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Pharmacology > Local Anaesthetic agents > Flashcards

Local Anaesthetic agents Flashcards

1
Q

Local anaesthesia function?

A

prevents transmission of
the nerve impulse in the
region to which it is
applied, without affecting
consciousness

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2
Q

LA Irr/revsersible?

A

revsersible

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3
Q

Local anaesthetics?

A

Local anaesthetics are drugs which upon topical application or local
administration causes reversible loss of sensory perception,
especially pain in a localized area of the body

 No structural damage to neurons

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4
Q

Local anaesthetics chemical structure?

A

-Weak bases
-Lipophilic ring
-Hydrophilic amine
-Intermediate chain: amide or ester

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5
Q

Local anaesthetic topical drugs?

A

Local TOP Benzo’s

Lignocaine
Tetracaine
Oxybuprocaine
Prilocaine
Benzocaine

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6
Q

Local anaesthetic injectable drugs?

A

My Role Leaves Lover Boys

Mepivacaine
Ropivacaine
Lignocaine
Levobupivacine
Bupivacaine

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7
Q

Local anaesthetic MOA?

A

 block voltage-gated sodium channels & reduce influx of sodium
ions
 preventing depolarization of the membrane blocking conduction
of the action potential

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8
Q

LA bases or acids?

A

All LA agents are weak bases

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9
Q

What are the two forms that LA exist in?

A

Unionised and ionised

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10
Q

The importance of pKa of a LA?

A

The pKa of a weak base defines the pH at which both forms exist
in equal amounts

 As the pH of tissues differs from the pKa of the specific drug,
more of the drug exists either in its charged or uncharged form

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11
Q

Relationship of pKa and ionisation for local anaesthetics

A

Decrease in pKA, increases ionisation

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12
Q

Infected tissue pH variations?

A

 Infected tissue reduced pH
 Fraction of unionised LA is reduced –> effect
reduced/ineffective
 Infected tissue increased blood supply - more LA removed
from local area before it can have an effect on the neuron

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13
Q

What makes LA more potent-explain the chemistry too?

A

-Longer hydrocarbon chain length
more lipophilic

-More lipophilic more potent:
penetrates the cell membrane
more easily to exert effect

-Bupivacaine high potency

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14
Q

What affects LA tissue binding ability?

A

-More protein binding. More protein bound, the tighter is binds and longer the duration of action.

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15
Q

Different types of nerve fibres of LA?

A

Type A:(heavy myelination)
Alpha: Proprioception, Motor
Beta: Touch, pressure
Gamma: Muscle Spindle
Delta: Pain, temperature

Type B:(light myelination)
Preganglionic autonomic

Type C:
Dorsal Root-pain(zero myelination)
Sympathetic-post ganglionic(zero myelination)

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16
Q

Influence of LA blocking based on diameter?

A

Small diameter nerve fibers (e.g. C-fibers) are more readily blocked
than large fibers

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17
Q

Influence of LA blocking based on myelination?

A

Myelinated fibers are more susceptible to blockade than unmyelinated fibers of the same size (mechanism not clear)

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18
Q

What order are fibres blocked in?

A
  1. Sympathetic and pain
  2. Temperature
  3. Light touch and proprioception
  4. Motor
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19
Q

What order does recovery of drugs occur in?

A
  1. Motor
  2. Light touch and proprioception
  3. Temperature
  4. Sympathetic and pain
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20
Q

Benefit of motor being last order of LA blockage?

A

This is exploited to produce analgesia with minimal or no motor block,
by using lower concentrations of LA

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21
Q

Addition of vasoconstrictor on LA?

A

Increases duration of action added to injectables

 Localize the anaesthetic at desired site
 Prolongs duration of action of LA
 Reduce local haemorrhage
 Reduce amnt of LA absorbed into
systemic circ
 Decrease toxicity

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22
Q

What are the drug interactions precautions to use of vascoconstrictors?

