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B&B Week 6 Flashcards > Lecture 16: Pharmacology of LOCAL anesthetics > Flashcards

Lecture 16: Pharmacology of LOCAL anesthetics Flashcards

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1
Q

What are local anesthetics?

A

Reversibly block nerve conduction
Act on every type of nerve fiber
Act on cardiac, skeletal muscle and brain
No structural damage to nerve cell

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2
Q

What is purpose of local anesthetic?

A

To operate on awake patient without pain
To suture without pain
To do painful procedures without pain

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3
Q

What is the “ideal” local anesthetic?

A

Nonirritating to the tissue to which it is applied
Short onset
Long enough duration, but not too long as to entail a prolonged recovery period

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4
Q

What is the general overall chemical structure of local anesthetics?

A
  1. Aromatic group
  2. Intermediate group
  3. Tertiary Amine
    Weak base
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5
Q

How can you tell the difference between amides and ester anesthetics?

A

Use generic name
Two “I’s’ = amide
One “I” = ester

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6
Q

What enantiomer is the best therapeutically?

A

S for Sexy

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7
Q

Where does local anesthetic bind once it is in the blood stream?

A

Local anesthetics bind to the alpha subunit of SODIUM CHANNELS

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8
Q

What is the mechanism of local anesthetics?

A

Blocks membrane permeability to NA by crossing the membrane and
Binds to the INTERNAL membrane of the sodium channel
Binds only in the OPEN and INACTIVATED state
-so does not bind when in closed state (which makes sense)
-ionic gradient/resting membrane potential is unchanged

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9
Q

What happens when local anesthetic is injected into an acidic medium like an abscess?

A

Anesthetics are basic…so when coupled with acidic medium, it would not be able to cross the membrane

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10
Q

What effects do local anesthetics potentiate?

A
  1. Decreased the amplitude of the AP
  2. Slow the rate of depolarization
  3. Increase the firing threshold
  4. Slow impulse conduction
  5. Prolong the refractory period
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11
Q

What are the pharmokinetics of local anesthetics?

A
  1. local anesthetics bind in the blood of alpha 1-glycoprotein and albumin
  2. considerable first-pass uptake of local anesthetics by the lung
  3. local anesthetics enter the blood stream by
    • direct injection
    • absorption (epinephrine)
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12
Q

What is the significance of alpha 1-glycoprotein and albumin?

A

The proteins in blood that bind to local anesthetic

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13
Q

What is the distribution of local anesthetics

A
  1. Alpha phase = rapidly redistributed to well-perfused tissue
    • primarily goes to alpha phase
  2. Beta phase = less perfused or slowly equilibrating tissue
  3. Gamma phase = clearance representing metabolism and excretion
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14
Q

Which of the following organs is at the greatest risk of toxicity from an overdose of local anesthetic?

A

Brain

Because it is a well perfused tissue

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15
Q

Where are esters metabolized?

A

Hydrolyzed in the plasma by pseudocholinesterase
-breakdown product = para-aminobenzoicacid
Risk of ester toxicity is much les
-can lead to PABA allergy

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16
Q

What is pseudocholinesterase?

A

The enzyme in the plasma that breaks down esters

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17
Q

What is para-aminobenzoic acid (PABA)?

A

The breakdown product of esters
Can lead to ALLERGIES
PABA is an allergen

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18
Q

Where are amides metabolized?

A

Occurs in the LIVER, specifically in the ER of the hepatocytes
-tertiary amines are metabolized into secondary amines that are then hydrolyzed by amidases

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19
Q

A patient with end-stage liver disease is most susceptible to local anesthetic toxicity from which local anesthetic?

A

bupivacaine (amides)

Because amides are broken down in liver

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20
Q

What is the lipid:water partition coefficient?

A

How much more soluble a local anesthetic is in fat vs. water
The higher the coefficient, the greater the potency
E.g. bupivacaine = 27.3 and lidocaine = 2.9…so bupivacaine is more potent but slower onset

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20
Q

What is the lipid:water partition coefficient?

A

How much more soluble a local anesthetic is in fat vs. water
The higher the coefficient, the greater the potency
E.g. bupivacaine = 27.3 and lidocaine = 2.9…so bupivacaine is more potent but slower onset

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21
Q

Why do you choose lidocaine vs. bupivacaine when applying a local anesthetic prior to suturing?

