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Pharmacology > Local Anesthetics > Flashcards

Local Anesthetics Flashcards

1
Q

Adding a vasoconstrictor to a local anesthetic does what to it?

A

Increases its duration of action by 50% by reducing systemic absorption

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2
Q

Describe what each part of a local anestetic molecule does:

  1. Lipophilic part:
  2. Intermediate chain:
  3. Hydrophilic part:
A
  1. Lipophilic part: rapid penetration of biological membranes (aromatic part)
  2. Intermediate chain: determines metabolic pathway and allergenicity
  3. Hydrophilic part: ionizable amine- pH determines % of charged vs uncharged (amine part)
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3
Q

Describe how inflammation or infection affects pH tissue and administration of local anesthetics

A

infection or inflammation lowers tissue pH, resulting in a greater fraction of local anesthetic in cationic form [Drug+], less drug diffuses through membranes to site of action, thus less effective pain relief.
**Clinically, this generally results in larger dose being necessary in areas of inflammation.

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4
Q

Which of the following is true about local anesthetics?
A.  They are weak acids
B.  They are strong bases
C.  They are largely in the charged cationic form at normal body pH
D.  The charged form of the drug readily penetrates the cell membrane because of the presence of a hydrophilic group
E.  The non-ionized form of the drug blocks the Na+ channel

A

C.  They are largely in the charged cationic form at normal body pH

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5
Q

Local anesthetics are __.

Which form can readily penetrate the cell membrane?

A

weak bases

  • [Uncharged base] lipophilic form crosses membranes (aromatic)
  • [Charged cation] hydrophilic form increase solubility and stabiity and form that blocks Na channels
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6
Q

Intermediate Chain (ester or amide linkage). Determines __ and __

A

metabolic fate and allergenic potential.

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7
Q

Describe the metabolic fate, allergenic potential, and toxic potential of esters

A
  • metabolized by plasma and liver esterases (results in shorter duration of action, T1//2 minutes) to allergenic metabolites (PABA, with higher incidence of allergic reactions).
  • Low toxic potential
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8
Q

Describe the metabolic fate, allergenic potential, and toxic potential of amides

A
  • metabolized in liver by amidases (major, T1/2 1-3min) and CYP450 enzymes (minor) with potential for interindividual variations in rate.
  • Presence of liver disease or heart failure (ie. reduced hepatic BF) can increase toxic potential
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9
Q

What are examples of ester LA

A
  1. Tetracaine
  2. Cocaine
  3. Benzocaine
  4. procaine (Novocain)
  5. Chloroprocaine
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10
Q

What are examples of amide LA

A
  1. Lidocaine
  2. Mepivacaine
  3. Bupivacaine
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11
Q 
The pKa of lidocaine is 7.7. In infected tissue, which can be acidic, for example at pH 6.7, the percentage of the drug in the nonionized form will be: 
A.  1%
B.  10% 
C.  50% 
D.  90% 
E.  99%
A

B.  10%

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12
Q

What is the henderson hasselbach equation?

A

pH-pKa= log [Drug]/[Drug+]

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13
Q 
Local anesthetics exert their therapeutic effects by which one of the following nerve fiber types? 
A.  Type Aα 
B.  Type Aβ 
C.  Type Aγ 
D.  Type Aδ 
E.  Type B
F.   Type C
A

D.  Type Aδ

F.   Type C

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14
Q

What type of fibers are affected first

A

Small>large
Myelinated>unmyelinated
Small>Myelinated

*sensory pain and postganglionic sympathetic neurons smallest

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15
Q

___ fibers have the highest firing rate

A

activated sensory pain fibers

  • faster the neuronal firing rate–> greater the blocking effect
    ex. of use-dependent blockade
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16
Q

Describe the sensitivity to block - loss of nerve fxn (1st to last) (great interpatient variation)

A

sympathetic pre- / postganglionic [C fiber] → vasodilation) ≥ pain [C fiber > Aδ] ≥ cold > warmth &raquo_space; touch > pressure > vibration > proprioception > motor

