Describe the physiological basis for the mechanism of action of three commonly used anticonvulsant groups. Give an example of a drug for each mechanism of action.
The three main anticonvulsant mechanisms required were:
1. Sodium channel blockers. These promote the inactive state of voltage activated Na
channels. Sodium channels are unable to open for a period of time making the neuron
more refractory to action potential generation. Rapid repetitive firing is diminished and
spread of electrical activity to adjacent brain areas is suppressed.
Examples: phenytoin, carbamazepine, lamotrgine, Na valproate
2. Drugs that enhance GABA mediated synaptic inhibition. This increases the influx of
chloride ions into the cell and hyperpolarizes the neuron. 3 mechanisms:
a. Act on GABA receptor. Example: benzodiazepines, barbiturates
b. Inhibit GABA transporter and reduce neuronal GABA reuptake. Example: tiagabine.
c. Promote GABA release. Example: gabapentin.
3. Drugs that inhibit Calcium channels. Limit activation of voltage activated Ca channel
known as the T current. Example.: Na valproate
Other mechanisms of action with examples if described earned extra marks. These included
glutamate /NMDA receptor inhibition. Example: magnesium.
It is impossible to guess how much detail they wanted for "extra marks", but hopefully something like this would be enough:
Ion channel modulators:
reduce neuronal excitability by altering the resting membrane potential, stabilising the channels involved in the conduction of action potentials, or inhibiting the intracellular calcium flux which triggers excitatory neurotransmitter release.
|GABA potentiators: Increased inhibitory neurotransmission by either directly affecting the GABA ligand-gated chloride channel, decreasing the reuptake of GABA from the synapse, or decreasing the breakdown of GABA.||GABAA||
|GABA reuptake transporter||
|Presynaptic neurotransmitter release modulators: decrease the release of neurotransmitters||SV2A||
|Postsynaptic inhibitors of neurotransmission: decrease the effect of released neurotransmitter ligands on their receptors||AMPA||
|God only knows what effect||
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