Session 12 Flashcards
- Definition of Epilepsy
- Diagnosis requires evidence of ?
- Episodic discharge of abnormal high frequency electrical activity in brain leading to seizure
- recurrent seizures unprovoked by other identifiable causes
What causes Epilepsy? (4)
Increased Excitatory Activity
Decreased Inhibitory Activity
Loss of Homeostatic Control
Spread of Neuronal Hyperactivity
Classification of Epilepsy
Two main types:
- Partial seizures
- Generalised seizures
Classification of Epilepsy
Partial (or focal) seizures
Simple (conscious)
Complex partial seizures (impaired consciousness)
Secondary generalised seizures
Loss of local excitatory/inhibitory homeostasis
Increased discharges in focal cortical area
Partial (or focal) seizures
Symptoms reflect area affected eg
- Involuntary motor disturbance
- Behavioural change
- Impending focal spread accompanied by ‘Aura’ eg unusual smell or taste, déjà vu / jamais vu
- May become secondarily generalised
- What are Generalised seizures?
- Give examples
- Generated centrally spread through both hemispheres with loss of consciousness
- Tonic-clonic seizures (Grand mal) – 60%
Absence seizures (Petit mal) – 5%
Many other types /sub types recognised
- Most seizures are short lived ( up to ?)
- Some seizures prolonged beyond this or experienced as series of seizures without recovery interval. Referred to as ?
- What type of epilepsy can SE occur in?
- Prolonged seizure treated as a Medical Emergency. Untreated Status Epilepticus can lead to ?
- 5 mins
- Status Epilepticus
- Any
- brain damage or death (SUDEP)
Dangers in Severe Epilepsy
Uncontrolled epilepsy is not a benign condition: what general effects does it have?
- Physical injury relating to fall/crash
- Hypoxia
- SUDEP – sudden death in epilepsy
- Varying degrees of brain dysfunction/damage
- Cognitive impairment
- Serious psychiatric disease
- Significant adverse reactions to medication
- Stigma / Loss of livelihood
Etiology of Epilepsy
- What do we mean by this is primary epilepsy?
- What do we mean by this is secondary epilepsy?
- What is the likely etiology of epilepsy in the elderly?
- No identifiable cause – idiopathic (65-70%)
Channelopathies ?
- Secondary Medical conditions affecting brain (30-35%)
Vascular disease
Tumours
- In the elderly (60+) secondary responsible for 60% of seizures – important diagnostic
Precipitants
MIST B
Sensory stimuli: eg flashing lights/strobes or other periodic sensory stimuli
Brain Disease/ Trauma: Brain Injury Stroke / Haemorrhage Drugs/Alcohol Structural abnormality/Lesion
Metabolic disturbances: Hypo - glycaemia/calcaemia /natraemia
Infections Febrile convulsions in infants
Therapeutics Some drugs can lower fit threshold AEDs + Polypharmacy: PKs lower levels
Therapeutic Targets for AEDs (2)
- Voltage Gated Sodium Channel Blockers
- Enhancing GABA Mediated Inhibition
VGSC blockers - mechanism of action
Bind to domain 4
VGSC Blockers reduce probability of high abnormal spiking activity
- Local loss of membrane potential homeostasis starts at focal point
- Relatively small number of neurones form generator site
- Neurones heavily depolarise
- Hyperactivity spreads via synaptic transmission to other neurones
Where/when do VGSC blockers bind?
Effect of binding?
When does it detach?
With VGSC Blocker – gets access to binding site only during depolarisation - hence voltage dependent!
Prolongs inactivation state – firing rate back to normal
Once neurone membrane potential back to normal VGSC. Blocker detaches from binding site.
VGSC blockers 1: Carbamezepine
- Pharmacology/ Mechanism of action: ?
- Pharmokinetics:
- ADRs
- DDIs
- Why must we monitor?
- Epilepsy types treated with Carbamezepine
- Carbamezepine prolongs VGSC inactivation state
- Well absorbed 75% protein bound – Linear PK
Initial t 1/2 = 30 hrs but strong inducer of CYP450.
