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Pharma midterm 1 > Lecture 15 - Local anaesthetics > Flashcards

Lecture 15 - Local anaesthetics Flashcards

1
Q

How does local anaesthetics act?

A

by blocking conduction in nerve fibres

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2
Q

how is the anaesthesia achieved by local anaesthetics?

A

without loss of consciousness or depressed activity of CNS

  • loss of sensation
  • muscle paralysis - depending on type of fibre involved, route of application
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3
Q

What is the normal use of local anaesthetics?

A

block conduction in pain fibres

  • for diagnostic purposes

permit minor surgery

antiarrhythmic treatment

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4
Q

What are the two chemical types of local anaesthetics?

A

esters and amides

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5
Q

give some examples of esters (local anaesthetics)

A

procaine

chloroprocaine

oxybuprocain

tetracaine

benzocaine

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6
Q

give some examples of amides (local anaesthetics=

A

lidocaine

prilocaine

mepivacaine

bupivacaine

ropivacaine

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7
Q

What is the mechanism of action concerning LAs

A

blocks action potential generation by blocking Na+ channels

LAs act in their cationic form (they have to be weak bases), but must reach their site of action by penetrating the nerve sheath and axonal membrane as unionised species

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8
Q

What is the affinity to the LA and the effect of the channel when it is in refractory status?

A

Affinity: small

Effect: inhibition of the opening of sodium ion channels

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9
Q

What is the affinity to an ion channel and the effect of it when it is in closed status?

A

Affinity is large

the effect is: inhibition of reaopening - major effect

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10
Q

What is the affinity and the effect of the ion channel when it is in open status?

A

affinity is large

effect is closing of Na ion channels - minor effect

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11
Q

what is the affinity and the effect of the ion channel when it is in inactivated status?

A

large affinity

the effect is a prolonged refractory period - major effect

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12
Q

In what order is LAs blocking the conduction (axons)?

A

non-myelinated axons

small myelinated

large mylinated

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13
Q

What type trnasmittion is blocked first with LAs?

A

noiciceptice and sympathetic transmission

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14
Q

When the nervous function dissapears, in what order is the different function lost?

A
  1. pain
  2. warmth
  3. touch
  4. deep pressure
  5. motorfunction
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15
Q

In what order is nervous function returning?

A
  1. motor function
  2. deep pressure
  3. touch
  4. wramt
  5. pain
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16
Q

Describe the nerve fibre: Aa, Ab

  1. myelin
  2. diameter
  3. speed of conduction
  4. function
  5. sesnitivity to lidocaine
A
  1. yes
  2. 6-22
  3. 10-85
  4. motoric and proprioceptive
  5. +,++
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17
Q

Describe the nerve fibre: A-gamma

  1. myelin
  2. diameter
  3. speed of conduction
  4. function
  5. sesnitivity to lidocaine
A
  1. yes
  2. 3-6
  3. 15-35
  4. muscle tone
  5. ++
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18
Q

Describe the nerve fibre: Aδ

  1. myelin
  2. diameter
  3. speed of conduction
  4. function
  5. sesnitivity to lidocaine
A
  1. yes
  2. 1-4
  3. 5-25
  4. rapid pain and temperature
  5. +++
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19
Q

Describe the nerve fibre: B

  1. myelin
  2. diameter
  3. speed of conduction
  4. function
  5. sesnitivity to lidocaine
A
  1. yes
  2. <3
  3. 3-15
  4. vasmotor, visceromotor, sudomotor, pilomotor
  5. ++++
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20
Q

Describe the nerve fibre: C (sympathetic)

  1. myelin
  2. diameter
  3. speed of conduction
  4. function
  5. sensitivity to lidocaine
A
  1. no
  2. 0,3-1,3
  3. 0,7-1,3
  4. vasomotor, visceromotor, sudomotor, pilomotor
  5. ++++
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21
Q

Describe the nerve fibre: C dorsal horn

  1. myelin
  2. diameter
  3. speed of conduction
  4. function
  5. sensitivity to lidocaine
A
  1. no
  2. 0,4-1,2
  3. 0,1-2,0
  4. slow pain and temperature
  5. ++++
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22
Q

What are kinetics?

A

study of reaction rate and how they are affected

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23
Q

What are the kinetics of absorption?

A

site of application

dose

if its a vasoconstrictive drug

features of LAs

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24
Q

How long will the effect of a LA last?

A

until the concentration falls below the critical level due totheir absorption from the site of application

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25
Q

How are ester-type LAs metabolised?

A

they are hydrolysed primarly by plasma esterase and degraded by hepatic metabolism

decomposition in tissue and blood circualtion

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26
Q

How is the metabolism of amide LAs?

A

degraded by hepatic inactivation (liver degradation)

27
Q

Which chemical type of LAs are the safest?

A

esters

28
Q

How are the metabolites of LAs excreted?

A

through the kidneys

29
Q

what is the order of clearnace of amides?

