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4 - CPT > Anti-Epileptic Drugs > Flashcards

Anti-Epileptic Drugs Flashcards

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1
Q

What is the general criteria in determining whether a patient is epileptic

A

Diagnosis requires evidence of recurrent seizures unprovoked by other identifiable causes

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2
Q

Define epilepsy

A
  • Episodic discharge of abnormal high frequency electrical activity in brain leading to seizure
  • Mismatch between excitation and inhibition of neurotransmitters
  • Spread of neuronal hyperactivity from small group of neurones
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3
Q

Describe partial seizures

A
  • Simple - conscious
  • Complex - impaired consciousness due to spreading of seizures
  • Secondary generalised seizures - loss of consciousness
  • Symptoms reflex area affected - eg. Involuntary motor disturbances, behavioral change, aura
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4
Q

Describe generalised seizures

A
  • Generated centrally and spreads through both hemispheres with loss of consciousness
  • Tonic-clonic seizures - 60% of generalised seizures
  • Absence seizures - common in children
  • Others include: tonic, myoclonic, atonic
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5
Q

Describe status epilepticus

A
  • Seizures which prolong beyond 5 minutes or series of seizures without recovery interval
  • Untreated can lead to brain damage or death
    • Hypoxia due to decreased respiratory function and interrupted breathing
    • Cognitive impairment
    • Physical injury relating to fall/crash
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6
Q

What are primary causes of epilepsy

A
  • Idiopathic (65-70%)

- May be due to channelopathies - damage to ion channels and the protein which regulates them

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7
Q

What are secondary causes of epilepsy

A
  • Medical conditions affecting (30-35%)
  • Vascular disease, head injury, tumours, infection, hypoglycaemia
  • In elderly, secondary causes account for 60% of their seizures
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8
Q

Describe some of the major recognized precipitants of epilepsy

A
  • Sensory stimuli
    • Flashing lights/strobes
  • Brain disease / trauma
    • Brain injury
    • Stroke / haemorrhage
    • Drugs / alcohol
    • Structural abnormality / lesion
  • Metabolic disturbances
    • Hypoglycaemia, hypocalcaemia, hyponatraemia
  • Infections
    • Febrile convulsions in infants (seizure due to fever)
  • Therapeutics
    • Some drugs can lower electrical threshold - easier to potentiate
      • Anti-depressants
    • AEDs and polypharmacy
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9
Q

State the major drug classes and examples to treat epilepsy

A
  • Voltage gated sodium channel blockers
    - Carbamazepine
    - Phenytoin
    - Lamotrigine
  • Enhancing GABA mediated inhibition
    - Valproate
    - Benzodiazepine
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10
Q

Describe the mechanism of voltage gated sodium channel blockers

A
  • Drugs bind inside channel and cause the channel to be locked in the inactivated state, thus sodium cannot pass through
  • Reduce the probability of high abnormal spiking activity
  • VGSC only bind to target site during depolarisation - voltage dependent
  • Prolongs inactivation state - firing rate back to normal
  • Once neurone membrane potential returns back to normal, VGSC blocker detaches from binding site
    - Self regulating - need to treat epilepsy without stopping homeostatic neuronal activity
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11
Q

Describe the ADRs of carbamazepine

A
  • CNS: dizziness, drowsy ataxia, motor disturbance, numbness, tingling
  • GI - upset vomiting
  • CV - cause variation in BP
    • Contraindicated with AV conduction problems
  • Rashes
  • Hyponatraemia
  • Severe bone marrow depression - neutropenia (rare)
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12
Q

Describe the DDis of carbamazepine

A
  • CYP450 inducer can affect many other drugs
  • Decrease phenytoin leading to increase carbamazepine plasma concentration
  • Decrease warfarin, systemic corticosteroids, oral contraceptives concentration
  • Antidepressants - SSRI, MAOI, TCA interfere with action of carbamazepine
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13
Q

Why are carbamazepine and phenytoin not used in absence seizures

A
  • Not Ca channel blockers and therefore do not resolve absence seizures
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14
Q

List the ADRs of phenytoin

A
  • CNS: dizziness, ataxia, headache, nystagmus, nervousness
  • Gingival hyperplasia (increase gum size)
  • Rashes - hypersensitivity, Stevens Johnson
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15
Q

Describe the DDIs of phenytoin

A
  • CYP450 inducer
  • Competitive binding with valproate, NSAIDs/ salicylate increases plasma levels and exacerbates non-linear PK
  • Decrease oral contraceptive effectiveness - avoid giving to young females
  • Increase cimetidine and phenytoin concentration
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16
Q

