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Dental Pharm Exam 5 > Local Anesthetic > Flashcards

Local Anesthetic Flashcards

1
Q

What do afferent nociceptors and what fibers do they include?

A
  1. Thermal, intense mechanical, chemical stimulation

2. A-delta and C fibers

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2
Q

How do local anesthetics work?

A

Block voltage gated sodium channels on nerve membranes

  1. Inhibit generation of AP
  2. Inhibit conductance of AP
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3
Q

Where do LA’s bind to sodium channels?

A

on the INTRACELLULAR side of the sodium channel

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4
Q

What types of LAs reach their sites of action more readily?

A 
Lipid Soluble (uncharged) Form
Weak Bases
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5
Q

What is a weak base?

A

Neutral compound that can form into a cation by combining w/ a proton
H+ + B –> HB+

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6
Q

pKa range of LAs?

A

7.5 - 9.5

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7
Q

Are LAs more effective at low or high pH

A

High (more basic)

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8
Q

How do lower pKa LAs compare to Higher pKa LAs?

A
  1. Lower - closer to physiological pH, more drug is unprotenated/neutral, more drug penetrates the cellular membrane, FASTER ACTING
  2. Higher - further form physiological pH, less drug unprotonated, less drug penetrating cell membrane, SLOWER ACTING
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9
Q

How does pH at the site of action effect the LA?

A

If pH is lower, the LA will be less effective

1. Inflammation/infection = lower pH, reduced effectiveness of LA

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10
Q

What are the different types of nerve blocks?

A
  1. Fiber diamter/myelination
  2. Firing Frequency
  3. Position of fiber in nerve bundle
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11
Q

How does fiber diameter/myelination effect nerve block?

A
  1. Large nerves are less suceptible to block than smaller nerves
  2. Myelinated nerves are less susceptible than non-myelinated nerves
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12
Q

How does firing frequency effect nerve block?

A

LAs bind active channels more readily than resting channels

LAs have greater effects on more active, frequently firing nerves

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13
Q

How does posiiton of fiber in a nerve bundle effect block?

A

Superficial fibers in a bundle are more accessible to LA than nerve fibers in the “Core” of the nerve bundle

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14
Q

What is the general order of nerve function loss?

A 
Sympathetic
Pain
Cold
Warm
Touch
Motor
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15
Q

What is the critical length hypothesis?

A
  1. For an LA to be effective, the field of action must include at least 3 nodes of an axon
    * the bigger the axon, the longer the myelin segment and the fewer nodes w/in a given field
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16
Q

How are LAs classified

A

Based on linkage between aromatic group and intermediate chain

  1. Amides
  2. Esters
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17
Q

What LAs are Amides? (6)

A
  1. Lidocaine
  2. Mepivicaine
  3. Prilocaine
  4. Bupivicaine
  5. Articaine
  6. Ropivacaine
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18
Q

What LAs are Esters? (5)

A
  1. Cocaine
  2. Procaine
  3. Proparacaine
  4. Tetracaine
  5. Benzocaine
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19
Q

Facts for Esters (3)

A
  1. Rapidly Hydrolyzed by esterases in blood, decreased anesthetic duration
  2. Esters are esters of PABA, metabolized to PABA derrivatives, yields allergens
  3. Tend to have higher pKAs than amides (slower onset)
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20
Q

Facts of Amides (2)

A
  1. Metabolized by CYP450 in liver (increased duration of action)
  2. Less allergenic
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21
Q

Durations of action of amide anesthetics and which drugs they include

A
  1. Short: prilocaine, lidocaine
  2. Intermediate: mepivicaines, articaine
  3. Long: bupivicaine, ropivicaine
22
Q

Routes of Adminitration of LAs

A
  1. Topical
  2. Infiltration/Nerve Block
  3. Epidural (ouside dura)/Spinal (into subarachnoid space around SC)
    * LA properties vary greatly depending on route of admin
23
Q

Topical, and what drugs are most common

A
  1. Application to the mucous membranes of the mouth, nose, trachea, as gel/spray
  2. Benzocaine or Tetracaine
24
Q

Infiltration, and drugs

A
  1. Injection under skin or mucosa

2. Lidocaine, Mepivicaine, Prilocaine, Articaine, Bupivicaine (all amides)

25
Q

Why are vasoconstrictors used w/ local anesthetics?

A
  1. Prolong duration of anesthesia by preventing diffusion from site of action
  2. limit systemic toxicity
  3. Reduce blood loss for surgical procedures
26
Q

What drugs produce vasoconstriction, and what drugs produce the least vasodilation?

A
  1. Cocaine

2. Mepivicaine and Prilocaine

27
Q

What types of vasoconstrictors are used in LAs and what do they target?

A

Agonsists at Alpha-1 Adrenergic Receptors

  1. Epiniphrine Hydrocholoride: Most common, local injection, only targets alpha 1
  2. Levonordefrin Hydrochloride: less common, selective alpha 1
28
Q

Why should alpha 1 agonists be used w/ caution?

