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Pharmacology II > Lecture 27: Local Anesthetics and Euthanasia > Flashcards

Lecture 27: Local Anesthetics and Euthanasia Flashcards

1
Q

Local anesthetics are either __ or __

A

Esters or amides

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2
Q

Which have shorter duration of action: esters or amides

A

Esters

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3
Q

Which have increased systemic toxicity: esters or amides

A

Esters

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4
Q

Esters and amides are typically administered as ___to increase stability and solubility

A

Salts

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5
Q

Local anesthetics are weak ___with pKa’s ___

A

Bases, 7.5-9

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6
Q

At physiological pH local anesthetics are predominately ionized or non-ionized?

A

Ionized

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7
Q

Where is the binding site for local anesthetics

A

Inner membrane

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8
Q

Local anesthetics need to be ___to cross the cell membrane

A

Non-ionized

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9
Q

Once inside the cell, local anesthetics become ___

A

Ionized

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10
Q

The ionized form of local anesthetics binds to ___channels

A

Na+

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11
Q

What is the hydrophobic pathway

A

Neutral local anesthetics through the membrane

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12
Q

If you have an abscess where do you want to apply local anesthetic and why

A

0.5-1 inches away from abscess because abscesses are acidic so it will become ionized and not penetrate abscesses and therefore animal will feel everything

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13
Q

What is the mechanism of action for local anesthetics

A

Blocks Na+ channels and inhibits neuronal firing

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14
Q

Local anesthetic have high affinity for what Na+ channels and low affinity for what Na+ channels

A

High affinity: activated/ open and inactivated channels

Low affinity: resting/ closed channels

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15
Q

Local anesthetic blocks are ore effective in ___firing axons than ___axons

A

Rapidly firing, resting axons

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16
Q

Extent of a local anesthetic block is ___ and ___ dependent

A

Voltage (potential) and time (firing)

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17
Q

Local anesthetics increase the threshold for excitation due to ___

A

Decreasing Na+ influx

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18
Q

Local anesthetic slows impulse conduction as more ___are blocked

A

Channels

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19
Q

Complete block from local anesthetic results from progressive ___

A

Decrease in the rate of action potential firing

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20
Q

Duration of action for local anesthetics is dependent on ___

A

Time at site of action

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21
Q

T or F: local anesthetics rapidly diffuse away from site of application

A

True

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22
Q

What affects systemic absoprtion

A
  1. Dosage
  2. Site of injection (vascular vs fat)
  3. Drug tissue binding
  4. Chemical properties of drugs
  5. Local blood flow
  6. Vasoconstricting agents- epinephrine
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23
Q

How does epinephrine affect systemic absoprtion

A
  1. Decreases diffusion of drug
  2. Prolongs duration of action
  3. Decreases systemic absoprtion
  4. Decreases systemic toxicity

Vasoconstricts

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24
Q

Why would you need to space out blebs of local anesthetic when performing a line block with epinephrine in a cow

A

Because epinephrine will vasoconstrict and you can get tissue necrosis

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25
Q

How are amides metabolized

A

Liver by CYP450s

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26
Q

Toxicity from amides is more likely in what patients

A

Patients with hepatic disease of reduced hepatic blood flow

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27
Q

How are esters metabolized

A

Butyrylcholinesterases in the plasma

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28
Q

How are esters and amides eliminated

A

Renal

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29
Q

What are some local adverse effects of esters and amides

A
  1. Tissue damage from injection rare, but increased with epinephrine 2. Neurotoxicity and myotoxicity
30
Q

Bupivicaine is __toxic at __concentrations that lidocaine

A

More, lower plasma concentrations

31
Q

What are the CNS adverse effects from esters and amides

A

Skeletal muscle twitches (1st sign) and then followed by tonic-colonic seizures

32
Q

What is first sign of toxicity from esters and amides

A

Skeletal muscle twitches

33
Q

What adverse effect is associated with the use of benzocaine in cats and rabbits

A

Methemoglobinemia

34
Q

What are some cardiovascular adverse effects from local anesthetics

A
  1. Prolonged PR and QRS intervals
  2. Hypotension and decreased myocardial strength (negative ionotropic effect)
35
Q

Plasma concentrations of lidocaine that produce cardiovascular toxicity may be lower for __than other species

A

Cats

36
Q

All local anesthetics used peri-operatively have ___effects

A

MAC lowering

37
Q

What are some local applications for lidocaine

A
  1. Infiltration, nerve block, epidural in most species
  2. Moderate topical activity and minimal local irritation
38
Q

