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Pharmacology > Anti-epileptic drugs > Flashcards

Anti-epileptic drugs Flashcards

1
Q

What is epilepsy

A

Chronic disorder characterised by recurrent episodes of seizures

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2
Q

What is the pathophysiology of epilepsy

A

Increased excitatory activity
Decreased inhibitory activity
Loss of control of neuronal membrane potential
Neurones heavily Depolarise and increased rate of discharge
Spread of hyperactivity by synaptic transmission

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3
Q

What are the types of epilepsy

A

Partial:
Simple
Complex
Secondarily generalised

Generalised:
Tonic clonic
Absence

Status epilepticus

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4
Q

What are the causes of epilepsy

A 
Primary: idiopathic, 70%
Secondary to Brain damage: 
Head injury 
Asphyxia
Infection 
Stroke/haemorrhage 
Malignancy
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5
Q

What are precipitants of epilepsy

A 
Sensory: flashing lights
Alcohol
Drugs
Stroke/haemorrhage 
Metabolic: hypo/hyperglycaemia, hypo/hypernatraemia
Infections
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6
Q

What are main therapeutic targets of antiepileptic drugs

A

Inhibition of Voltage gated Na channels

Enhance GABA-mediated inhibition

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7
Q

What are the types of VG Na Channel inhibitors

A

Carbamazepine
Lamotrigine
Phenytoin

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8
Q

What is mechanism of action of VG Na channel inhibitors

A

Inhibit INACTIVE VG Na channels
Prolong inactive state
Preferentially act on neurones with high frequency depolarisation + discharge
Due to higher proportion of inactive Na channels
Reset rate of discharge in neurones with high rate of discharge

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9
Q

What are PK properties of carbamazepine

A 
Protein binding 70%
CYP450 inducer 
Induces own metabolism
Starting T1/2 30hr 
Repeated use T1/2 15hr 
Linear PK
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10
Q

What are side effects of carbamazepine

A 
Dizziness, drowsiness, ataxia, numbness
Vomiting
Variation in BP 
Rash
Neutropenia
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11
Q

What are DDIs of carbamazepine

A 
CYP450 induction - raises levels of:
Warfarin
Phenytoin 
Oral contraceptives 
Corticosteroids

Reduced activity with Antidepressants

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12
Q

What monitoring is required with Carbamazepine

A

Adjust dose to therapeutic effect

Due to decreasing T1/2 with repeated use

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13
Q

What are indications of carbamazepine

A

All partial seizures
Tonic clonic seizures
Not absence seizures

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14
Q

What are PK properties of phenytoin

A

Protein binding 90%
CYP450 inducer
Non linear PK at therapeutic dose
Variable T1/2

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15
Q

What are side effects of phenytoin

A

Dizziness, headache, ataxia, nystagmus
Gingivial hyperplasia
Rash
Stevens Johnson syndrome

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16
Q

What are DDIs of phenytoin

A

Increased phenytoin levels (PK binding) with:
NSAID
Valproate
Salicylate

Decrease oral contraceptive levels (CYP450)

Increased phenytoin levels w Cimetidine

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17
Q

What drug monitoring is required with phenytoin

A

Free plasma concentration levels

Salivary levels - indicator for plasma levels

18
Q

What are indications for phenytoin

A

All partial seizures
Tonic clonic seizures
Not absence seizures

19
Q

What are PK properties of lamotrigine

A

Linear PK

Not CYP450 inducer

20
Q

What are side effects of lamotrigine

A

Dizziness, ataxia
Nausea
Rash
(Fewer SEs)

21
Q

What are DDIs of lamotrigine

A

Adjunct to other AEDs
Reduced activity LTG with oral contraceptives
Potentiation of LTG with valproate
(fewer DDIs)

22
Q

What are indications of Lamotrigine

A

All partial seizures
Tonic clonic seizures
Absence seizures

AED of choice for women of child bearing age
Not first line for children (increased rate of SEs)

23
Q

What is mechanism of action of AEDs enhancing GABA-mediated inhibition

A

GABA agonists:
Positive allosteric binding at GABA receptors
At benzodiazepine binding site
Enhance GABA activity at receptor

Affect GABA metabolism:
Activate GABA synthesising enzymes
Inhibit GABA re-uptake enzymes
Increase GABA levels

24
Q

How does GABA activity mediate inhibition

A

GABA is a natural anticonvulsant
40% synapses in brain are GABA-ergic
GABA receptor is Cl channel causing hyperpolarisation

25
Q

What is mechanism of action of valproate

A

Affects GABA metabolism:
Inhibit GABA reuptake
Activate GABA synthesis

26
Q

What are PK properties of valproate

A

90% protein bound

Linear PK

27
Q

What are side effects of valproate

A

CNS - ataxia, tremor, sedation

Hepatic - raised transaminases, hepatic failure

28
Q

What are DDIs of valproate

A

Around Adjunct therapy w other AEDs
Decreased valproate activity w antidepressants
Decreased valproate activity w antipsychotics
Potentate valproate activity w aspirin (PK binding)

29
Q

What drug monitoring is required with valproate

A

Free plasma conc levels

Salivary levels

30
Q

What are indications of valproate

A

All partial seizures
Tonic clonic seizures
Absence seizures

31
Q

What is mechanism of action of benzodiazepines

A

GABA receptor agonist
Bind to Benzodiazepine binding site on GABA receptors
Enhance GABA activity

32
Q

What are PK properties of benzodiazepines

A

90% protein bound

Linear PK

33
Q

What are side effects of benzodiazepines

A 
Confusion
Sedation
Tolerance (long term use)
Dependence + withdrawal (long term use)
Rebound seizure with abrupt withdrawal 
Resp + CVS depression
34
Q

What are DDIs of benzodiazepines

A

IV flumazenil causing rebound seizure

35
Q

What are indications of benzodiazepines

A

Status epilepticus: lorazepam, diazepam

Absence seizure: clonazepam - short term

36
Q

What are prescribing rules of antiepileptic drugs

A

Monotherapy is the aim
Drug choice dependent on patient + condition
If first line ineffective, Switch to another AED before starting combination therapy
Patient must remain under review
Start at low dose + titrate to therapeutic effect
Significant seizures can be treated by sedation + paralysis + intubation in ITU

37
Q

What are general indications of anti epileptic drugs

A

First line for generalised: valproate
First line for partial: carbamazepine
First line for women of CBA: lamotrigine
First line for Status epilepticus: lorazepam

38
Q

What are prescribing rules for women of child bearing age

A

Balance risk of seizure + teratogenic risk of drug

Assess individual: severity/frequency of seizure, history of status epilepticus

39
Q

What are the risks of medication to foetus

A

Phenytoin + carbamazepine:
Increased failure rate of conception

Valproate:
Neural tube defects
Neuro developmental defects - autism, learning disability

Any AEDs:
Increased risk of birth defects
Congenital malformations
Facial/digital hypoplasia

40
Q

What are prescribing rules for pregnant women

A 
Aim for Monotherapy 
Lowest dose 
Lamotrigine is safest
Avoid valproate 
Prescribe Folate supplements (NTDs)
Prescribe Vit K supplements in last trimester: AEDs associated with vitamin K deficiency in newborn
41
Q

What is management of Status Epilepticus

A

ABC
Exclude hypoglycaemia
1st line: IV lorazepam (preferred to diazepam due to longer T1/2 so better control)
2nd line: IV Phenytoin (cardiac monitoring needed)
Sedation + Paralysis + Intubation at ITU if above fails

Pharmacology (19 decks)

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