A

 Tricyclic antidepressants (e.g.: Amitriptyline)
 potentiates hypertensive effect
 Non selective beta blockers (e.g.: Propranolol)
 increase BP, reflex decr HR, monitor BP
 Cocaine, methamphetamine abusers
 increase risk HT crisis, stroke, MI , postpone 24 hours
 Digoxin
 narrow TI, may ppt cardiac arrythmias
 Undergoing general anaesthesia (e.g.: Halothane)
 increase dysrhythmic effects of

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23
Q

Contraindications of vasoconstrictors?

A

 Severe heart disease
 Uncontrolled hyperthyroidism
 Sulphite allergies
 Asthmatics (corticosteroid-dependant)
 Pheochromocytoma-releases and increase overstimulate CNS

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24
Q

LA P/K?

A

LA administered to areas to be
blocked: skin, s.c tissues, intrathecal, epidural spaces

 Some of the drug will be
absorbed into systemic
circulation
 Intrinsic effects of drugs
 Vascularity of tissue/area
 Additives
Pharmacokinetics
 High vascularity to low:
 IV > tracheal > intercostal > caudal > epidural > brachial > sciatic > s.c

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25
Q

Metabolism P/K?

A

ESTERS
 Metabolism
 Plasma cholinesterase’s to
inactive compounds
Shorter time

AMIDES
 Metabolism
 In Liver hepatic cytochromes
Longer process

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26
Q

Administration of LA formulation for oral and injections?

A

 Water solubility of a LA is greatest in its ionised form
 Injectionable preparations are formulated as HCL salts
 Increasing alkalinity of injection solution increases the speed of acti

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27
Q

Several administrations of LA?

A
  1. Topical
  2. Infiltration
  3. Peripheral nerve block
  4. Central nerve block (epidural and spinal)
  5. Intravenous regional
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28
Q

Topical Anaesthesia?

A

 High concentrations of LA in an oily vehicle slowly penetrate the
skin or mucous membrane

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29
Q

Topical Anaesthesia duration?

A

Provides short term pain relief

30
Q

Topical Anaesthesia drugs?

A

Long TOP’s Benzo

Lignocaine
Tetracaine
Oxybuprocaine
Prilocaine
Benzocaine

31
Q

Examples of topical administration of LA?

A

o Creams
o Gels
o Lozenges
o Sprays
o Eye drops
o Patches

32
Q

Infiltration of LA?

A

 LA is injected intradermally or subcutaneously by the area to be
anaesthetised

33
Q

Infiltration of LA time?

A

 Produces numbness faster than topical anaesthesia

34
Q

Infiltration of LA usuage now?

A

 Used extensively in dentistry – lignocaine is the most widely
used injected anaesthetic

35
Q

Infiltration drugs?

A

Mouth Really Be Laughing

Mepivacaine
Ropivacaine
Bupivacaine
Lignocaine

36
Q

Peripheral Nerve Block Anaesthesia?

A

 Injection of LA solution around a nerve trunk
 Produces fields of anaesthesia distal to site of injection

37
Q

Peripheral Nerve block usuage?

A

 E.g. a brachial plexus block is used to anaesthetise the whole
arm

38
Q

Peripheral Nerve Usuage drugs?

A

Bupivacaine
Lignocaine
Mepivacaine
Ropivacaine

39
Q

Central nerve block anaesthesia ?

A

 LA is injected near the spinal cord
 Produces anaesthesia above and below site of injection
 Epidural anaesthesia used extensively during labo

40
Q

Central nerve block anaesthesia drugs?

A

Bupivacaine
Lignocaine
Ropivacaine

41
Q

Intravenous regional anaesthesia?

A

 LA is injected into a limb after application of tourniquet

42
Q

Intravenous uses?

A

 Used for manipulation of fractures and minor surgical
procedures

43
Q

Intravenous IV drug?

A

lignocaine

44
Q

Local Anaesthetic Systemic Toxicity (LAST)?

A

SAMS

Slurred or difficult speech
Altered Central Nervous System
Muscle Twitching
Seizures

45
Q

LA systemic toxicity CNS?

A

Symptoms:

Tingling of lips
Slurred speech
Reduces level of consciousness
Sezures

46
Q

LA systemic toxicity Prevention?