A

prilocaine>lidocaine>mepi-/ropicacaine>bupivacaine

30
Q

Esters: procaine

  1. relative potency
  2. onset of action
  3. duration of action
  4. non-ionised (%)
  5. protein binding (%)
  6. lipid solubility (%)
A
  1. 1
  2. slow
  3. 45-60
  4. 3
  5. 6
  6. 0,6
31
Q

Amides: lidocaine

  1. relative potency
  2. onset of action
  3. duration of action
  4. non-ionised (%)
  5. protein binding (%)
  6. lipid solubility (%)
A
  1. 2
  2. rapid
  3. 60-120
  4. 25
  5. 70
  6. 2,9
32
Q

Esters: tetracaine

  1. relative potency
  2. onset of action
  3. duration of action
  4. non-ionised (%)
  5. protein binding (%)
  6. lipid solubility (%)
A
  1. 8
  2. slow
  3. 60-180
  4. 7
  5. 76
  6. 80
33
Q

Amides: mepivacaine

  1. relative potency
  2. onset of action
  3. duration of action
  4. non-ionised (%)
  5. protein binding (%)
  6. lipid solubility (%)
A
  1. 1-5
  2. meidum
  3. 90-180
  4. 39
  5. 77
  6. 1
34
Q

Amides: bupivacaine

  1. relative potency
  2. onset of action
  3. duration of action
  4. non-ionised (%)
  5. protein binding (%)
  6. lipid solubility (%)
A
  1. 8
  2. medium
  3. 180-480
  4. 15
  5. 95
  6. 28
35
Q

What the effect of the protein % of LAs?

A

its the limiting factor

  • cannot get through BBB
36
Q

How are the side effects of LAs?

A

relatively free from hramful side effects

37
Q

Rate the LAs toxicity in increased order

A
  1. mepivacaine
  2. procaine
  3. lidocaine
  4. tetracaine, bupivacaine
38
Q

What are the most common side effects of LAs?

A
  • allergy
  • asthmatic seizure
  • local tissue irritation
  • systemic effects - elevated plasma conc
    • CNS effecs
      • first mild sensory inhibitiom
      • agitation
      • confusion
      • tremors progressing to convulsions
      • respiratory depression
    • cardivascular effects
      • myocardial depression
      • vasodilation
      • fall in blood pressure
  • effect of adjuvant - adrenaline
39
Q

When can absorption of LA cause toxic effects?

A

when the rate of absorption is faster than the rate of elimination

40
Q

how can the rate of absorption of LAs be reduced?

A

with vasoconstrictors

41
Q

What are the uses of LAs??

A

topical anasthesia

local infiltration

perineural injection

intra-articular use

intravenous regional anaesthesia (IVRA)

epidural and spinal (subarachnoid) block

42
Q

Where can LAs be used topically?

A

applied to

the cornea

mucous membranes

skin

43
Q

What is the intension of adding drugs to teh cornea, mucous membranes or skin?

A

cause loss of sensation by paralyzing sensory nerve ending

44
Q

when lidocain or prilocain is added to the skin, how long time does it usually take for the anasthesia to work?

A

60min

45
Q

What form is LAs in when it is applied topically?

A

cream or gels

46
Q

what indications are topically LAs used for?

A

ulcers

opthalmology

oral

rectal

pharyngeal painful diseases before examination

burnings

sun irritation

inflammation of outer, middle ear

intact skin surface

47
Q

What is the common method of adminitrating LA?

A

Local infiltration

48
Q

how do we administer the LAs with local infiltration?

A

numerous SC inj. of small volumes

49
Q

what isthe indications of local infiltration?

A

minor surgery

dentistry (may be ineffective)

castration of males (with sedative, anaesthetics)

subcutaneous regional anaesthesia

50
Q

what happens whn LAs are injected along a line?

A

it will block the conduction in the nerves that passes through the tissue

all regions supplied by the distal section of these nerves will be anaesthetised

51
Q

How is LAs perineural injection performed?

A

its a peripheral nerve block

the anaesthetics is injected in the immediate vicinity of peripheral nerves

52
Q

What are the indications of perneural injections?

A

dentistry

minor surgery - head, legs, hoofs

53
Q

what other blocks than peripheral nerve blocks cna be performed with LAs?

A

paravertebral blocks

intercostal blocks

brachial plexus blocks

54
Q

How are LAs used intra-articular?

A

rarely

its used for diagnostic reasons or for therapeutic indication - operating the affected joint

55
Q

How is LAs administered as an intravenous regional anaesthesia?

A

it should be injected IV dital to a torniquet

only less tocic agents should be administeres - prilocain

used in cattle digit operations

56
Q

How is LAs administered when its used as an spinal block?

A

subarachnoid

lowe dose

single application

57
Q

what is the disadvantage with administering LAs into the spine?

A

spinal cord injury can occur

58
Q

What are the advantages of using LAs in the epidural space or the subarachnoid space?

A

large areas of the body can be anaesthetised with small amount of drugs

59
Q

what are the indications of epidural/spinal administration of LAs

A

surgery of perneal region

anal

peri-anal region

obsteric operations

urology

60
Q

Whare is the place of injection of epidural anasthesia in horses and cattle?

A

first or second intercoccigeal spaces ( caudal anaesthesia=

61
Q

what happens if the epidural is administered higher than indicated?

A

limb paralysis

62
Q

where is the place of injection of epidural anaestheisa in dog, sheep and pig?

A

at the lumbosacral space

lumbral anaesthesia

63
Q

how much lidocain 1% is administered in

  • large animals
  • dogs, pigs
A
  • 60-80ml
  • according to body size
    • 40cm= 2ml
    • 60cm=5ml
    • 80cm=8ml
    • 100cm=10,75ml
64
Q

Posology of certain local anaesthetic

doses in % of solution

procain

tetracaine

lidocaine

bupivac

mepivac

A

Pharma midterm 1 (14 decks)

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