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

Lecture 16: Pharmacology of LOCAL anesthetics Flashcards

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
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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23
Q

A newly discovered local anesthetic was found to have a pKa of 7.4. What percent of anesthetic will be unionized in the plasma?

A

50% (because 50/50 = log 1 = 0)

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23
Q

A newly discovered local anesthetic was found to have a pKa of 7.4. What percent of anesthetic will be unionized in the plasma?

A

50% (because 50/50 = log 1 = 0)

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24
Q

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?

A

PABA allergy

Condoms have benzocaine

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24
Q

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?

A

PABA allergy

Condoms have benzocaine

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25
Q

Where are local anesthetics?

A

EVERYWHERE from first aid liquids, ointments, condoms

-mostly esters because ester is much easier to metabolize (avoiding toxicity)

25
Q

Where are local anesthetics?

A

EVERYWHERE from first aid liquids, ointments, condoms

-mostly esters because ester is much easier to metabolize (avoiding toxicity)

26
Q

What are the toxic effects of local anesthetics?

A

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
Q

What are the toxic effects of local anesthetics?

A

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
Q

What are the primary side effects of local toxicity?

A

Seizures
-induced because the inhibitory neurons are much more sensitive to local anesthetics than excitatory neurons
Cardiovascular toxicity (more prolonged)

27
Q

What are the primary side effects of local toxicity?

A

Seizures
-induced because the inhibitory neurons are much more sensitive to local anesthetics than excitatory neurons
Cardiovascular toxicity (more prolonged)

28
Q

What is the only exception to toxicity?

A

Bupivicaine

-cardiac dysarrhythmias are seen at subconvulsant levels

28
Q

What is the only exception to toxicity?

A

Bupivicaine

-cardiac dysarrhythmias are seen at subconvulsant levels

29
Q

How do you treat lidocaine toxicity?

A

Halt injection
If seizures occur, hyperventilate with 100% oxygen
Use benzos or thipental
Interlipids

29
Q

How do you treat lidocaine toxicity?

A

Halt injection
If seizures occur, hyperventilate with 100% oxygen
Use benzos or thipental
Interlipids

30
Q

A 38 yo woman underwent liposuction of abdmen and hips. 30 minutes following local anesthetic administration, she seized. What was the diagnosis?

A

Lidocaine toxicity

REMEMBER THE local anesthetics can be toxic

30
Q

A 38 yo woman underwent liposuction of abdmen and hips. 30 minutes following local anesthetic administration, she seized. What was the diagnosis?

A

Lidocaine toxicity

REMEMBER THE local anesthetics can be toxic

31
Q

How do you treat cardiac toxicity? Why does this make sense?

A

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
Q

How do you treat cardiac toxicity? Why does this make sense?

A

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
Q

What is intralipid? Significance?

A

It is something that increases lipid plasma concentration

Reverses local anesthesia toxicity

32
Q

What is intralipid? Significance?

A

It is something that increases lipid plasma concentration

Reverses local anesthesia toxicity

33
Q

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?

A

Intralipid

33
Q

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?

A

Intralipid

34
Q

What are the effects of local anesthetics?

A

High concentrations: Vasodilation

All local anesthetics EXCEPT for cocaine (horners)

34
Q

What are the effects of local anesthetics?

A

High concentrations: Vasodilation

All local anesthetics EXCEPT for cocaine (horners)

35
Q

An ENT surgeon would like to do a nasal endoscopy. Which local anesthetic should she use to tropicalize the nasopharynx prior to surgery?

A

A: Cocaine

Because cocaine is a vasoconstrictor, it is used when you want to limit bleeding

35
Q

An ENT surgeon would like to do a nasal endoscopy. Which local anesthetic should she use to tropicalize the nasopharynx prior to surgery?

A

A: Cocaine

Because cocaine is a vasoconstrictor, it is used when you want to limit bleeding

36
Q

What is significance of cocaine?

A

Only local anesthetic that is NOT a vasodilator

Because cocaine is a vasoconstrictor, it is used when you want to limit bleeding

36
Q

What is significance of cocaine?

A

Only local anesthetic that is NOT a vasodilator

Because cocaine is a vasoconstrictor, it is used when you want to limit bleeding

37
Q

Why are esters used for local anesthesia?

A

Because it has a smaller risk of SYSTEMIC toxicity when compared to amides

37
Q

Why are esters used for local anesthesia?

A

Because it has a smaller risk of SYSTEMIC toxicity when compared to amides

38
Q

What isomer is most effective?

A

S isomer is better

Example: Levobupivacaine

38
Q

What isomer is most effective?

A

S isomer is better

Example: Levobupivacaine

39
Q

What is the significance of prilocaine?

A

Can cause to methemoglobinemia

Because prilocaine is metabolized to alpha-orthotoludine

39
Q

What is the significance of prilocaine?

A

Can cause to methemoglobinemia

Because prilocaine is metabolized to alpha-orthotoludine

40
Q

What is Eutectic Mixture of Local Anesthetic (EMLA)?

A

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
Q

What is Eutectic Mixture of Local Anesthetic (EMLA)?

A

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
Q

What causes methemoglobinemia?

A

Prilocaine

-disease is characterized by iron isomer that has less affinity for oxygen, leading to probable hypoxia

41
Q

What causes methemoglobinemia?

A

Prilocaine

-disease is characterized by iron isomer that has less affinity for oxygen, leading to probable hypoxia

42
Q

A 30 yo woman applies EMLA cream to both legs but developed tongue numbness and cyanosis afterwards. What is diagnosis?

A

Methemoglobinemia

42
Q

A 30 yo woman applies EMLA cream to both legs but developed tongue numbness and cyanosis afterwards. What is diagnosis?

A

Methemoglobinemia

43
Q

lipid partition coefficient of lidocaine is 3 and bupivacaine is 27
Which is most potent? Shortest duration?

A

Bupivicaine because highest lipid partition coefficient

Lidocaine = shortest duration

43
Q

lipid partition coefficient of lidocaine is 3 and bupivacaine is 27
Which is most potent? Shortest duration?

A

Bupivicaine because highest lipid partition coefficient

Lidocaine = shortest duration

44
Q

What are the two key features of new class of local anesthetics?

A
  1. lipid partition coefficient (to know potency/duration)

2. pKa (so that you know how fast it brings about effect)

44
Q

What are the two key features of new class of local anesthetics?

A
  1. lipid partition coefficient (to know potency/duration)

2. pKa (so that you know how fast it brings about effect)

45
Q

During the injection of bobacaine, the patient complains of a metallic taste in the mouth. The most likely explanation is

A

Central nervous system toxicity

45
Q

During the injection of bobacaine, the patient complains of a metallic taste in the mouth. The most likely explanation is

A

Central nervous system toxicity

46
Q

If you have a metallic taste in mouth after local anesthetics

A

You have CNS Toxicity

46
Q

If you have a metallic taste in mouth after local anesthetics

A

You have CNS Toxicity

B&B Week 6 Flashcards (16 decks)

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