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Pharmacology > 13 - Local Anaesthetics > Flashcards

13 - Local Anaesthetics Flashcards

1
Q

Anaesthetics are drugs that…

A

Prevent pain for a limited period of time

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2
Q

Anaesthetics are divided into two main categories…

A
  • Local (prevents local pain/ nociception)
  • General (induces a loss of consciousness)
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3
Q

Analgesics are drugs that…

A

Reduce (rather than prevent) pain

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4
Q

Local anaethetics work by blocking…

A

Electrical signalling in neurones

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5
Q

How do local anaesthetics block electrical signalling in neurons?

A

By blocking voltage gated sodium channels

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6
Q

Sodium Channels are made up of 3 subunits, namely…

A

α, β1 & β2

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7
Q

The α subunit of the sodium channel is a ______ polypeptide with ___________ domains and 4 _________ domains and 6 _-_____ regions.

A

The α subunit of the sodium channel is a single polypeptide with extracellular domains and 4 transmembrane domains and 6 α-helical regions.

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8
Q

The beta subunits of the sodium channel anchor the…

A

Alpha subunit within the phospholipid membrane

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9
Q

The ( beta 1 / beta 2 ) subunit is ( covalently / ionically) bonded to the alpha subunit.

A

The beta 2 subunit is covalently bonded to the alpha subunit.

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10
Q

The voltage gate sodium channel has voltage sensors located in the…

A

Hydrophobic domains of the alpha subunit

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11
Q

It is thought that local anaesthetics exert their effect by…

A

Physically plugging the transmembrane pore of the sodium channel

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12
Q

Ionised molecules can’t cross lipid membranes. Why is this a problem for a local anaesthetic?

A

Local anaesthetic molecules bind in an ionised form. But the binding site in at the inner end of the ion channel, which requires intracellular access!

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13
Q

The ideal local anaesthetic enters in an (ionised / un-ionised) form through the axon membrane. This converts to an (ionised / un-ionised) form which binds to the channel.

A

The ideal local anaesthetic enters in an un-ionised form through the axon membrane. This converts to an ionised form which binds to the channel.

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14
Q

Describe the general structure of anaesthetic molecules…

A
  • Aromatic group (ensures lipid solubility)
  • Ester or amide group
  • Basic amine side-chain (ensures ionisation at lower pH)
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15
Q

The duration of action of local anaesthetics is limited by which two factors?

A
  • Lipid solubility
  • Hydrolysis of the ester/amide bond
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16
Q

Esters are metabolised by ________ (with the exception of _________ )

A

Esters are metabolised by esterases (with the exception of cocaine )

17
Q

Amides are metabolised by ________ in the ______* . This gives anaesthetics linked by an amide group a longer half life, but poses consequences for those with _____ *________.

*same word

A

Amides are metabolised by CYP3A4, 1A2 in the liver. This gives anaesthetics linked by an amide group a longer half life, but poses consequences for those with liver failure.

18
Q

Process of local anaesthesia…

A
  1. Anaesthetic injected as hydrochloride salt in acid solution
  2. Drug dissociates releasing lipid-soluble free base (due to higher pH)
  3. Lipid soluble free base enters axon
  4. Re-ionisation in the axon (due to lower pH)
  5. Re-ionised molecule enters and blocks sodium channels
  6. Depolarisation prevented
19
Q

Coadministration of adrenaline with a local anaesthetic can be used to achieve which 2 effects?

A
  • Restrict the site of action
  • Prolong duration of action

(due to local vasoconstriction via α1 adrenoreceptors)

20
Q

What method can be used to accelerate the speed of onset of a local anaesthetic?

A

Using a slightly alkaline solution to improve absorption into nerve tissue

21
Q

Different axon types show different sensitivities to local anaesthetics.

Local anaesthetics are more effective in which of the following fibres (and why?):

Nosciceptive fibres

Motor axons

A

Nosciceptive fibres as they are small, whereas motor axons are larger and less sensitive

22
Q

Use-dependent block

A

Depth of block increases with the frequency of action potentials (as access and affinity are improved when the channel is open)

23
Q

Unwanted side effects of local anaesthetic are generally caused by…

A

The drug escaping into systemic circulation

24
Q

Unwanted CNS side effects of local anaesthetics include…

A

Confusion and agitation

25
Q

Unwanted cardiovascular side effects of local anaesthetics include…

A

Hypotension (due to inhibition of sympathetic activity, inhibition of sodium conductance in cardiac tissue)

26
Q

A limitation of local anaesthetics is that they are not very effective in ________ or _________ tissue

A

A limitation of local anaesthetics is that they are not very effective in infected or inflammed tissue

27
Q

Tetrodotoxin is produced by marine bacteria and is utilised by frogs, newts and pufferfish. It works by…

A

Blocking voltage-gate sodium channels

28
Q

The nervous system comprises of sensory neurons detecting input, interneurones in the CNS responsible for _________ and finally output via the PNS and glands

A

The nervous system comprises of sensory neurons detecting input, interneurones in the CNS responsible for integration and finally output via the PNS and glands

29
Q

List the chemical drug targets in the nervous system (6)…

A
  • G-protein coupled receptors
  • Ligand gated ion channels (ionotropic receptors)
  • Enzyme linked (kinase) receptors
  • Synthesis of NT
    Reuptake of NT
  • Release of NT
30
Q

Other than local anaesthetics, give 2 examples of drug types that target voltage-gated ion channels…

A
  • Antihypertensive and antiarrythmic drugs (L-type calcium channels)
  • Anticonvulsant/ antiepileptic drugs (Sodium channels)
31
Q

Give two examples of anticonvulsant/antiepileptic drugs and state how they exploit use-dependent block…

A

Phenytoin and carbomazepine

Use-dependent block allows these drugs to block high frequency discharges (corresponding to seizures) while allowing normal frequency firing.

32
Q
A

Pharmacology (23 decks)

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