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RUSVM Pharmacology I > Local Anesthetics > Flashcards

Local Anesthetics Flashcards

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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
Local Anesthetics - Frequency-dependent block
Rapidly-firing nerves preferentially blocked
26
Which fibers are preferentially blocked in a frequency-dependent block with local anesthetics? What effects can this have?
Nerve fibers carrying pain signals - Antiarrhythmic - Anticonvulsant
27
Local Anesthetics - Clinical pharmacology - Effect of Dose
Dose increaed by increasing volume &/or concentration
28
What happens when you increase the dose of local anesthetics?
Larger dose = more rapid onset of action & longer duration (sometimes)
29
Local Anesthetics - How can the potency be increased?
Potency increases by increasing lipid & water solubility (more potent LA, more myocardium depression)
30
What does increasing lipophilicity do?
Increases penetration into cell --\> increases binding with Na+ channels
31
What does increasing hydrophilicity do?
Increases diffusion to the site of action
32
Local Anesthetics - Onset of action variables
Depends on placement of drug, concentration, molecule size, lipophilicity, protein binding, degree of ionization of drug
33
How does pKa affect Local Anesthetics onset of action?
Lower the pKa, more unionized drug to penetrate into the axon
34
Local Anesthetics - Duration of action variables
Depends on drug penetration into axon (lipophilicity), binding to Na+ channel, continuous presence/absence (vasoconstriction to reduce redistribution)
35
Local Anesthetics - Clinical uses
Regional anesthesia - Operative anesthesia - Postoperative analgesia - Diagnosing lameness (not with epi) - Ventricular arrhythmias (not with epi!)
36
Local Anesthetics - use as an operative anestesia
Usually needs additional sedation, except in ruminants
37
What are minor uses for Local Anesthetics
small effect on convulsions & to reduce intracranial pressure
38
Local Anesthetics - Routes of administration
Topical - Local infiltration - Peripheral nerve block - Intra-articular - Epidural - Intrathecal - Intravenous regional anesthesia (IVRA) Bier's Block w/tourniquet
39
Local Anesthetics - Adverse effects
CNS stimulation - CNS depression - CV depression - Local irritation - Methemoglobinemia - Histamine release -
40
Local Anesthetics - Adverse effects - CNS stimulation. Which drugs?
Muscle twitching, tremors, convulsions, seizures (Diazepam, midazolam)
41
Local Anesthetics - Adverse effects - CNS depression
Unconsciousness & respiratory arrest (give artificial respiration)
42
Local Anesthetics - Adverse effects - CV depression
Bradycardia - Dysarrythmias - Decreased cardiac contractility - Vasodilation - Hypotension (more potent LA, more myocardium depression)
43
See graph of LA adverse effects
Triangle graph
44
Local Anesthetics - Adverse effects - Local irritation
Of skeletal muscles & nerves @injection site
45
Local Anesthetics - Adverse effects - Methemoglobinemia
From toxic metabolites (benzocaine, O-toluidine for prilocaine)
46
Local Anesthetics - Adverse effects - Histamine release
Ester LA & Methylparaben (lidocaine preservative) cause this due to metabolite bi-product PABA
47
What does PABA do?
Inhibits antibacterial effect of sulfonamides
48
Procaine
Ester LA - Slow onset/ short duration - Poor penetration - Rapid metabolism to PABA - Toxic - DO NOT USE -
49
What toxic effect does procaine have on horses?
CNS stimulation!
50
Why should caution be used with penicillin G?
Some preparations contain procaine (slows antibiotic's absorption from muscle)
51
Lidocaine
Amide LA - MOST commonly used LA in vet med - 5min onset - 40-60min duration (with epi)
52
What is the most commonly used local anesthetic in vet med?
Lidocaine!
53
What are the appropriate doses / preparations for lidocaine?
1-2% parentally - 4% topically (gel/ointment/solution/sprays/patches)
54
Lidocaine clinical uses
Ventricular arrhythmias - supplement general anesthesia - endotracheal intubation in cats - MINOR anticonvulsant & decreaser of intracranial pressure)
55
What type of antiarrhythmic drug is lidocaine?
IB antiarrhythmic
56
What is the maximum does of Lidocaine? What species is most sensitive?
Max does = 7mk/kg - Sheep most sensitive
57
What can lidocaine be used in combination with?
Oxytetracycline
58
What can lidocaine be combined with for euthanasia?
Embutramide
59
Mepivacaine
Amide LA - Like lidocaine but less irritant - Diagnostic nerve block in horses
60
Bupivacaine
Amide LA - Widely used (not topical - 20min onset - 8h duration (long!) - the MOST cardiotoxic LA
61
What is the most cardiotoxic local anesthetic?
Bupivicaine
62
What is the maximum dose of Bupivicaine?
2 mg/kg
63
What are the enantiomers of bupivicaine?
S(-) and R(+) = enantiomers S(-) =levobupivicaine
64
Ropivacaine
Amide LA - Similar to bupivacaine - Shorter duration - less toxic
65
Ropivacaine enantiomer
S(-) = enantiomer of propivacaine
66
Which drug is used as a diagnostic nerve block in horses?
Mepivacaine
67
Prilocaine
Amide LA - similar, less toxic than lidocaine - IV regional anesthesia - Methemoglobinemia risk
68
How does methemoglobinemia happen from prilocaine use?
Metabolic by-product O-toluidine
69
Benzocaine
Ester LA - Lowest pKa (2.5) - Unionized - Low solubility - Topical absorption only
70
What is Benzocaine metabolized to?
PABA (think histamine release)
71
Negative side effects of benzocaine
PABA --\> Histamine release - Methemoglobinemia
72
What use does benzocaine have in aquatic medicine?
General anesthesia of fishes
73
EMLA cream
(2.5%) Lidocaine/ (2.5%) Prilocaine - 20-30min onset - Dermal analgesia (5mm depth) - Facilitates percutaneous vascular catheterization
74
Proparacaine
Ester LA - Topical - 30sec onset - 10-20min duration - Less irritating than tetracaine
75
What is topical proparacaine used for?
Corneal & conjunctival manipulation
76
Tetracaine
Ester LA - Topical - Intrathecal - Euthanasia
77
What is topical tetracaine used for?
Corneal & conjunctival manipulation (last longer than proparacaine)
78
What two local anesthetics are used for corneal & conjunctival manipulation?
Tetracaine & Proparacaine
79
What is tetracaine combined with for euthanasia?
Embutramide + Tetracaine = death
80
Cocaine
Topical anesthesia of nasal - highly addictive (schedule II) - No reason to use in vet med
81
Dibucaine
AKA Cinchocaine - Most potent & toxic LA - Combine with secobarbital for euthanasia
82
Politics (which drug is banned where and why?)
Lidocaine banned in food animals in europe (even though people still use lidocaine) - Metabolite 2,6 xylidine may be carcinogenic
83
Know tissue and type of sodium channels chart:
Chart

RUSVM Pharmacology I (19 decks)

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