*recovery of fxn generally occurs in reverse order

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17
Q

Local anesthetics exert their therapeutic effects primarily by which one of the following mechanisms?
A.  Stimulation of activity-dependent Na+ channels
B.  Blockade of activity-dependent Na+ channels
C.  Blockade of NMDA-glutamate receptors
D.  Blockade of spinal cord mu-opioid receptors
E.  Opening of K+ channels

A

B.  Blockade of activity-dependent Na+ channels

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18
Q

PK has a greater influence on _____

A
  • offset of effects than onset

- related more to toxic effects than therapeutic effects

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19
Q

Describe the absorption of LA

A
  • poor uptake PO or topical (hepatic 1st pass effect destroys agents given orally)
  • Uptake is excellent following injection - SC, IM, IV, but NOT infiltration

-special formulas improve topical absorption (ie. Lidocain forms)

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20
Q

Systemic absorption can be modified by several factors including:

A
  1. Dosage (Higher= more systemic absorption)
  2. Injection site rate (related to vascularity)
  3. Vasodilatory action (reduced w/ vasoconstriction= prolong local effect)
  4. tissue pH
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21
Q

All of the following factors influence the action of local anesthetics EXCEPT:
A.  Tissue pH
B.  The use of vasoconstrictors
C.  Dose of local anesthetic injected
D.  Blood flow through the tissue in which injection is made
E.  Acetylcholinesterase activity in the region of the injection site

A

E.  Acetylcholinesterase activity in the region of the injection site

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22
Q

Describe the distribution of LA

A
  1. Widely distributed (amides>esters)
  2. cross BBB and placenta
  3. Distribution is faster in healthy pts, thus lower initial blood levels
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23
Q

Determinant of systemic toxicity rather than duration

A

metabolism/excretion

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24
Q

LA action is terminated by __

A

diffusion from site of action

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25
Q

Termination of the systemic actions of local anesthetics:
A.  Involves metabolic breakdown primarily by plasma cholinesterase for lidocaine
B.  Involves plasma protein binding primarily with ester type agents
C.  Involves vascular absorption primarily with amide type agents
D.  Is enhanced in the presence of vasoconstrictors such as epinephrine with amide type agents
E.  Involves metabolic breakdown primarily by plasma cholinesterase for chloroprocaine

A

E.  Involves metabolic breakdown primarily by plasma cholinesterase for chloroprocaine

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26
Q

What are systemic adverse effects of LA

A
  1. LA can affect any excitable membrane
  2. Allergenicity (lower w/ amides/ true allergy is rare)
  3. CNS effects
  4. CV effects
  5. Methemoglobinemia (impaired tissue oxygenation)
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27
Q

RF for toxicity are related to:

A
  1. specific agent used
  2. Concentration in systemic circulation–> depends on
  3. Rate, route, and site (vascularity) of injection
  4. Concentration injected
  5. Presence of liver dz
  6. Presence of absence of vasoconstrictors
28
Q

Which statement about the toxicity of local anesthetics is CORRECT?
A.  Bupivacaine is the safest local anesthetic to use in patients at risk for cardiac arrhythmias
B.  Intravenous injection of local anesthetics may stimulate ectopic cardiac pacemaker activity
C.  Most local anesthetics cause vasoconstriction
D.  Serious cardiac reactions are more likely to occur with lidocaine than with bupivacaine
E.  Cocaine may cause cardiac arrhythmias in overdose

A

E.  Cocaine may cause cardiac arrhythmias in overdose

29
Q 
The most important effect of inadvertent intravenous administration of a large dose of lidocaine is: 
A.  Bronchoconstriction 
B.  Methemoglobinemia 
C.  Renal failure
D.  Seizures 
E.  Tachycardia
A

D.  Seizures

30
Q

Describe the allergenicity SE that occurs w/ esters

A

*Hydrolysis of esters produces PABA –> more allergenic than the parent compounds

  1. Rash,
  2. anaphylactic shock possible
31
Q

Describe the allergenicity SE that occurs w/ amides

A
  • Enzymatic degradation in liver results in low incidence of allergenic compounds
  • True allergies to amides are extremely RARE
32
Q

Describe the systemic CNS SE of LA

A
  • CNS stimulation via depression of cortical inhibitory neurons
    1. LH
    2. Drowsiness [lidocaine]
    3. Restlessness
    4. Shivering
    5. Tremors 3-5 [LD]
    6. Muscle twitching
    7. Nystagmus
    8. Shivering 6-8[HD]
    9. proceed to convulsions
    10. CNS depression–> death by resp. failure
33
Q

What is the tx of choice for local anesthetic induced convulsion?

