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3 Pain and pain management > LA Pharmacology 1 > Flashcards

LA Pharmacology 1 Flashcards

1
Q

explain the structure of LA

A

lipophilic ring end so can diffuse through membrane
hydrophilic end to bind to Na channel
middle intermediate chain with either ester or amide. We use amide LA

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2
Q

how does LA work?

A

by reversibly blocking Na+ channels which blocks the action potential

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3
Q

what are the two theories as to how LA works?

A

membrane expansion theory
specific receptor theory

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4
Q

what is the membrane expansion theory?

A

anaesthetic caught up in the membrane, filling space in the membrane and squashes the channels shut

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5
Q

what is the specific receptor theory?

A

anaesthetic outside the cell must diffuse inside the nerve (hence lipophilic), it will then bind to the inactivation gate in the sodium channel to keep it shut

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6
Q

LA drugs are poorly soluble in aqueous environment. When it is dissolved it exists in 2 states in equilibrium.
what are the two states?

A

uncharged LA
charged LA

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7
Q

explain the path charged and uncharged LA take to bind to Na channels

A

Uncharged LA will go through the membrane into the nerve, it re-equilibrates into a proportion of charged and uncharged in the nerve. Its the charged part that then binds to the channel protein.

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8
Q

how does low pH affect LA using this equation

A

lots of H+ so pushes reaction towards charged LA, less uncharged LA, so less diffuses across membrane, less gets recharged so less binds to sodium channels

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9
Q

name three properties of LA

A

protein binding
vasodilators
lipid solubility

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10
Q

explain the LA property protein binding

A

Binds to large plasma proteins that provide a pool of anaesthetic that is slowly released so increased duration (Bupivicaine and Articaine)

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11
Q

explain the LA property of vasodiltion

A

muscle contraction controlled by electrical signals so Na+ channel blockers relax muscle. Increased blood flow increases uptake so LA wears off faster (least vasodilatory - prilocaine and mepivacaine)

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12
Q

explain the LA property of lipid solubility

A

High lipid solubility will easily pass through nerve membrane so faster onset (articaine has high lipid solubility)

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13
Q

what happens when LA enters the blood stream?

A

its affect is lost
it may enter an organ

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14
Q

which organs are highly perfused and thus likely for LA to enter?

A

brain
liver
kidneys
placenta

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15
Q

how does LA affect the CNS?

A

depresses it

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16
Q

how does LA affect peripheral vessels?

A

vasodilation -> hypotension

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17
Q

how does LA affect the respiratory system?

A

bronchodilation

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18
Q

how does LA affect the myocardium?

A

calms the heart by reducing excitability and conductivity

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19
Q

what are the 3 that LA can metabolise in?

A

plasma
lungs
liver

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20
Q

where is most LA metabolised?

A

liver

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21
Q

where is articaine metabolised? what does this mean?

A

plasma and liver therefore seen safer as has short half life

22
Q

name 3 things vasoconstrictors do

A

extend duration of LA
reduce circulating LA conc.
reduce haemorrhage (bleeding)

23
Q

name 2 vasoconstrictors and their manufacturing name

A

adrenaline - epinephrine
fellypressin - octapressin

24
Q

how does adrenaline (epinephrine) work?

A

Binds to a1 receptors in arterial blood vessels causing vasoconstriction reducing blood flow to and from a tissue

25
Q

its not possible to be allergic to adrenaline, if a patient says they are allergic what is the likely cause?

A

they are allergic to the preservative as adrenaline requires it.

26
Q

how does fellypressin (octapressin) work?

A

Vasoconstriction on venous blood so doesn’t reduce blood flow in only out of tissue so not as good as adrenaline

27
Q

when should fellypressin be avoided? why?

A

Pregnancy: avoid due to mild oxytocic effect (oxytocin given to induce labour)

28
Q

name 4 LA and their manufacture name in order of most used

A

lidocain (lignospan special)
prilocaine (citanest)
mepivacaine (scandonest)
articaine (septanest)

29
Q

what is the anaesthetic in lidocaine?

A

lidocaine hydrochloride

30
Q

what is the vasoconstrictor in lidocaine?

A

adrenaline

31
Q

is there preservative in lidocaine?

A

yes

32
Q

what is the maximum dose per kg and absolute max dose of lidocaine?

A

4.4mg/kg
300mg

33
Q

when is lidocaine used?

A

most of the time

34
Q

when should lidocaine not be used?

A

cardiac conditions
allergy to preservative
tricyclic antidepressants
mono-amine oxdiase inhibitors (antidepressants)

35
Q

what is the anaesthetic in prilocaine?

A

prilocaine hydrochloride

36
Q

what is the vasoconstrictor in prilocaine?

A

fellypressin

37
Q

is there preservative in prilocaine?

A

no

38
Q

what is the maximum dose per kg and absolute max dose of prilocaine?

A

6mg/kg
400mg

39
Q

when should prilocaine be used?

A

Use as alternative to lidocaine to avoid adrenaline or if preservative allergy

40
Q

when should prilocaine not be used?

A

pregnancy

41
Q

which LA is the least vasodilatory?

A

mepivacaine

42
Q

what is the anaesthetic in mepivacaine?

A

mepivacaine hydrochloride

43
Q

what is the vasoconstrictor in mepivacaine?

A

none

44
Q

what is the preservative in mepivacaine?

A

none

45
Q

what is the maximum dose per kg and absolute max dose of mepivacaine

A

4.4mg per kg
300mg

46
Q

when should mepivacaine be used?

A

as alternative to prilocaine

47
Q

what is the vasoconstrictor in articaine?

A

adrenaline

48
Q

is there preservative in articaine?

A

yes

49
Q

when should articaine be used?

A

potentially as alternative to inferior alveolar blocks

50
Q

what cautions do we have to reduce the dose for?

A

liver disease
beta blockers
calcium chain blockers
drug abuse

3 Pain and pain management (12 decks)

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