A

Because lidocaine has a faster onset

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21
Q

Why do you choose lidocaine vs. bupivacaine when applying a local anesthetic prior to suturing?

A

Because lidocaine has a faster onset

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22
Q

How do you know if something has a faster response?

A

The closer to the body pH of 7.4

We want more drugs to be in the UNIONIZED form (because basic vs. acidic)

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22
How do you know if something has a faster response?
The closer to the body pH of 7.4 | We want more drugs to be in the UNIONIZED form (because basic vs. acidic)
23
A newly discovered local anesthetic was found to have a pKa of 7.4. What percent of anesthetic will be unionized in the plasma?
50% (because 50/50 = log 1 = 0)
23
A newly discovered local anesthetic was found to have a pKa of 7.4. What percent of anesthetic will be unionized in the plasma?
50% (because 50/50 = log 1 = 0)
24
A 22 yo sexually active man presented with recurrent erythmatoous-edamotous dermatitis of shaft of penis. He uses condoms for birth control. What is diagnosis?
PABA allergy | Condoms have benzocaine
24
A 22 yo sexually active man presented with recurrent erythmatoous-edamotous dermatitis of shaft of penis. He uses condoms for birth control. What is diagnosis?
PABA allergy | Condoms have benzocaine
25
Where are local anesthetics?
EVERYWHERE from first aid liquids, ointments, condoms | -mostly esters because ester is much easier to metabolize (avoiding toxicity)
25
Where are local anesthetics?
EVERYWHERE from first aid liquids, ointments, condoms | -mostly esters because ester is much easier to metabolize (avoiding toxicity)
26
What are the toxic effects of local anesthetics?
Starts with numbness, lightheadedness, and Visual disturbance Evolves into Muscular twitching, unconsciousness, coma, respiratory arrest, CVS depression Cardiotoxicity includes -interference with contractility and automaticity -ventricular arrhythmias
26
What are the toxic effects of local anesthetics?
Starts with numbness, lightheadedness, and Visual disturbance Evolves into Muscular twitching, unconsciousness, coma, respiratory arrest, CVS depression Cardiotoxicity includes -interference with contractility and automaticity -ventricular arrhythmias
27
What are the primary side effects of local toxicity?
Seizures -induced because the inhibitory neurons are much more sensitive to local anesthetics than excitatory neurons Cardiovascular toxicity (more prolonged)
27
What are the primary side effects of local toxicity?
Seizures -induced because the inhibitory neurons are much more sensitive to local anesthetics than excitatory neurons Cardiovascular toxicity (more prolonged)
28
What is the only exception to toxicity?
Bupivicaine | -cardiac dysarrhythmias are seen at subconvulsant levels
28
What is the only exception to toxicity?
Bupivicaine | -cardiac dysarrhythmias are seen at subconvulsant levels
29
How do you treat lidocaine toxicity?
Halt injection If seizures occur, hyperventilate with 100% oxygen Use benzos or thipental Interlipids
29
How do you treat lidocaine toxicity?
Halt injection If seizures occur, hyperventilate with 100% oxygen Use benzos or thipental Interlipids
30
A 38 yo woman underwent liposuction of abdmen and hips. 30 minutes following local anesthetic administration, she seized. What was the diagnosis?
Lidocaine toxicity | REMEMBER THE local anesthetics can be toxic
30
A 38 yo woman underwent liposuction of abdmen and hips. 30 minutes following local anesthetic administration, she seized. What was the diagnosis?
Lidocaine toxicity | REMEMBER THE local anesthetics can be toxic
31
How do you treat cardiac toxicity? Why does this make sense?
Add lipids into the blood Because anesthetics are much more soluble in lipids Lipids will take those local anesthetics out of blood and will be instead carried in the lipids
31
How do you treat cardiac toxicity? Why does this make sense?
Add lipids into the blood Because anesthetics are much more soluble in lipids Lipids will take those local anesthetics out of blood and will be instead carried in the lipids
32
What is intralipid? Significance?
It is something that increases lipid plasma concentration | Reverses local anesthesia toxicity
32
What is intralipid? Significance?
It is something that increases lipid plasma concentration | Reverses local anesthesia toxicity
33