A

Prevention/Treatment

Oxygen for loss of conciousness

Benzodiazepines thiopentone for seizures

47
Q

LA respiratory toxicity mean?

A

Respiratory Arrest

48
Q

LA respiratory toxicity symptoms ?

A

Reduced myocardial
contractility
Arrythmias
Hypotension
Ventricular fibrillation -
bupivacaine

49
Q

LA prevention for hypotension?

A

Vasopressors
(ephedrine/ phenylephrine)
Inotropes
(adrenaline)

50
Q

Prevention of toxicity?

A

 Use max safe dose
 Aspirate regularly during injection
 Adrenaline if appropriate
 Test doses
 Stabilise needle carefully
 Monitor patients vitals

51
Q

Amides -Bupivacaine P/K?

A

 Long-acting LA {doa usually 3 hours, peripheral blocks: 2-24hrs: dose & site}
 Slow onset of action: 30 mins
 Bupivacaine is a potent LA capable of producing prolonged anaesthesia
 Widely used during labour or postoperatively

52
Q

Amides -Bupivacaine I?

A

 Local infiltration, regional block, spinal & epidural anaesthesia
 Chiefly used for surgical anaesthesia (0.5%)
 Useful in providing several days of Analgesia (admin. via indwelling
catheters & continuous infusions)

53
Q

Amides Metabolism?

A

Liver

54
Q

Amides toxicity?

A

Cardiotoxic

55
Q

Amides-lignocaine indications?

A

INDICATIONS:
 Local/topical
 Infiltration
 Intravenous regional anaesthesia (biers block)
 Epidural anaesthesia
 Eye block

56
Q

Amides-lignocaine P/K?

A

Onset of action: rapid
Duration: Intermediate

57
Q

Amides-lignocaine CI?

A

Heart block and conduction disturbance

58
Q

Amides-lignocaine DI?

A

-Cimetidine/Beta Blockers

59
Q

Mepivacaine I?

A

INDICATIONS:
 Infiltration and nerve blocks
 Metabolism: Liver enzymes

60
Q

Mepivacaine Duration?

A

Intermediate acting

61
Q

Ropivacaine duration?

A

LONG ACTING LA

62
Q

Ropivacaine indications?

A

 Epidural anaesthesia
 Local nerve block
 Infiltration
 Analgesia

63
Q

Ropivacain metabolism and cautions?

A

METABOLISM: Liver enzymes
CAUTIONS: partial or complete
heart block, elderly, liver dysfunction

64
Q

Amides-articane I?

A

Infiltration
 Nerve block

65
Q

Amides-articaine P/K?

A

 An amide but contains ester side chain which is hydrolysed - plasma esterases
 Elimination half life: 20-40min
 High lipid solubility - thiophene ring
 Rapid onset

66
Q

Prilocaine P/K?

A

Topical anaesthesia
Available in combination with lignocainE

67
Q

Prilocaine skin P/K?

A

Mucosa: apply and leave unoccluded for 10-15min

Intact skin: apply a thick layer and cover
with an occlusive dressing for 1-2 hours
(analgesia: for +/-2 hrs after removal of
dressing)

68
Q

Lignocaine P/K?

A

 Topical spray: larynx
 Jelly: urethral anaesthesia &
haemorrhoids
 Patch: (5%, S4) neuropathic
pain relief (PHN)

69
Q

Tetracaine uses?

A

Uses:
 Topical cream: pain relief in
haemorrhoids and minor skin burns

 Eye drops: ophthalmology in
tonometry, foreign body removal,
suture removal

 Oral gel: pain relief of mucous
membranes of mouth, lips, gums

70
Q

Benzocaine uses?

A

Topical gel: dentistry injection
sites: minimize sensation
 Lozenge: Surface anaesthetic -
pain relief of sore throats
 Throat spray
 Throat gargl

71
Q

Oxybuprocaine

A

Uses:
 Eye drops: ophthalmology in
tonometry, foreign body removal,
suture removal
 Has additive bactericidal activity

Pharmacology (44 decks)

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