Affects its own Phase 1 metabolism
Repeated use t 1/2 = 15hrs
- Wide ranging Type As:
CNS - dizziness drowsy ataxia motor disturbance numbness tingling
GI - upset vomiting
CV – can cause variation in BP Contraindicated with AV conduction problems
Others: Rashes Hyponatraemia
Rarely Severe bone marrow depression – neutropenia
- Because CYP450 inducer can affect many other drugs
Phenytoin (AED) decrease + PK binding - CBZ plasma conc increase
Warfarin decrease
Systemic Corticosteroids decrease
Oral contraceptives decrease
Antidepressants - SSRIs MAOIs TCAs & TCA interfere with action of Carbamezepine
- Dosing to effect and adjust dosing as t1/2 decrease
Check BNF with any other drugs given
- Generalised Tonic - Clonic
Partial - All Not Absence Seizures
VGSC blockers 2: Phenytoin
- Pharmacology/mechanism of action:
- Pharmacokinetics:
- ADRs:
- DDIs
- How to monitor the drugs
- Epilepsy types treated with Phenytoin
- Phenytoin prolongs VGSC inactivation state
- Well absorbed – but 90% bound in plasma competitive binding can increases levels (see DDIs) Also CYP450 inducer (CYP3A4 - not CYP2C9 & CYP2C19 which metabolise Phenytoin)
Sub-therapeutic concs linear PK but NON-LINEAR PK at therapeutic concns - very variable t 1/2 = 6-24hrs
- Very wide ranging Type A’s: CNS – dizziness ataxia headache nystagmus nervousness
Gingival Hyperplasia (20%)
Rashes - Hypersensitivity + Stevens Johnson (2-5%)
- Competitive binding eg with Valproate (AED) NSAIDs/ salicylate increases plasma levels- exacerbates Non-Linear PKs
Very wide range of interactions including Oral Contraceptives decrease
Cimetidine - Phenytoin increase
Must check BNF for any other drugs given in combination
- Drug Monitoring
Close monitoring of free concn plasma
Can use salivary levels as indicator of free plasma
- Generalised Tonic-Clonic
Partial - All Not
Absence Seizures
Plots from five patients showing highly non linear PKs and variability in dose necessary to get to therapeutic levels.
VGSC blockers 3: Lamotrigine
- Pharmacology:
- Pharmacokinetics:
- ADRs
- DDIs
- Epilepsy types treated with LTG
- Lamotrigine (LTG) prolongs VGSC inactivation state Ca2+ channel blocker ? Glu release decrease ?
- Well absorbed – Linear PK t1/2= 24hrs (Phase II)
No CYP450 induction -> fewer DDIs
- Less marked CNS Dizziness ataxia somnolence Nausea. Still some mild (10%) and serious (0.5%) skin rashes
- Adjunct therapy with other AEDs.
Oral Contraceptives reduce LTG plasma level
Valproate increase LTG in plasma (competitive binding)
- Partial Seizures
Generalised - Tonic-clonic and Absence Seizures and other subtypes
LTG increasingly first line AED for Epilepsy
Not first line paediatric use as ADRs increase
Appears safer in pregnancy ?
Enhancing GABA Mediated Inhibition
- Fucntion?
- Distinct pharmacological targets I
Binding with GABAA receptor
Direct GABA agonists e.g.
