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PHAR 341 - Pharmacology > Local Anesthetics > Flashcards

Local Anesthetics Flashcards

1
Q

Pain Pathways consists of:

A
  1. Pain receptors (nociceptors) located in tissue
  2. Peripheral nerves (along which the signal travels)
  3. Brainstem (cranial nerves) or spinal cord (body)
  4. Thalmus
  5. Cortex
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2
Q

types of tissue damage or trauma

A
  1. mechanical (cut or bruise)
  2. thermal (sun burn)
  3. chemical (alcohol on cut)
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3
Q

Order of lost of fxn caused by local anesthetics

A
  1. Temperature/Pain (small fibers)
  2. Tousch (medium fibers)
  3. Proprioception (joint position - large fibers)
  4. Motor Control (largest fibers)
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4
Q

How electrical impulses travel along the nerve:

A
  • electrical impulses are generated at the terminal
  • impulses travel up the nerve fiber through the opening of Sodium channels
  • eletrical impulses travel along the nerve by the opening of sodium channels in the nodes of ranvier
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5
Q

larger nerve fibers conduct impulses more quickly b/c:

A
  • have a large intranodal distance

aka they have larger myelinated sections

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6
Q

Local anesthetics block nerve impulse by:

A
  • block conduction

- need to block 2 or more nodes to prevent transmition

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7
Q

Why are functions local anesthetics lost in this order:

A
  • on smaller fibers the nodes of ranvier are closer together making them easier to block
  • the larger the fibers the larger the intranodal distance, therefore it requires more anesthetic to be blocked
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8
Q

Mechanism of Tetrodotoxin and Saxitoxin toxin:

A
  • local anesthetics
  • block sodium channels
  • they block the reuptake of sodium after a cell has depolarized
  • block from the outside
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9
Q

Ester Local Anesthetics Contain:

A
  • ester
  • lipophilic group attached to the ester - usually aromatic ring
  • contain 2 R groups
  • one needs to be hydrophilic (can be primary, secondary, or tertiary)
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10
Q

Amide Local Anesthetics Contain:

A
  • amide
  • lipophilic group attached to the nitrogen
  • contains 1 R group
  • R group needs to be hydrophilic (can be primary, secondary, or tertiary)
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11
Q

Mechanism of Local Anesthetics:

A
  • block sodium channels
  • cross the cell membrane in unionized form
  • then ionize to block the reuptake of sodium into the cell
  • block reuptake from the inside of the cell
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12
Q

How local pH affects onset of local anesthetics:

A
  • affects the ratio of unionized to ionized drug

- which affects the activity(efficacy) of the drug

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13
Q

How blood flow affects duration of local anesthetics:

A
  • faster the blood flow the quicker the drug will be taken away from where it is acting
  • when it is taken away from where it is acting it is no longer effective
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14
Q

How metabolism affects the onset/duration of local anesthetics:

A
  • metabolism has no affect on the onset or duration of action because for metabolism to occur it must get into the blood
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15
Q

How esters are broken down:

A
  • plasma esterases (pseudocholinesterase)
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16
Q

How amides are broken down:

A
  • in the liver by N-dealylation and hydrolysis
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17
Q

Local Anesthetics containing esters:

A
  • Procaine

- Benzocaine

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18
Q

Local Anesthetics containing amides:

A
  • Lidocaine

- Bupivacaine

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19
Q

Administration of Procaine

A

Infiltration (dental)

20
Q

Administration of Benzocaine

A

Topical (skin, mucous membranes)

21
Q

Adminidtration of Lidocaine

A

All routes: topical, infiltration, epidural, caudal, spinal

22
Q

Administration of Bupivacaine

A

All routes: topical, infiltration, epidural, caudal, spinal

23
Q

Approximate pKa’s:

A 
Procaine = 8.7
Benzocaine = 2.5
Lidocaine = 7.9
Bupivacaine = 8.1
24
Q

Procaine Lipid Solubility

A

very low

25
Q

Benzocaine Lipid Solubility

A

Moderate (water insoluble)

26
Q

Lidocaine Lipid Solubility

A

Moderate

27
Q

Bupivacaine Lipid Solubility

A

High

28
Q

Procaine Duration of Action

A

~60 min

29
Q

Benzocaine Duration of Action

A

While in contact

30
Q

Lidocaine Duration of Action

A

90-200 min

31
Q

Bupivacaine Duration of Action

A

180-600min

32
Q

Procaine Toxicity

A

Low

33
Q

Benzocaine Toxicity

A

Methemiglobinemia

34
Q

Lidocaine Toxicity

A

Moderate (can be absorbed and cause systemic toxicity)

35
Q

Bupivacaine Toxicity

A

High (cardiotoxic)

36
Q

Different Route of Administration

A
  1. Topical or Surface
  2. Infiltration
  3. Nerve Block
  4. Spinal
  5. Epidural
37
Q

Topical or Surface Anesthesia

A
  • used on mucous membranes, on a cut or burn (relieves the pain)
38
Q

Infiltration Anestesia

A
  • locally injected

- either directly into the affected tissues or around the area for a ring or field block

39
Q

Nerve Block

A
  • injected around a nerve trunk which inervates the surgical field
  • used for dental procedures or limb surgery
  • blocks motor nerves to produce muscle relaxation
40
Q

Spinal Anesthesia

A
  • Subarachnoid or Intrathecal Injection
  • injected directly into the spinal cord
  • blocks everything from that point down
  • rapid onset - 5-10min
41
Q

Epidural Anesthesia

A
  • injected into the space where the neurons enter the spinal cord (not actually in the spinal cord)
  • more segmental
  • more localized spinal anesthesia
42
Q

Central Nervous System Toxicity

A
  • first sign can be lip tingling
  • initial nervousness, dizziness, blurred vision and tremors (can be transient)
  • then drawsiness, convulsions, unconsciousness, respiratory arrest
  • caused by the direct effect of local anesthesia on euronal sodium chnnels
    (keep patients well hydrated to avoid toxicity)
43
Q

Cardiotoxicity

A
  • hypotension, cardiovascular collapse, bradycardia, cardiac arrest
  • direct effect of local anesthetics on cardiac and arteriolar sodium channels
  • indirect effect due to sympathetic blockade (spinal/epidural) and central nervous system
44
Q

Local Toxicity

A
  • hypersensitivity - dermatitis to breathing difficulties (more common with esters)
  • prolonged anesthesia - may last for several weeks (more common after prilocaine and articaine dental injections)
45
Q

Toxicity is due to:

A
  • toxic levels systemically and not locally

PHAR 341 - Pharmacology (7 decks)

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