A

Diazepam (Valium) IV

34
Q

Describe the systemic CV SE of LA

A 
*seen only after [high]
Direct action on myocardium (block Na channels)
1. Decrease excitability
2. decrease conduction rate
3. decrease contraction strength

Used as antiarrhythmic agent

  1. Hypotension occurs due to vasodilation
  2. Cardiac arrest may follow accidental IV administration
35
Q

Methemoglobinemia is associated w/ large doses of __ via metabolite production

A

Prolicaine

*Lidocaine and benzocaine used topically are common precipitants

36
Q

Sx of Methomoglobinemia

A
  1. lethargy
  2. resp. distress
  3. Ashen gray skin
  4. sx appear after 3-4hrs
37
Q

How do you tx Methemoglobinemia

A

IV administration of methylene blue

38
Q

Describe what happens in methemoglobinemia

A

Hemoglobin is oxidized from Fe++ state to Fe+++ state (methemoglobin)–> carrys O2 poorly

39
Q

Describe Uses of LA that provide temporary but complete anaglesia

A
  1. Surface on mucous membranes
  2. Infiltration under the skin (requires large dose)
  3. Regional nerve block (inject near nerve)
  4. Spinal (subarachnoid space)- cord transection
  5. Epidural (lumbar)- in obestetrics
  6. Epidural (caudal)- above coccyx for rectal and perineal procedures
40
Q

Which of the following is correct regarding local anesthetics?
A.  They affect only small, unmyelinated neurons
B.  They have either a lipophilic or a hydrophilic group
C.  They have either an amide or an ester linkage
D.  They are unaffected by pH of the tissue or pKa of the specific agent
E.  In their ionized form they interact with the protein receptor of the voltage-sensitive sodium channel

A

C.  They have either an amide or an ester linkage

E.  In their ionized form they interact with the protein receptor of the voltage-sensitive sodium channel

41
Q

Characteristic properties of local anesthetics include all of the following EXCEPT:
A.  An increase in membrane refractory period
B.  Blockade of voltage-dependent sodium channels
C.  Effects on vascular tissue
D.  Preferential binding to resting channels
E.  Slowing of axonal impulse conduction

A

D.  Preferential binding to resting channels

42
Q

Describe the onset, duration, and relative vasodilatory activity of lidocaine

A

Onset: rapid 2-3 min
Duration: intermediate w/ added epi
Vasodilation: moderate (lesser w/o Epi)

43
Q

SE of Lidocaine

A
  1. Drowsiness (MC)
  2. Unconsciousness (TD)
  3. Seizure (TD)
  4. Resp. arrest (TD)
44
Q

Describe the use of lidocaine [Xylocaine]

A
  1. safest for use in pregnancy (cat. B)
  2. Most commonly used LA (via infiltration)
  3. IV arrhythmias
  4. ointment, viscous, spray, topical use
45
Q

Describe the onset, duration, and relative vasodilatory activity of Mepivacaine (Carbocaine)

A

Onset: Rapid (1.5-2min)
Duration: Intermediate
Vasodilation: VERY LOW (LEAST)

46
Q

Uses of Mepivacaine

A
  1. short procedures w/o vasoconstrictor (in those who should avoid vasoconstrictors)
47
Q

SE of Mepivacaine

A
  1. Neurobehavioral effects in newborns
  2. Category D or C
  3. Toxicity similar to lidocaine

**NOT effective topically

48
Q

Describe the onset, duration, and relative vasodilatory activity of Bupivacine (Marcaine, Sensorcaine)

