Antiepileptics Flashcards

1
Q

Glutamate

  • function
  • receptors
  • mechanism
A
  • excitatory neurotransmitter
  • NMDA, AMPA, etc
  • AP > Na+ mediated Ca2+ influx > depolarization and vesicle release
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2
Q

GABA

  • function
  • receptors
  • mechanism
  • recycling
A
  • inhibitory neurotransmitter
  • GABA a receptor
  • binds to receptor > Cl- influx > counteract depolarization
  • recycling: converted to SSA by GABAT (transaminase)
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3
Q

What are the 3 mechanisms of AEDs?

A
  • Na+ and Ca2+ channel inhibition
  • Enhancement of GABA activity
  • Inhibition of glutamate activity
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4
Q

Name the Na+ and Ca2+ channel modulators

A
  • carbamazepine
  • phenytoin
  • lamotrigine
  • valproate (also a GABAT inhibitor)
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5
Q

Name the GABA enhancers

A
  • Benzodiazepines
  • vigabatrin
  • valproate
  • Levetiracetam
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6
Q

6 properties of benzodiazepines

A
  1. Anxiolytic
  2. Sedative
  3. Hypnotic
  4. Muscle relaxant
  5. Anti-convulsant
  6. Amnesic
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7
Q

Mechanism of action of benzos

A
  • increase the frequency of Cl- channel opening in the GABA receptor when the GABA is present (increased affinity)
  • Increased Cl- within the cell increases
    its resistance to depolarization
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8
Q

Benzos used in epilepsy

A
  • diazepam
  • midazolam
  • lorazepam
  • clobazam
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9
Q

Phenytoin

A

Phenytoin
• Causes hyperpolarization via sodium channels (blocks inactive sodium channels)
• Displays zero-order kinetics (metabolised at constant rate irrespective of plasma concentrations)
• Narrow therapeutic index
• CYP450 Enzyme inducer
• teratogenic

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10
Q

Phenytoin - side effects

A
  • confusion
  • gum hyperplasia, acne, hirsutism
  • ataxia, nystagmus
  • rashes to severe recations
  • haematological/ anaemia
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11
Q

What are the drugs that lower seizure threshold (reduce AED efficacy)

A
  • SSRIs
  • TCAs
  • antipsychotics
  • tramadol
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12
Q

Sodium valproate - mechanism

A
  • Both a sodium channel blocker and GABA transaminase inhibitor
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13
Q

Sodium valproate - side effects

A
  • GI upset
  • weight gain
  • tremor, ataxia, behavioural
  • thrombocytopenia and increased LFTs
  • hair loss
  • teratogenic
  • SIADH, hyponatremia
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14
Q

What birth defects can occur in foetal valproate syndrome?

A
  • spina bifida
  • Facial and skull malformations (including cleft lip and palate)
  • congenital heart defects eg VSD
  • gastroschisis
  • hypospadias with undescended testes
  • limb abnormalities
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15
Q

carbamazepine - mechanism and ADRs

A
  • inhibit neuronal Na+ channels

- ADRs: GI upset, dizziness/ataxia, mild maculopapular rash, SIADH/hyponatremia/oedema

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16
Q

Levetiracetam

A
  • Binds synaptic vesicle glycoprotein 2A and inhibits presynaptic calcium channels
  • ADRs behavioural (suicidal ideation risk doubling)
17
Q

Vigabatrin

A
  • inhibitor of gamma-aminobutyric acid aminotransferase (GABA-AT), the enzyme responsible for the catabolism of GABA. So increases GABA levels
  • can cause visual field defects
  • common ADRs: Abdominal pain; anaemia; anxiety; arthralgia; behaviour abnormal
18
Q

Which AEDs are not safe in pregnancy

A

Least safe to safest:

  • valproate
  • phenytoin
  • lamotrigine