- Major role in post synaptic inhibition – 40% synapses in brain are GABA-ergic
GABA (Increase) is natural anticonvulsant or excitatory ‘brake’ - Benzodiazepine Site – Enhance GABA action
Barbiturate Site – Enhance GABA action
General Mechanism for GABA Mediated Inhibition Enhancement
- Increased Chloride current into neurone - increases threshold for action potential generation
- Reduces likelihood of epileptic neuronal hyper – activity
Makes memb. potential more negative
Enhancing GABA Mediated Inhibition
Distinct pharmacological targets II GABA Metabolism
Which target sites enhance action of GABA
Inhibition of GABA inactivation ( GABA inc)
Inhibition of GABA re-uptake (GABA inc)
Increase rate of GABA synthesis (GABA inc)
Enhancing GABA Mediated Inhibition 1
Valproate
- Pharmacology:
2. Pharmacokinetics:
- ADRs
- DDIs
- How would we monitor the drug
- Epilepsy types treated with Valproate
- Evidence in vitro for mixed sites of action - pleiotropic
Weak Inhibition of GABA inactivation enzymes - GABA increase
Weak Stimulus of GABA synthesising enzymes - GABA increase
VGSC blocker + Weak Ca2+ channel blocker - Discharge decrease
- Absorbed 100% - then 90% plasma bound
Linear PK t 1/2 = 15 hrs
- Generally less severe than with other AEDs
CNS sedation ataxia tremor - weight gain
Hepatic function Transaminases increase in 40% patients
Rarely - hepatic failure
- Adjunct therapy with other AEDs –
Care needed with adjunct therapy. Both Valproate and adjunct PKs affected. Always check BNF.
Antidepressants - SSRIs MAOIs TCAs & TCA inhibit action of Valproate
Antipsychotics - antagonise Valproate by lowering convulsive threshold.
Aspirin - competitive binding in plasma Valproate increase
- Close monitoring of free concn plasma
Can use salivary levels as indicator of free plasma
Plasma Valproate not closely associated with efficacy
Monitor for blood, metabolic and hepatic disorder.
- Partial Seizures
Generalised: Tonic-clonic + Absence Seizures
Enhancing GABA Mediated Inhibition 2
Benzodiazepines
- Pharmacology:
- Pharmacokinetics:
- ADRs
- DDIs
- Epilepsy types treated with BZDs
Side effects limit first line use
- Benzodiazepines (BZDs) act at distinct receptor site on GABA Chloride channel (see earlier slide)
Binding of GABA or BZD enhance each others binding
Act as positive allosteric effectors
Increases Chloride current into neurone - increases threshold for action potential generation
- Well absorbed 90-100% highly plasma bound 85-100% Linear PK t 1/2 vary 5-45hrs
- Sedation
Tolerance with chronic use
Confusion impaired co-ordination
Agression
Dependence/Withdrawal with chronic use
Abrupt withdrawal seizure trigger
Respiratory and CNS Depression
- Some adjunctive use
Overdose reversed by IV flumazenil but its use may precipitate seizure/arrhythmia.
- Lorazepam / Diazepam – Status Epilepeticus
Clonazepam – Absence seizure short term use
AEDs and Pregnancy
- Balance of Risk
- Epilepsy vs AED Teratogenicity
- If Mild disease you may decide?
- Severe disease/ Status Epilepticus you may decide?
Need to consider each patient individually and stage of pregnancy
- Stop treatment
- Harm to both mother and baby if treatment is stopped? Severe fits prolonged hypoxia bad for mother and baby
- What are the three effects AED have on pregnancy?
Failure of Contraception
Failure rate x 4 with Carbamazepine/Phenytoin increase to between = 4-8%
Dangers to foetus during Pregnancy
- Congenital malformations ( All AEDs ?)
- Valproate - neural tube defects
- Facial and digit hypoplasia
Following birth
• Learning difficulties / mild neurological dysfunction?
AED risk of birth defects =?% vs =2% normally
8
AEDs and Pregnancy
- Solution of severe or status epilepticus?
- Treatment best avoided and why?
- Treat best used and why
- With multiple AED Teratogenic Risk increase, use single AED agent if possible at lowest dose
- Valproate best avoided - neural tube defect increase
- Lamotrigine may be safest - birth defect rate = 2 %
Valproate and Pregnancy – 2017
- Recent studies highlighting risks of Valproate
- Revised estimates of birth defect = 10%
- Neurodevelopmental disorders - e.g.? risk may be as high as 30-40%
- 1 in 5 pregnant women on valproate unaware of risk meaning?
learning/autism
Risks known for 40 yrs – doctor/patient communication issue