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Muscular, Derma & Senses > Local Anesthetics 💉 > Flashcards

Local Anesthetics 💉 Flashcards

1
Q

Which sites of the neuron have lots of voltaged gated sodium channels?

A

Note of Ranvier
Gaps in the myelin sheath

Important site for Local anaesthetics

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2
Q

Is the nerve bi-layer filled with lipids?

A

Yes, therefore drugs need to ve lipophilic

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3
Q

How do local anaesthetics work?

A

Reversibly block the never conductance that transmits nociception to the brain

Binds to selective site INSIDE of the voltage gated sodium channel in the excitable membranes of nerve cells

Stops sodium from passing through channels.

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4
Q

What type of conformation do Local Anaesthetics prefer?

A

Activated (open) and inactivated (closed) channels

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5
Q

Pharmacophore of LA?

3 major components

A
  • lipophilic aromatic head
  • linked by either an ESTER or AMIDE chain to the
    -Terminal hydrophobic amine tail
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6
Q

Can the ionised form of LAs penetrate the gate?

A

No. Ionised forms of LA are +ve charged, can’t penetrative the gate but CAN BLOCK THE VOLTAHE GATED NA CHANNEL FROM THE INSIDE

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7
Q

How many carbon atoms in the linkage region of LA provided the ideal banalnce between potency and toxicity?

A

1 to 3 carbons.

= longer/more branched chains have increased potency and increases toxicity

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8
Q

What determines the onset of action of LAs?

pH or pKa?

A

pKa(dissocation factor)

pKa = the pH at whi h 50% of the drug is in the lipid soluble unionised form and 50% are in the water soluble ionised form

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9
Q

Structure- activity relationship:

Does the ionised (BH+) drug or unionised (B+) penetrate the membrane?

A

Unionised (B+) drug penetrates the membrane

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10
Q

Structure activity relationship

Does the ionised BH+ or the unionised B+ block the Voltage gated sodium channel?

A

Unionised B+ penetrated the membrane, it gets converted to ionised inside.

= The ionised BH+ blocks the gate, preventing the influx of Na entering the cell = no action potential = no message of pain

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11
Q

How is the cation-to-base ratio critical to conduction block?

A

Too little base = too few local anaesthetics molecules will reach the neural target

Too little cation to bind to Na channel Receptor sites = Too few Na channels will.be closed to ion traffic

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12
Q

Why are local anaesthetics less effective in infected or inflamed tissues?

A

Infection = acidic environment = greater portion of ionised drug and less local anaesthetic base

= less unionised drug availabile to cross the nerve membrane.

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13
Q

Local anaesthetics with a lower pKa have a:
FASTER OR SLOWER
ONSET OF ACTION?

A

Lower pKa = faster onset of action

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14
Q

What 2 factors are associated with greater potency of LAs?

A
  1. Lipid solubility:
    More lipophilic = greater permiability and affinity
  • lipid solubility determined by aromatic ring, its substituants + substitutions to tertiary amine
  1. Molecular Weight:
    Larger molecule = greater lipid solubility

Eg.
Bupivacaine and Ropivacaine are more lipid soluble than Lidnocaine.

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15
Q

What are concentrations of LAs expressed in (units)?

A

% or mg/mL

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16
Q

Speed of onset

If a LA has a pKa closer to 7.4, does this increase or decrease its onset of action?

A

PKa closervto 7.4 = increases portion of unionised La = more rapid onset

Eg. Lidnocaine (pka 7.8) has a more rapid onset than Bupivacaine (pka 8.1)

17
Q

Does a INCREASE OR DECREASE concentration of solution increase rapid onset?

A

Increase concentration of solution

18
Q

Do smaller or larger molecular Weight increase onset pf action?

A

Smaller mW = faster onset

19
Q

Does High lipid solubility result in sequestration of neighbouring adipose tissue and slower onset?

A

Yes

20
Q

How does site of injection effect speed of action?

A
  • SUBCUT = IMMEDIATE
  • SPINAL = MINUTES
  • PERIPHERAL NERVE BLOCK = longest
21
Q

Metabolism of ESTERS

A

Hydrolysed rapidly in plasma by
PSEUDOcholinesterase OR
PABA (which can cause allergic reactions)

22
Q

Metabolism of AMIDEs

A

Metabolised by liver

23
Q

Is there any cross reactivity between AMIDE AND ESTER groups?

A

No cross-reactivity between the 2 groups

24
Q

Does lipid solubility increase or decrease DURATION of ACTION?

A

LA with higher lipid solubility remains bound to nerve membranes longer snd have higher binding affinity to AAG = LONGER DURATION OF ACTION

25
Q

Name some long acting LAs?

A

Bupivacaine
Ropivacaine

26
Q

Why is Adrenaline co administrated with some LAs?
And how does it help?

A

Vasodilatory effects of LA may promote systemic absorption before anaesthetic reaches the nerve membrane.

ADRENALINE helps over come this by:

  1. Vasoconstriction
  2. Decrease systemic absorption
  3. Increase duration of action and decrease toxicity
27
Q

What are other targets for Local Anesthetics?

A
  1. Voltage gates K and Can channels
  2. B-adrenergic
  3. Nicotine acetylcholine receptors
28
Q

Whilst can ve the cause of hypersensitivity reactions in ESTER LAS?

A

Hypersensitivity common.

Due to PABA metabolite

29
Q

Why are the causes of hypersensitivity reactions on AMIDE LAS?

A

Preservatives

30
Q

What is the LAST (LOCAL ANESTHETIC SYSTEMIC TOXICITY) related to?.

A

Systemic absorption OR
accidental intravascular injection

31
Q

Risk of systemic toxicity is influenced by?

A

Dose and Patient Factors

32
Q

Name some LAs 7

A
  1. Lignocaine (Lidnocaine)
  2. Amethocaine (Tetracaine)
  3. Cocaine
  4. Buprivacaine
  5. Ropivacaine
  6. Epidural
  7. Spinal anaesthia
33
Q

Which LAS are AMIDES

(RBL)s

A

Lignocaine (lidnocaine)
Bupivocaine
Ropivacaine

(RBL)

34
Q

Which LAS are ESTERS

2
AC

A

Amethocaine ( tetracaine)
Cocaine

35
Q

Use of

LIGNOCAINE (LIDNOCAINE)

A

Short duration procedures

36
Q

Use of

AMETHOCAINE
(TETRACAINE)

A

Restricted to topical applications (high systemic absorption)

37
Q

Use of

COCAINE

A

Topical anaesthesia for ENT procedures

Vascontricts blood in nose

38
Q

Uses of

bupivacaine

A

Nerve block, epidural and spinal anaesthia

39
Q

Use of

Ropivacaine

A

Nerve block, epidural

Muscular, Derma & Senses (20 decks)

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