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Pharmacology Drugs > Anti-epileptics > Flashcards

Anti-epileptics Flashcards

1
Q

What are examples of Benzodiazepines?

A
  • Lorazepam
  • Midazolam
  • Diazepam
  • Clonazepam
  • Sodium Valproate
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2
Q

What is the mechanism of action of benzodiazepines?

A

Act at distinct receptor site on GABA chloride channel. Act as positive allosteric effects. Enhancement of GABA action through:

  • Inhibition of GABA inactivation
  • Inhibition of GABA re-uptake
  • Increase rate of GABA synthesis

This increase chloride current into the neurone which increases the threshold for action potential generation. There is therefore a decreased chance of reaching the seizure threshold

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3
Q

What are the uses of Benzodiazepines?

A

Used in emergency as first line therapy for acute life-threatening status epilepticus or any acute seizures that has not terminated in 5 mins

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4
Q

How is Lorazepem used?

A

IV bolus 4mg is first line in emergency such as status epilepticus

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5
Q

How is diazepam used?

A

Can be given rectally if no access in status epilepticus

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6
Q

How is Midazolam used?

A

Buccal if no IV access in emergency

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7
Q

How is Clonazepam used?

A

-Absence seizure in the short term

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8
Q

Describe the pharmacokinetics of Benzodiazepines?

A

-Well absorbed 90-100% highly plasma bound 85-100%

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9
Q

What are the side effects of Benzodiazepines?

A
  • Sedation
  • Tolerance with chronic use
  • Confusion impaired co-ordination
  • Aggression
  • Dependence/Withdrawal with chronic use
  • Abrupt withdrawal seizure trigger
  • Respiratory and CNs depression
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10
Q

What are some drug interactions of Benzodiazepines?

A

-Some adjunctive use

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11
Q

How is benzodiazepine overdose reversed?

A

Overdose reversed by IV flumazenil, but its use may precipitate seizure/arrhythmia

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12
Q

What are examples of sodium channel blockers?

A
  • Lamotrigine
  • Phenytoin
  • Carbamazepine
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13
Q

What is the mechanism of action of sodium channel blocker?

A
  • Inhibition of voltage gated sodium channels function by binding during depolarisation -hence voltage dependant
  • Prolongs inactivation state so cant stimulate another action potential. this is to bring the firing rate back to normal
  • Reduces probability of high abnormal spiking (firing lots of action potentials)
  • Once neurone membrane potential back to normal VGSC blocker detaches from binding
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14
Q

How is phenytoin used?

A
  • Used for generalised Tonic-Clonic and all partial.

- Used in emergency as a loading dose + infusion when seizure not terminating after 10 mins

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15
Q

How is Carbamazepine used?

A

-First line therapy for partial seizures (or generalized tonic-clonic seizures).

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16
Q

What is the pharmacokinetic properties of Carbamezipine?

A
  • Strong CYP450 ENZYME INDUCER: increases its own metabolism with repeated doses reducing its half-life from 30 hr to 15 hr
  • Well absorbed and 75% protein bound - Linear PK
  • Contraindicated with AV conduction problems
17
Q

How is Lamotrigine used in practice?

A
  • Lamotrigine is the drug of choice for women of childbearing age as LEAST teratogenic
  • Lamotrigine is used increasingly as first line
18
Q

What are some general ADRs of Carbamezipines?

A

General: Dizziness, Drowsy, Ataxia, Motor Disturbance, Numbness, Tingling, GI upset, Vomiting, Variation in BP, Rashes, Hyponatraemia

Rare: neutropenia

19
Q

What are the pharmacokinetics of Phenytoin?

A
  • CYP450 inducer
  • Well absorbed - but 90% bound in plasma competitive binding can increase levels
  • NON LINEAR pharmacokinetics at therapeutic levels so close dose monitoring required. Patients will have a chart and graph to work out dosing.
20
Q

What are the ADRs associated with phenytoin?

A
  • Gingival Hyperplasia (20%)
  • Rashes or hypersensitivity. (Steven Johnson in 2-5%)
  • CNS symptoms such as Dizziness, Ataxia, Headache, Nystagmus, Nervousness
21
Q

What are the pharmacokinetics of Lamotrigine?

A
  • Well absorbed - Linear PK. Half-life is 24 hours

- No CYP450 induction so fewer DDIs

22
Q

What are the ADRs associated with Lamotrigine?

A
  • Less marked CNs dizziness, ataxia and somnolence
  • Nausea
  • Some mild and serious skin rashes
23
Q

What are some drug interactions of Carbamezepines?

A
  • Decreases the effect of many drugs: Warfarin, Systemic Corticosteroids, Oral Contraceptives, Phenytoin
  • Contraindicated use with Antidepressants such as SSRIs, MAOIs, & TCA as they interfere with action of Carbamazepine

Adjust Dosing

24
Q

What are some drug interactions of Phenytoin?

A
  • Competitive binding eg with Valproate, NSAIDS/salicylate Increases plasma level exacerbating Non-Linear PKs
  • Decreases the effect of Oral contraceptive
  • Increases Cimetidine action
25
Q

What are some drug interactions of Lamotrigine?

A

Adjunct therapy with other AEDs

  • Oral contraceptive reduce the LTG plasma levels
  • Valproate increase LTG in plasma due to competitive binding
26
Q

What is the mechanism of action of Sodium Valproate?

A

Mixed sites of Action - Pleiotropic

  • Weak inhibition GABA inactivation enzymes increasing GABA
  • Weak stimulus of GABA synthesising enzymes increasing GABA
  • VGSC blocker + Weak Ca2+ channel block so discharge
27
Q

How is sodium valproate used in practice?

A

-First line therapy for primary generalized seizures, (Tonic+Clonic, Absence, Partial Seizures)

28
Q

What are the pharmacokinetic properties of Sodium Valproate?

A
  • Pharmacokinetics:

- Absorbed 100% - then 90% plasma bound Linear PK t1/2 = 15 hrs

29
Q

What are some ADRs of Sodium Valproate?

A
  • MOST teratogenic and can lead to sodium valproate syndrome
  • Generally less severe ADRs than with other AEDs
  • CNS sedation ataxia tremor - weight gain
  • Hepatic function affected resulting in elevated Transaminases in 40% patients
  • Rarely - hepatic failure
30
Q

What are the emergency seizure management procedures?

A
  • A to E approach - protect airway, recovery position, give oxygen
  • Try benzodiazepines first: either buccal midazolam, IV lorazepam or rectal diazepam
  • If not terminating 5 mins later give a further dose
  • If still not terminating e.g. have been having a seizure for 10-15 mins then CALL ITU + MED Specialist Registrar and give loading dose of IV phenytoin.

Pharmacology Drugs (22 decks)

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