Pharmacological Mx of epilepsy Flashcards
Epilepsy definition
Chronic neurological condition characterised by recurrent, unprovoked seizures
Types of epilepsy (onset) - two
- Focal - particular area in the brain from which seizure originate (e.g. hypocampus sclerosis due to meningitis, injury)
- Generalised - in all the areas of the brain
- unknown onset
What’s symptomatic vs idiopathic epilepsy?
Symptomatic - arise from an identifiable brain lesion
*usually focal that +/- generalise
Idiopathic - when an identifiable cause or structural lesion cannot be found (normal EEG, normal brain scan)
*usually generalised
*80-90% will achieve complete freedom from seizures
What’s the disadvantage of Phenobarbital? Do we prescribe it in the UK?
Phenobarbital is highly sedating -> we therefore do not prescribe it in the UK
* it is one of the oldest anti-epileptics
* it is one of the cheapest as well - some countries in the world still prescribe them a lot
Main MoA of anti-epileptic drugs (easy explanation - two types)
Remember: anti-epileptics either affect electrical current or neurotransmitter release (or both)
What do anti-epileptics do in terms of neuronal excitability and how do they do that?
Detailed: Reduce neuronal excitability
( Na+ and Ca++ channels)
Aim: to decrease depolarisation-induced Ca++ influx and vesicular release of neurotransmitters
What happens to Na+ channel at resting state? (in neuronal membranes)
They are closed -> ions are outside
What ions do get out of the cell and which ones go in?
Na+ go in
K+ go out
What do most anti-epileptic drugs do to the sodium channel?
They keep the Na+ gate closed (by increasing the rate of inactivation gate) -> so less Na+ ions will get into the cell
Simply: sodium channel blocker -> they reset electro-chemical gradient -> so to stop electrical impulse from starting one after another (across the neurones)
Just have a look at the pictures - MoA of anti-epileptic drugs
Some will inhibit passing on the action potential at different points at the pre-synaptic/ synaptic and post-synaptic
What is the general MoA of the drugs that are alternatives to usual anti-epileptics?
- usual anti-epileptics -> will reduce Glutamate (so reduce excitation of the neurones)
- alternatives -> will increase GABA -> so increase inhibition
What is MoA of GABA inhibitors?
They are allosteric modulators (increase) of GABAa receptor -> via the increasing frequency of Cl- channel opening -> prevents depolarisation -> less electrical firing
Benzodiazepines properties (6):
- sedatives
- anxiolytics
- muscle relaxants
- hypnotics
- anti- convulsant
- amnesic (e.g. Midazolam)
Phenytoin use (3)
Phenytoin
- Acute control of tonic-clonic seizures
- Rx of status epilepticus
- Prevention of seizures following neurosurgery or brain injury
Steps in acute Rx of status epilepticus
rectal diazepam/ IV lorazepam -> Phenytoin -> general anaesthetic
MoA of Phenytoin
Phenytoin
MoA: induces hyperpolarisation via sodium channels (blocks inactive Na+ channels) -> stabilises membranes -> prevents spread of seizure activity