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RUSVM Pharmacology I > Local Anesthetics > Flashcards

Local Anesthetics Flashcards

1
Q

Local anesthetics - Mechanism of action

A

Blockade of voltage-gated Na+ channels in nerve axons (stops action potentials)

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2
Q

Name the three states of Na+ channels

A

Resting - Open - Inactivated

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3
Q

How do most Local Anesthetics reach the binding site?

A

Most cross neuron cell membrane in UNIONIZED form, get to binding site from the inside

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4
Q

Local Anesthetics - Absorption

A

Normally applied DIRECTLY to site of action

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5
Q

Local Anesthetics - Distribution

A

-Action terminated by redistribution (travel away from area)

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6
Q

Local Anesthetics - Distribution - How can you decrease redistribution, to prolong the effects?

A

Use a Vasoconstrictor (*epinephrine)

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7
Q

Local Anesthetics - Metabolism of Ester-type

A

Rapid breakdown by plasma pseudocholinesterases

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8
Q

Local Anesthetics - Metabolism of Amine-type

A

Metabolized in liver

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9
Q

Local Anesthetics - two types

A

Ester & Amine (type of bond between the aromatic group and tertiary amine group)

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10
Q

Local Anesthetics - General structure/ chemistry

A

Aromatic group joined to tertiary amine group by either an amide or an ester “middle” group

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11
Q

Name the Amine Local Anesthetics

A

Lidocaine - Bupivicaine - Mepivicaine - Ropivicaine - Prilocaine - Dibucaine (Cinchocaine)

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12
Q

What do most Local Anesthetics end with?

A

-caine

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13
Q

Name the ester-type Local Anesthetics

A

Procaine - Benzocaine - Proparacaine - Tetracaine - Cocaine

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14
Q

Local Anesthetics - Elimination

A

Excreted through kidneys –> urine

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15
Q

Name the three types of fibers affected by Local Anesthetics

A

A-delta, C, A-alpha

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16
Q

Describe A-delta fibers

A

Small, myelinated fibers (sympathetic/pain) Fast

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17
Q

Describe C fibers

A

Unmyelinated fibers (pain) Slowest

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18
Q

Describe A-alpha fibers

A

Large, myelinated fibers (motor)

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19
Q

Small, myelinated fibers

A

A- delta

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20
Q

Unmyelinated fibers

A

C fibers

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21
Q

Large, myelinated fibers

A

A-alpha

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22
Q

In what order are fibers affected by local anesthetics (by type)

A

A-gamma > C > A-alpha

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23
Q

Local Anesthetics - Differential block

A

Pain & sympathetic transmission is blocked before motor transmission

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24
Q

Local Anesthetics - Differential block benefit

A

Use low enough concentration for one particular area (think epidural) may block pain without affecting much motor transmission

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25
Q

Local Anesthetics - Frequency-dependent block

A

Rapidly-firing nerves preferentially blocked

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26
Q

Which fibers are preferentially blocked in a frequency-dependent block with local anesthetics? What effects can this have?

A

Nerve fibers carrying pain signals - Antiarrhythmic - Anticonvulsant

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27
Q

Local Anesthetics - Clinical pharmacology - Effect of Dose

A

Dose increaed by increasing volume &/or concentration

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28
Q

What happens when you increase the dose of local anesthetics?

A

Larger dose = more rapid onset of action & longer duration (sometimes)

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29
Q

Local Anesthetics - How can the potency be increased?

A

Potency increases by increasing lipid & water solubility (more potent LA, more myocardium depression)

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30
Q

What does increasing lipophilicity do?

A

Increases penetration into cell –> increases binding with Na+ channels

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31
Q

What does increasing hydrophilicity do?

A

Increases diffusion to the site of action

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32
Q

Local Anesthetics - Onset of action variables

A

Depends on placement of drug, concentration, molecule size, lipophilicity, protein binding, degree of ionization of drug

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33
Q

How does pKa affect Local Anesthetics onset of action?

A

Lower the pKa, more unionized drug to penetrate into the axon

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34
Q

Local Anesthetics - Duration of action variables

A

Depends on drug penetration into axon (lipophilicity), binding to Na+ channel, continuous presence/absence (vasoconstriction to reduce redistribution)

35
Q

Local Anesthetics - Clinical uses

A

Regional anesthesia - Operative anesthesia - Postoperative analgesia - Diagnosing lameness (not with epi) - Ventricular arrhythmias (not with epi!)

36
Q

Local Anesthetics - use as an operative anestesia

A

Usually needs additional sedation, except in ruminants

37
Q

What are minor uses for Local Anesthetics

A

small effect on convulsions & to reduce intracranial pressure

38
Q

Local Anesthetics - Routes of administration

A

Topical - Local infiltration - Peripheral nerve block - Intra-articular - Epidural - Intrathecal - Intravenous regional anesthesia (IVRA) Bier’s Block w/tourniquet

39
Q

Local Anesthetics - Adverse effects

A

CNS stimulation - CNS depression - CV depression - Local irritation - Methemoglobinemia - Histamine release -

40
Q

Local Anesthetics - Adverse effects - CNS stimulation. Which drugs?