A

They are hypertensive agents, used w/ caution in pt w/ cardiovascular disease:
HTN, angina, history of MI
*Always avoid delivery into systemic circulation, only use via infiltration w/ low doses

29
Q

Drug Interactions of alpha-1 adrenergic agonists

A

Sympathomimetic Drugs - MAOi and adrenergic agonists increase effects potentially resulting in HTN crisis
-Antihypertensive drugs that are alpha-1 ANTAGONISTS can block vasoconstriction

30
Q

What is the most commonly used LA?

How is it used in dentsitry?

A

Lidodcaine

2% Lidocaine Hydrochloride w/ 1:100k epi

31
Q

Benefits of lidocaine?

A
  1. Safe for children
  2. Inexpensive
    3* Lower toxicity and increased stability (amides in general)
32
Q

Other than lidocaine, what amides are used in denstirty?

A
  1. Articaine : similar to lidocaine
  2. Mepivicaine: little vasodilation, no need for vasoconstrictor
  3. Prilocaine: does not need vasoconstrictor
  4. Bupivicaine: prolonged duration of action
33
Q

What esters can be used in dentistry?

A

Benzocaine: used topically as numbing agent

34
Q

How are LAs supplied?

A
  1. 8 mL Cartriage for a syringe
    - w/ vasoconstrictor
    - w/ anti-oxidant (prevents breakdown of drugs)
35
Q

How many mg of Lido is there in a 2% carpule?

A

36 mg Lido
2% = 2g/100mL
= 20mg/mL
1.8mL/carpule X 20mg/mL = 36mg

36
Q

How much epi is in a carp if it is 1:100k epi

A

18 micrograms (ug)
1g/100,000 mL
10ug/mL
1.8mg/carp X 10ug/mL = 18ug

37
Q

What type of drug and what drugs are used to treat pain and itching?

A

Topical LAs

  1. EMLA
  2. LMX-4
  3. Tetracain/benzocaine
38
Q

What drug is used in opthamology?

A

Proparacaine - but repeated admin = corneal damage/blindness

39
Q

What are the indications for topical LA?

A
  1. Pain/itching
  2. Opthamalogy
  3. Otolaryngology
  4. Numbing gel prior to infiltration - benzocaine
  5. Others = cough drops, ear drops, hemorrhoids, oral lesions
  6. Lacerations
40
Q

What topicals can be used to manage minor lacerations?

A
  • Use topical w/ epi
    1. TAC (tetracaine, adrenaline/epi, cocaine)
    2. LET (lidocaine, epi, tetracaine)
41
Q

What can be used to treat major lacerations?

A

Pack w/ agents soaked w/ TAC or LET

42
Q

What can be used to treat Digital Injury?

A

Digital Nerve Block - DO NOT ADMIN EPI

43
Q

W/ epidural/spinal block below L1, where will it be effective?

A

All regions below the diaphragm

44
Q

How is an epidural administered?

A
  1. Needle inserted through ligamentum flavum into epidural space
  2. Catheter introduced via needle and inserted into epidural space
  3. LA (Ropivicaine for child birth) is introduced to produce regional nerve block
45
Q

What 2 Drugs can be used for epidurals, and what are the difference between them?

A
  1. Ropivacaine - long acting for child birth

2. Bupivacaine - more cardiotoxic when delievered epidurally, especially towards pregnant women

46
Q

Effected systems for systemic toxicity in LAs

A
  • Extremely rare w/ proper administration
    1. CNS
    2. Cardiovascular
    3. Hemoglobin
47
Q

CNS toxicity w/ LAs

A

Initially: excitation (talkativeness, lightheadedness, tinnitus, tremors)
Severe: seizures, respiratory depression, coma, death

48
Q

Cardiovascular toxicity w/ LAs

A
  1. Decreased conduction, arrhythmias
  2. High conc can block calcium channels (reducing cardiac fxn)
  3. Hypotension from vasodilation
  4. Reduced autonomic activity; blockade of autonomic nerves
49
Q

Hemoglobin toxicity w/ LAs

A

Prilocaine is safer than most other anesthetic drugs w/ administered acutely, it is metabolized in the liver to a compound that converts hemoglobin to methemoglobin = impaired O2 transport

50
Q

Allergic Reactions associated w/ LAs

A
  1. PABA: metabolite of ESTER anesthetics
    - metabolite of some preservatives in drug preperations
  2. Amides are relatively non-allergenic
51
Q

Hypersensitivity Rxns w/ LAs

A
  1. Allergic contact dermatitis w/ repeated injections (delayed onset- 24-48 hrs) = localized rash, hives, up to 30% taking ESTER anesthetics
  2. Rare: acute (30-60min) Type I hypersensitivty (life threatening)
    -symptoms: rash, hives, angioedemia, bronchoconstriction, anaphylactic shock
    TX: Oral diphenhydramine (benadryl/antihistamine)
    Subcutaneous epi (1:1000)

Dental Pharm Exam 5 (3 decks)

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