Describe the ADRs of lamotrigine

A
  • Less marked CNS dizziness, ataxia, somnolence (sleepiness)
  • Skin rashes - common in children
  • Not used first line in paediatrics
17
Q

Outline how GABA can act as an anticonsulvant

A
  • GABA is a natural anticonvulsant or excitatory ‘brake’
  • When drugs bind to GABA receptor, it allows chlorine to pass through and thus hyperpolarising tissue
    • Increases threshold for action potential generation
    • Reduces likelihood of epileptic neuronal hyperactivity
  • GABA can be increased through inhibition of GABA inactivation, inhibition of GABA re-uptake and increased rate of GABA synthesis
18
Q

Explain the mechanism of valproate

A
  • Weak inhibition of GABA inactivation enzymes and weak stimulus of GABA synthesizing enzymes
  • VGSC blocker and weak Ca channel blocker decrease neuronal discharge
19
Q

List the ADRs of valproate

A
  • VALPROATE
  • Very teratogenic - sodium valproate syndrome
  • Vomiting
  • Alopecia
  • Liver toxicity - increase hepatic function transaminases
  • Pancreatitis/pancytopenia
  • Retention of fats - weight gain
  • Oedema
  • Anorexia
  • Tremor
  • Enzyme inhibitor
20
Q

What are contra-indications of valproate

A
  • Pregnancy
  • Depression
  • COCP
  • Liver problems
  • Pancreatitis
21
Q

Explain the mechanism of benzodiazepines

A
  • Act to increase GABA chloride channel
  • Binding of GABA or BZD enhance each others binding - act as positive allosteric effectors
  • Increasing chloride current into neurone increases threshold for action potential generation
22
Q

List the ADRs of benzodiazepines

A
  • Not used long term due to many ADRs
  • Sedation
  • Tolerance with chronic use (addiction)
  • Confusion, impaired coordination
  • Aggression
  • Dependence/withdrawal with chronic use
  • Abrupt withdrawal seizure trigger
  • Respiratory and CNS depression
23
Q

Describe safe prescribing rules of anticonvulsants

A
  • Monotherapy is optimal aim to minimise side effects - change up to 3 AEDs before thinking of alternative treatment such as surgery
  • Aim to start at low dose and increase slowly - want to achieve seizure control at lowest possible dose to avoid side effects
  • Monitor and titrate to therapeutic effect as significant variation in AED plasma levels
  • Drug interactions common as many AEDs plasma bound and some metabolised by CYP450
24
Q

Describe the safety concern of anticonvulsant therapy in pregnancy

A
  • Need to balance risk of epilepsy in the mother vs AED teratogenicity
  • Consider if the mother has severe epilepsy due to not taking AED, then the baby’s prognosis will not be good as mother will have respiratory problems
  • Use single AED agent if possible at lowest dose
    • Valproate best avoided due to neural tube defects
  • Lamotrigine safest AED
  • Give folate supplement preferably before conception to reduce risk of neural tube defect
  • AEDs associated with vitamin K deficiency in newborn - coagulopathy and cerebral haemorrhage
    • Vitamin K supplement given in last trimester
25
Q

Appreciate the value of therapeutic drug monitoring in phenytoin therapy

A
  • Close monitoring of free plasma concentration needed
    • Can be taken from salivary levels as an indicator
  • Phenytoin has non-linear PK at therapeutic levels, thus concentration can drastically change
    - Increased risk of overdose / toxic doses
26
Q

Describe the management of complex partial seizures

A
  • Carbamazepine
  • Increase dose or chance to valproate
  • After discontinuing and change up to 3 drugs, try surgical measures such as lobectomy of area where seizure originating from
27
Q

Describe the management of absence seizure

A
  • Valproate preferably

- Give lamotrigine if valproate is unsuitable

28
Q

Describe the management of tonic clonic seizure

A
  • Valproate preferably

- If valproate not suitable (pregnant, COCP), then give lamotrigine

29
Q

Describe the management of status epilepticus

A
  • A to E approach - airways, breathing, circulation, disability, exposure
    • Exclude hypoglycaemia (could cause seizure)
  • Benzodiazepines given after 5 minutes - IV, rectal, buccal
  • Further benzodiazepine dose
  • Phenytoin IV given as loading dose + infusion if seizure not terminated after 10 minutes
  • Call ITU
  • Anaesthesize them if seizure lasts for long time

4 - CPT (23 decks)

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