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Apex Review > Local anesthetics 2 > Flashcards

Local anesthetics 2 Flashcards

1
Q

Select the true statement regarding the primary mechanism of action of local anesthetics.
a. the conjugate acid binds to the extracellular portion of the sodium channel
b. the conjugate acid binds to the intracellular portion of the sodium channel
c. the uncharged base binds to the extracellular portion of the sodium channel
d. the uncharged base binds to the intracellular portion of the sodium channels

A

b. conjugate acid binds to the intracellular portion of the sodium channel

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2
Q

Local anesthetics are

A

weak bases

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3
Q

After you inject local anesthetic around a nerve, the local anesthetic rapidly

A

dissociates into an uncharged base (LA) and an ionized conjugate acid (LA+)

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4
Q

Since local anesthetics are weak bases with pKa values higher than 7.4, we can predict that

A

> 50% of the local anesthetic will exist as the ionized, conjugate acid

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5
Q

Only ________- binds to the local anesthetic binding site

A

ionized, conjugate acid

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6
Q

The sodium channel remains in the closed, inactivated state until

A

enough local anesthetic diffuses away; during this time it’s resistant to depolariziation

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7
Q

Some of the non-ionized local anesthetic molecules diffuse thorugh

A

the lipid-rich axolemma
once inside, a new equilibrium between LA and La+ is established ;

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8
Q

What 3 paths can a local anesthetic travel after it’s injected near a peripheral nerve?

A
  1. diffuse into the nerve
  2. diffuse into surrounding tissue and bind to neighboring proteins
  3. diffuse into the systemic circulation
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9
Q

A patient states she experienced hypotension, tachycardia, and shortness of breath after receiving tetracaine during a previous surgery. Which drugs should be avoided in this patient? (select 3)
a. benzocaine
b. chloroprocaine
c. EMLA cream
d. articaine
e. cocaine
f. mepivacaine

A

a. benzocaine
b. chloroprocaine
e. cocaine

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10
Q

What are the two classes of local anesthetics?

A

esters & amides

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11
Q

The local anesthetic molecule is constructed from three key components:

A

benzene ring
intermediate side chain
tertiary amine

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12
Q

__________determines the local anesthetic’s drug class

A

the intermediate side chain

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13
Q

The intermediate side chain determines how

A

each drug class is metabolized

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14
Q

Amide-type local anesthetics are metabolized

A

in the liver by the P450 system

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15
Q

Ester- type local anesthetics are metabolized

A

in the plasma by pseudocholinesterase

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16
Q

What are the ester-type local anesthetics?

A

benzocaine
cocaine
chloroprocaine
procaine
tetracaine

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17
Q

What are the amide-type local anesthetics?

A

bupivacaine
dibucaine
lidocaine
mepivacaine
ropivacaine

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18
Q

All the amides have

A

two “i’s” in their names

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19
Q

Although true allergy to local anesthetics is rare, it is more common with

A

esters due to PABA

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20
Q

If a patient has experienced a true allergy with an ester, the safest course is to

A

change to a preservative free amide

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21
Q

Is there cross sensitivity between esters and amides?

A

no

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22
Q

What is PABA?

A

para-aminobenzoic acid
can be found in ester LA

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23
Q

Which characteristics correlate BEST with local anesthetic duration of action?
a. protein binding
b. lipid solubility
c. pKa
d. concentration

A

a. protein binding

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24
Q

What is the primary determinant of onset of action with LAs?

A

pKa

25
Q

What is the secondary determinants of onset of action with LAs?

A

dose and concentration

26
Q

What is the primary determinant of potency with LAs?

A

lipid solubility

27
Q

What are the secondary determinants of potency with LAs?

A

intrinsic dilating effects

28
Q

What is the primary determinant of duration of action?

A

plasma protein binding

29
Q

What is the secondary determinants of duration of action?

A

lipid solubility & addition of vasoconstrictors

30
Q

If the pKa of the local anesthetic is closer to the pH of the blood, then a larger fraction of molecules will exist as

A

the lipid-soluble uncharged base. More molecules diffusing across the axolemma translates to a faster onset of action

31
Q

If the pKa of the LA is further away from the pH of the blood, there will be

A

fewer molecules available to penetrate the cell membrane which prolongs the onset of action

32
Q

Explain why chloroprocaine is exception to the pKa & onset of action.

A

chloroprocaine has a high pKa in isolation this would suggest a slower onset; it is not very potent so large dose must be given creating a mass effect that has a rapid onset of action

33
Q

Agents that are more liphophilic tend to be

A

more potent and have longer durations of action

34
Q

Lipid solubility is increased with

A

alkyl group substitution on the amide group and the benzene ring

35
Q

At higher concentrations (what we clinically use), LAs cause

A

vasodilation which removes the LA from its site of action and contributes to the termination of its effect

36
Q

_________ is an exception to vasodilation because it inhibits NE reuptake and always causes vasoconstriction

A

cocaine

37
Q

The pKA correlates with

A

the onset of action

38
Q

The closer the pKa is to the pH of the blood, the ___________ the local anesthetic begins to take effect.

A

faster

39
Q

Is a local anesthetic an acid or a base?

A

weak base

40
Q

If you put a local anesthetic in an aqueous solution, a fraction

A

will remain non-ionized and the remaining fraction will ionize

41
Q

When the drug’s pKa is closer to blood pH, then there’s a higher amount of

A

uncharged base
there’s more drug that can diffuse through the axolemma

42
Q

What is the pKa of bupivacaine?

A

8.1

43
Q

What is the pKa of levobupivacaine?

A

8.1

44
Q

What is the pKa of ropivacaine?

A

8.1

45
Q

What is the pKa of lidocaine?

A

7.9

46
Q

What is the pKa of prilocaine?

A

7.9

47
Q

What is the pKa of mepivacaine?

A

7.6

48
Q

What is the pKa of procaine?

A

8.9

49
Q

What is the pKa of chloroprocaine?

A

8.7

50
Q

What is the pKa of tetracaine?

A

8.5

51
Q

_______________ does not undergo protein binding.

A

chloroprocaine

52
Q

The exception to the rule of the closer the pKa is to the pH of the blood, the faster the onset is

A

chloroprocaine

53
Q

All ester local anesthetics have __________ pKa values

A

higher (8.5-8.9)

54
Q

All amides have _________________ pKa values

A

lower (than the esters… highest is 8.1)

55
Q

What is the pH of benzocaine?

A

3.5

56
Q

The only local anesthetic with a pKa well below physiologic pH is

A

benzocaine

57
Q

With benzocaine, ____________________ is a significant risk

A

methemoglobinemia

58
Q

Benzocaine is useful for

A

topical anesthesia of mucus membranes during endoscopy, TEE placement, and bronchoscopy

59
Q

In an acidic solution, weak bases are:

A

more ionized and water soluble

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