A

Muscle twitching, tremors, convulsions, seizures (Diazepam, midazolam)

41
Q

Local Anesthetics - Adverse effects - CNS depression

A

Unconsciousness & respiratory arrest (give artificial respiration)

42
Q

Local Anesthetics - Adverse effects - CV depression

A

Bradycardia - Dysarrythmias - Decreased cardiac contractility - Vasodilation - Hypotension (more potent LA, more myocardium depression)

43
Q

See graph of LA adverse effects

A

Triangle graph

44
Q

Local Anesthetics - Adverse effects - Local irritation

A

Of skeletal muscles & nerves @injection site

45
Q

Local Anesthetics - Adverse effects - Methemoglobinemia

A

From toxic metabolites (benzocaine, O-toluidine for prilocaine)

46
Q

Local Anesthetics - Adverse effects - Histamine release

A

Ester LA & Methylparaben (lidocaine preservative) cause this due to metabolite bi-product PABA

47
Q

What does PABA do?

A

Inhibits antibacterial effect of sulfonamides

48
Q

Procaine

A

Ester LA - Slow onset/ short duration - Poor penetration - Rapid metabolism to PABA - Toxic - DO NOT USE -

49
Q

What toxic effect does procaine have on horses?

A

CNS stimulation!

50
Q

Why should caution be used with penicillin G?

A

Some preparations contain procaine (slows antibiotic’s absorption from muscle)

51
Q

Lidocaine

A

Amide LA - MOST commonly used LA in vet med - 5min onset - 40-60min duration (with epi)

52
Q

What is the most commonly used local anesthetic in vet med?

A

Lidocaine!

53
Q

What are the appropriate doses / preparations for lidocaine?

A

1-2% parentally - 4% topically (gel/ointment/solution/sprays/patches)

54
Q

Lidocaine clinical uses

A

Ventricular arrhythmias - supplement general anesthesia - endotracheal intubation in cats - MINOR anticonvulsant & decreaser of intracranial pressure)

55
Q

What type of antiarrhythmic drug is lidocaine?

A

IB antiarrhythmic

56
Q

What is the maximum does of Lidocaine? What species is most sensitive?

A

Max does = 7mk/kg - Sheep most sensitive

57
Q

What can lidocaine be used in combination with?

A

Oxytetracycline

58
Q

What can lidocaine be combined with for euthanasia?

A

Embutramide

59
Q

Mepivacaine

A

Amide LA - Like lidocaine but less irritant - Diagnostic nerve block in horses

60
Q

Bupivacaine

A

Amide LA - Widely used (not topical - 20min onset - 8h duration (long!) - the MOST cardiotoxic LA

61
Q

What is the most cardiotoxic local anesthetic?

A

Bupivicaine

62
Q

What is the maximum dose of Bupivicaine?

63
Q

What are the enantiomers of bupivicaine?

A

S(-) and R(+) = enantiomers S(-) =levobupivicaine

64
Q

Ropivacaine

A

Amide LA - Similar to bupivacaine - Shorter duration - less toxic

65
Q

Ropivacaine enantiomer

A

S(-) = enantiomer of propivacaine

66
Q

Which drug is used as a diagnostic nerve block in horses?

A

Mepivacaine

67
Q

Prilocaine

A

Amide LA - similar, less toxic than lidocaine - IV regional anesthesia - Methemoglobinemia risk

68
Q

How does methemoglobinemia happen from prilocaine use?

A

Metabolic by-product O-toluidine

69
Q

Benzocaine

A

Ester LA - Lowest pKa (2.5) - Unionized - Low solubility - Topical absorption only

70
Q

What is Benzocaine metabolized to?

A

PABA (think histamine release)

71
Q

Negative side effects of benzocaine

A

PABA –> Histamine release - Methemoglobinemia

72
Q

What use does benzocaine have in aquatic medicine?

A

General anesthesia of fishes

73
Q

EMLA cream

A

(2.5%) Lidocaine/ (2.5%) Prilocaine - 20-30min onset - Dermal analgesia (5mm depth) - Facilitates percutaneous vascular catheterization

74
Q

Proparacaine

A

Ester LA - Topical - 30sec onset - 10-20min duration - Less irritating than tetracaine

75
Q

What is topical proparacaine used for?

A

Corneal & conjunctival manipulation

76
Q

Tetracaine

A

Ester LA - Topical - Intrathecal - Euthanasia

77
Q

What is topical tetracaine used for?

A

Corneal & conjunctival manipulation (last longer than proparacaine)

78
Q

What two local anesthetics are used for corneal & conjunctival manipulation?

A

Tetracaine & Proparacaine

79
Q

What is tetracaine combined with for euthanasia?

A

Embutramide + Tetracaine = death

80
Q

Cocaine

A

Topical anesthesia of nasal - highly addictive (schedule II) - No reason to use in vet med

81
Q

Dibucaine

A

AKA Cinchocaine - Most potent & toxic LA - Combine with secobarbital for euthanasia

82
Q

Politics (which drug is banned where and why?)

A

Lidocaine banned in food animals in europe (even though people still use lidocaine) - Metabolite 2,6 xylidine may be carcinogenic

83
Q

Know tissue and type of sodium channels chart:

RUSVM Pharmacology I (19 decks)

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