Anti-epileptics Flashcards
How do seizures occur?
Secondary to repetitive neuronal discharges in the CNS
What are the 2 main effects of anticonvulsants?
- Action on CNS Na+
- Potentiating the neurotransmitter GABA
How do anticonvulsants work on the CNS Na+ channels?
- Selectively inhibit inactive fast Na channels
- Stabilise presynaptic Na channels by inhibiting the release of excitatory neurotransmitters
Which anticonvulsants work on Na channels?
Phenytoin
Lamotrigine
How do anticonvulsants work on potentiating GABA?
1) Opening Cl- channels allowing influx into cell causing cell hyperpolaroization = cell less excitable
2) GABA agonist
3) Inhibition of GABA transaminase the enzyme that catalyses the breakdown of GABA
Which anticonvulsants work on GABA receptors?
Benzos
Barbituates
Baclofen
Valproate
What is Phenytoin used for?
- Generalised seizures
- Partial seizures
- Status
- Trigeminal neuralgia
- Class Ib anti-arrhythmias
What are the SE of Phenytoin?
- Narrow therapeutic window
- Hirsutism
- Gum hyperplasia
- Acne
- Coarse facies
- Peripheral neuropathy
- Megaloblastic anaemia
What are the pharmacodynamics of Phenytoin?
- 90% protein bound
- Enzyme inducer CYP450
- Liver metabolises to inactive metabolites
- Renally excreted
- Undergoes satiation kinetics
- 0 order kinetics replace 1st order kinetics at high drug conc
What seizures is Sodium Valproate used for?
- Partial
- Myoclonic
- Grand mal
- Petit mal
- Chronic pain
What is the mechanism of action for valproate?
- Stabilises inactive Na channels
- Increases GABA conc
What are the SE of valproate?
Nausea
Thrombocytopenia
Hair loss
Neural tube defects
Liver dysfunction
How does Gabapentin work as an anticonvulsant?
- Increases GABA synthesis in the brain
- Modulates voltaged gated Ca2+ channels
- Inhibits excitatory glutamate
- Increases 5HT (serotonin) levels
