PH2113 - Neurodegenerative Disease and Epilepsy 11 Flashcards
How is the dose of anti-epilepsy medication determined?
By half life
- usually twice daily at average doses, but needs to be three times a day if large doses
- usually once daily for
- phenobarbital
- lamotrigine
- phenytoin
Increase in children
- monitor frequently
- they grow!
- can grow out of epilepsy
Why are new anti-epileptic medications needed?
Available compounds do not treat the disease
- merely control symptoms
Current therapy fails 50% of those with complex partial seizures
- focal
Inadequate control for potentially fatal status epilepticus
- unremitting series of seizures
- long running seizure
- brain damage
No therapy to prevent epileptogenesis
- some head injury/febrile seizure sufferers will develop epilepsy
Few drugs for absence seizures
Limited range of drugs for paediatric use
Most epilepsy drugs fail through toxicity
- not efficacy
Serious complications with some highly effective drugs
- tolerance
- foetal malformations
Side effects induce patient non-compliance
What is the “ideal” Anti-epileptic drug?
Efficacious
- the seizure free concept
Safe
- minimal or no side effects
- wide therapeutic index
Good PK profile
- good oral absorptoin
- no food effect
- low binding to proteins
- low extent of hepatic metabolism to avoid drug-drug interactions
- long half life
- at least twice daily dosing
- no accumulation
What is the mechanism of anti-epileptic drugs?
Antiepileptic drugs inhibit the abnormal neuronal discharge in epilepsy but do not resolve the underlying cause
Decrease excitatory mechanisms
Inhibition of sodium channel function
Inhibition of calcium channel function
Increase inhibitor brain mechanisms
Enhancement of GABA action
- global inhibitory neurotransmitter
How does enhancement of GABA action help treat the symptoms of epilepsy?
GABA is the main inhibitory neurotransmitter in the brain
Several drugs enhance activation of GABA(A) receptor
- allosteric modification
- benzodiazepines
- barbiturates
Facilitates GABA-mediated opening of chloride channels
Increasing Cl- permeability hyperpolarises the cell as Cl- ions enter
- more negative relative to outside
- reducing excitability
How can GABA be enhanced to treat epilepsy?
Tiagabine inhibits GABA uptake into neurones/glia
Vigabatrin irreversible inhibits GABA transaminase
- enzyme responsible for inactivating GABA
How does inhibition of sodium channels help to treat epilepsy?
How does use-dependent blocking action of sodium channels help treat epilepsy?
Depolarisation of a neurone increases the proportion of sodium channels in the inactivated state
Drugs bind preferentially to the inactivated state of sodium channels, preventing them from returning to the resting state
- reduces number of sodium channels available to generate action potentials
Give examples of anti-epileptic drugs which inhibit sodium channels?
Phenytoin
Carbamazepine
Lamotrigine
Sodium valproate
How can inhibition of the calcium channel treat epilepsy?
Drugs effective in absence seizures block T-type calcium channel activity
- ethosuximide
- sodium valproate
- clonaezepam
T-type channel activity is important for the rhythmic discharge of thalamic neurones in absence seizures
Gabapentin and pregabalin act on L and P/Q type channels and reduces calcium entry into nerve terminals and hence release of neurotransmitters
How can inhibition of the AMPA receptor treat epilepsy?
Perampanel inhibits AMPA-induced increases in intracellular calcium
- selectively blocks AMPA receptor-mediated synaptic transmission
- reduces neuronal excitation
How can inhibition of SV2A treat epilepsy?
Unique class of anti-epileptic drugs
- levetiracetam
- multiple possible sites of action
- more side effects
- biviracetam
- more selective SV2A binding
Synaptic vesicle protein
- binding reduces release of glutamate
How does topiramate treat epilepsy?
Multiple mechanisms of action
- voltage-gated sodium channels
- high voltage-activated calcium channels
- GABA(A) receptors
- AMPA/kainate receptors
- carbonic anhydrase isoenzymes