Intermediate duration of action of lidocaine is dependent on addition of ___

A

Epinephrine (increase duration of action because vasoconstriction)

39
Q

What are some systemic uses for lidocaine

A
  1. Ventricular fibrillation and tachycardia in dogs
  2. Pro kinetic effects in horses with post-sx ileus
40
Q

What are some toxicities associated with lidocaine

A

Profound cardio-depression and greater CNS effects in cats

41
Q

What are some indications for bupivicaine

A
  1. Spinal anesthesia, infiltration blocks, and epidural anesthesia
  2. Anesthesia for post-op pain control
42
Q

What is bupivicaine-liposome labeled for

A

Cranial crucitate ligament sx

43
Q

Which has a longer duration of action: bupivicaine or lidocaine

A

Bupivicaine

44
Q

Why does bupivicaine have longer duration of action than lidocaine

A
  1. Binds more resting cardiac Na+ channels
  2. Dissociates from channel slower (increase risk of cardiac adverse effects)
45
Q

Bupivicaine is a more potent ___block than __block

A

Sensory, motor

46
Q

Which amide has greater cardiotoxicity and why

A

Bupivicaine because binds more resting cardiac Na+ channels and slower dissociation from channel

47
Q

What is mepivicaine used for in horses

A
  1. Epidural and ventriculectomy sx (recurrent laryngeal neuropathy)
  2. Limb blocks
48
Q

Mepivicaine is useful for limb blocks because it does not cause post injection ___

A

Edema

49
Q

T or F: you combine mepivicaine with epinephrine

A

False

50
Q

T or F: mepivicaine is slightly more potent and toxic than lidocaine

A

True

51
Q

What is ropivicaine used for

A
  1. Epidural, infiltration blocks, and local blocks
52
Q

T or F: ropivicaine has a slower onset and longer duration than lidocaine

A

True

53
Q

What is benzocaine used for

A

Historically for fish anesthesia/euthanasia

54
Q

What is proparacaine used for

A

Topical use in ophthalmologic diagnostic procedures (tonometry)

55
Q

What is tetracaine used for

A

Ophthalmological procedures needing a deeper plane or longer duration of anesthesia than can be provided by proparacaine

56
Q

What is the duration of action for tetracaine in dogs

A

30 minutes

57
Q

What are some adverse effects of tetracaine

A
  1. Burning sensation, itching, chemosis
  2. Diffuse epithelial keratitis
  3. Iritis, descemetitis and diffuse stromal edema
  4. Suppresses blink reflex- risk of corneal pacification and keratitis
58
Q

Tetracaine suppresses blink reflex and therefore you need ___ and ___ protection

A

Surgical gel and eye protection

59
Q

What order must euthanasia loss of physiological function occur in

A
  1. Loss of consciousness
  2. Loss of motor function
  3. Arrest of respiratory and cardiac functions
  4. Permanent loss of brain function
60
Q

Loss of motor, respiratory or cardiac function can precede loss of conscious if ___agents are used

A

Paralytic agents

61
Q

Rabbits and chickens have __which must not be confused with loss of consciousness

A

Fear-induced tonic immobility

62
Q

Revisions to AVMA euthanasia guidelines are required every __years

A

10 years

63
Q

What is the preferred agent of euthanasia for non- food producing animals

A

Barbiturates

64
Q

What factors should be considered when selecting best procedure for euthanasia

A
  1. Reliability to induce loss of consciousness, minimize pain and distress
  2. Time
  3. Compatibility of drug with animal
  4. Emotional effect for observers
  5. Drug availability and human abuse potential
  6. Legal requirements
65
Q

Barbiturates must be administered __to be acceptable for euthanasia

A

IV

66
Q

What is mechanism of action of barbiturates

A
  1. Depress CNS starting with cerebral cortex and loss of consciousness progressing to anesthesia
  2. Deep anesthesia progresses to apnea, followed by cardiac arrest
67
Q

What does Beuthanasia D special combine for euthanasia

A

Pentobarbital and phenytoin

68
Q

Barbiturates are never to be used in what animals

A

Animals enter food chain/ food producing animals

69
Q

What is correct disposal of animals euthanized with barbiturates

A
  1. Cremation
  2. Burial can be considered but risk be scavenged
70
Q

What agents can be used to combine with barbiturates to help induce rapid loss of consciousness, muscle relaxation, minimize distress, facilitate restrict, and better environment for owners

A

Ketamine, detomidine

Pharmacology II (36 decks)

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