Seizures & Anti-epiletics CA Flashcards
What is a seizure?
A paroxysmal event due to an abnormal hyper-synchronous discharge from a mass of CNS neurons.
What is epilepsy?
A disorder of the brain characterised by repeated seizures.
What indicates a lower risk of recurrence of seizure?
- Single seizure
- Normal EEG
- Normal brain scan
What indicates a higher risk of recurrence of seizure?
- Previous (undiagnosed) seizures
- Epileptiform (abnormal) EEG
- Abnormal brain scan
Causes of epilepsy
- congenital/hereditary
- brain injury, scarring or tumour
- infections: meningitis or encephalitis
- blood glucose alterations: chronic hypoglycemia
- metabolic disorders: adrenal insufficiency leading to hyponatremia
Investigations to be ordered for epilepsy
- Blood tests (Liver function, blood chemistry– electrolytes, glucose, calcium & magnesium)
- EEG
- Brain scan (CT/MRI)
(to determine risk of recurrent seizures)
Epilepsy/seizure classification
- Generalised seizure: grand mal/tonic, petit mal/absence, myoclonic, atonic
- Partial seizure: simple, complex
- Status epilepticus: severe form, medical emergency
Rationale for the use of anti-epileptics
- Decrease membrane excitability by altering Na+ and Ca2+ conductance during action potentials.
- Enhance effects of inhibitory GABA neurotransmitters.
What are some common drugs used in the treatment of seizures and epilepsy?
Phenytoin, Carbamazepine, Valproate, Diazepam
What is the MOA of phenytoin?
Reduces excitatory sodium signals by acting as a blockade of voltage-dependent Na+ channels
Note: Narrow therapeutic range (<40 no effect, >100 becomes toxic)
Which anti-epileptic drug should be given first-line for newly diagnosed partial and generalised tonic clonic seizures?
- Carbamazepine
- Phenytoin
- Sodium valproate
Which anti-epileptic drug should be given first-line for absence seizure?
ONLY sodium valproate
Important contraindication of Phenytoin
Teratogenic: leads to birth defects in fetus, contraindicated in pregnant women!
What is the MOA of carbamazepine
Similar to phenytoin:
Reduces excitatory sodium signals by acting as a blockade of voltage-dependent Na+ channels
Important considerations on the use of Carbamazepine
- Drug interactions: Hepatic enzyme (CYP450) inducer, lead to reduced efficacy of other drugs metabolised by these enzymes, hence dosage of other drugs needs to be increased
- Side effects: Aplastic anemia due to inability of bone marrow to produce all kinds of blood cells
What is the MOA of valproate?
- Acts as a blockade of voltage-dependent Na+ and Ca2+ channels hence decrease excitatory tone
- Inhibits GABA transaminase (which breaks down GABA), hence increase GABA, increase inhibitory tone