91-year old man received a block for arm surgery. Following injection of 30 ml mepivicaine, he became unresponsive and developed bigeminy. Which medication should he receive?
Intralipid
33
91-year old man received a block for arm surgery. Following injection of 30 ml mepivicaine, he became unresponsive and developed bigeminy. Which medication should he receive?
Intralipid
34
What are the effects of local anesthetics?
High concentrations: Vasodilation | All local anesthetics EXCEPT for cocaine (horners)
34
What are the effects of local anesthetics?
High concentrations: Vasodilation | All local anesthetics EXCEPT for cocaine (horners)
35
An ENT surgeon would like to do a nasal endoscopy. Which local anesthetic should she use to tropicalize the nasopharynx prior to surgery?
A: Cocaine | Because cocaine is a vasoconstrictor, it is used when you want to limit bleeding
35
An ENT surgeon would like to do a nasal endoscopy. Which local anesthetic should she use to tropicalize the nasopharynx prior to surgery?
A: Cocaine | Because cocaine is a vasoconstrictor, it is used when you want to limit bleeding
36
What is significance of cocaine?
Only local anesthetic that is NOT a vasodilator | Because cocaine is a vasoconstrictor, it is used when you want to limit bleeding
36
What is significance of cocaine?
Only local anesthetic that is NOT a vasodilator | Because cocaine is a vasoconstrictor, it is used when you want to limit bleeding
37
Why are esters used for local anesthesia?
Because it has a smaller risk of SYSTEMIC toxicity when compared to amides
37
Why are esters used for local anesthesia?
Because it has a smaller risk of SYSTEMIC toxicity when compared to amides
38
What isomer is most effective?
S isomer is better | Example: Levobupivacaine
38
What isomer is most effective?
S isomer is better | Example: Levobupivacaine
39
What is the significance of prilocaine?
Can cause to methemoglobinemia | Because prilocaine is metabolized to alpha-orthotoludine
39
What is the significance of prilocaine?
Can cause to methemoglobinemia | Because prilocaine is metabolized to alpha-orthotoludine
40
What is Eutectic Mixture of Local Anesthetic (EMLA)?
A cream (used in pediatrics) Contains lidocaine, prilocaine, emulsifier, thickener, distilled water -must be applied one hour prior to procedure PRILOCAINE cane lead to METHEMOGLOBINEMIA
40
What is Eutectic Mixture of Local Anesthetic (EMLA)?
A cream (used in pediatrics) Contains lidocaine, prilocaine, emulsifier, thickener, distilled water -must be applied one hour prior to procedure PRILOCAINE cane lead to METHEMOGLOBINEMIA
41
What causes methemoglobinemia?
Prilocaine | -disease is characterized by iron isomer that has less affinity for oxygen, leading to probable hypoxia
41
What causes methemoglobinemia?
Prilocaine | -disease is characterized by iron isomer that has less affinity for oxygen, leading to probable hypoxia
42
A 30 yo woman applies EMLA cream to both legs but developed tongue numbness and cyanosis afterwards. What is diagnosis?
Methemoglobinemia
42
A 30 yo woman applies EMLA cream to both legs but developed tongue numbness and cyanosis afterwards. What is diagnosis?
Methemoglobinemia
43
lipid partition coefficient of lidocaine is 3 and bupivacaine is 27 Which is most potent? Shortest duration?
Bupivicaine because highest lipid partition coefficient | Lidocaine = shortest duration
43
lipid partition coefficient of lidocaine is 3 and bupivacaine is 27 Which is most potent? Shortest duration?
Bupivicaine because highest lipid partition coefficient | Lidocaine = shortest duration
44
What are the two key features of new class of local anesthetics?
1. lipid partition coefficient (to know potency/duration) | 2. pKa (so that you know how fast it brings about effect)
44
What are the two key features of new class of local anesthetics?
1. lipid partition coefficient (to know potency/duration) | 2. pKa (so that you know how fast it brings about effect)
45
During the injection of bobacaine, the patient complains of a metallic taste in the mouth. The most likely explanation is
Central nervous system toxicity
45
During the injection of bobacaine, the patient complains of a metallic taste in the mouth. The most likely explanation is
Central nervous system toxicity
46
If you have a metallic taste in mouth after local anesthetics
You have CNS Toxicity
46
If you have a metallic taste in mouth after local anesthetics
You have CNS Toxicity

B&B Week 6 Flashcards (16 decks)

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