A

Onset: Slower
Duration: Long*
Vasodilation: Highest!–> requires use of vasoconstrictor

49
Q

Uses of Bupivacine (Marcaine, Sensorcaine)

A
  1. Prolonged procedures where postoperative pain is expected
  2. Endodontic
  3. Periodontal surgery
  4. epidural anesthetic in obstetrics (cat. C)
50
Q

SE of Bupivacine (Marcaine, Sensorcaine)

A
  • less overall general toxicity
    1. long duration may lead to inadvertent post-op chewing or biting troubles
    2. more cardiotoxic when given IV
    3. Block cardiac Na channels–>
    4. slowed conduction
    5. decreased contractility
51
Q 
A 32-year-old woman requests an epidural to ease labor pains. She reports she had an allergic reaction to procaine at the dentist’s office. Which of the following local anesthetics would be appropriate for this patient? 
A.  Chloroprocaine 
B.  Mepivacaine 
C.  Bupivacaine 
D.  Tetracaine 
E.  Lidocaine
A

C.  Bupivacaine**

E.  Lidocaine

52
Q

Very potent, extremely toxic and addictive (via block of DA reuptake in limbic system)

A

Cocaine (ester)

53
Q

SE of Cocaine

A
  1. Death from HF (immediate)
  2. Respiratory failure (eventual)
  3. pyrogenic
54
Q

Least toxic of the ester local anesthetics

A

Chloroprocaine

*bc metabolized very rapidly by plasma cholinesterases (pseudocholinesterase)

55
Q

Describe the onset and duration of Chloroprocaine

A

Onset: fast
Duration: short

56
Q

Describe the onset and duration of Tetracaine

A

Onset: slow
Duration: long

57
Q

Compare the potency and toxicity of tetracaine to procaine

A

10x more potent and toxic– related to very slow rate of metabolism

58
Q

forms of Tetracaine

A

Topically*, spray, solution, ointment

*absorption from mucosal surfaces may produce systemic toxicity

59
Q

Describe the onset and duration of Procaine

A

Onset: slow
Duration: short (limits utility)– longer w/ epi

60
Q

Use of benzocaine

A
  1. Primary use as topical anesthetic - found in numerous teething products
61
Q

SE of Benzocaine

A
  1. Minimal absorption (low solubility) results in low systemic toxicity BUT prone to sensitization reactions
  2. CI in known sensitivity to PABA products
  3. Methomeoglobinemia w/ higher concentration sprays
62
Q

Describe the inherent vasodilating propertiers of LA

A

Bupivacaine (high) > Lidocaine (moderate) >

Mepivacaine (very low)

63
Q

REMEMBER: Pain blocking doses of local anesthetics also block sympathetic vessel tone –> vasodilation
Vasodilation then results in:

A
  1. increase BF to site of injection
  2. reduction in local anesthetic therapeutic effects locally
  3. increase in LA toxic effects systemically
64
Q

What is the rationale for adding vasoconstrictors to LA

A
  1. decrease BF to site of injection resulting in an action to:
  2. prolong and increase depth of LA
  3. reduce toxic effect
  4. Reduce tendency for hemorrhage (HD)
65
Q

Signs and Sx of vasoconstrictor (Epi) toxicity

A
  1. Feat-anxiety
  2. restlessness
  3. dizzy
  4. throbbing
  5. HA
  6. Increase HR
  7. increase BP
  8. tremors
  9. palpitations
  10. arrhythmias
  11. tissue damage (local toxicity) due to increase O2 consumption and hypoxia esp. in extremities
66
Q

Vasoconstrictors (epi) is safe for use in CV patients IF

A

systemic absorption is minimized

  1. lowest dose possible
  2. aspiration technique of injection
  3. very slow injection rate
67
Q 
You have a vial containing 10 ml of a 2% solution of lidocaine. How much lidocaine is present in 1 ml? 
A.  2 mg
B.  5 mg
C.  10 mg 
D.  20 mg
E.  50 mg
A

D.  20 mg

Pharmacology (31 decks)

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