivacaine is similar to Lidocaine except:
* Longer duration of action * Lacks vasodilator activity * Prolonged elimination in fetus & newborn * No Mepivacaine in OB patients
81
What is bupivacaine bound to?
95% bound to α1-Acid glycoprotein
82
Ropivacaine Metabolism: Metabolite: Protein Binding
Ropivacaine Metabolism: Hepatic cytochrome P450 enzymes Metabolites: Can accumulate with uremic patients Lesser system toxicity than Bupivacaine Protein Binding: 94% bound to α1-acid glycoprotein
83
Dibucaine Metabolism: Enzyme Inhibition:
Dibucaine Metabolism: Liver Enzyme Inhibition: inhibits the activity of normal butyrylcholinesterase (plasma cholinesterase) by more than 70% *This LA is used to test for atypical plasma cholinesterase.*
84
Procaine Metabolite:
Procaine Metabolite: **PABA** (ester anesthetic), excreted unchanged in the urine
85
Chloroprocaine metabolizes ______ times faster than Procaine. Pregnancy decreases plasma cholinesterase by ____%
* 3.5x faster than procaine * 40%
86
Which ester LA has the slowest metabolism?
Tetracaine d/t 76% protein bound
87
Which LA will have the highest rate of metabolism? Procaine Chloroprocaine Tetracaine
* Chloroprocaine (fastest metabolism, 0% protein bound) * Procaine (6% protein bound) * Tetracaine (slowest, 76% protein bound)
88
Benzocaine use:
Uses: Topical anesthesia of mucous membranes: Tracheal intubation, Endoscopy, Transesophageal echocardiography (TEE), Bronchoscopy *Benzocaine comes in a spray.*
89
Benzocaine Onset: Duration: Dose: Brief spray (20%) = Overdose of Benzocaine can lead to ________.
Benzocaine Onset: Rapid Duration: 30 to 60 minutes Dose: Brief spray (20% concentration) = 200 to 300 mgs OD of Benzocaine can lead to **Methemoglobinemia**
90
What makes Benzocaine unique?
Weak acid instead of a weak base, like most LA. pKa = 3.5
91
How is cocaine metabolized? Who should receive decreased amounts of cocaine?
Metabolized by plasma and liver cholinesterase Decrease cocaine use in parturients, neonates, the elderly, and severe hepatic disease
92
Cocaine Peak: Duration: Elimination:
Cocaine Peak: 30 to 45 mins Duration: 60 minutes after peak Elimination: Urine (24 to 36 hours)
93
Adverse side effects of cocaine.
Cocaine is a stimulant; use it with caution. Cocaine can cause coronary vasospasm, ventricular dysrhythmias, HTN, tachycardia, and CAD.

Anesthesia Pharmacology (Spring 2025) (20 decks)

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