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Which antiepileptic does not act via sodium channel blockade? (DNB Dec 2011)
Ans. A Vigabatrin
Vigabatrin (γ vinyl GABA. - is all inhibitor of GABA-transaminase, hence ↓es breakdown of GABA and ↑es it's concentration in synaptic cleft.
- Useful in refractory epilepsy especially partial seizures with/ without generalization
- S/E: Behavior changes, depression, psychosis.
- Carbamazepine: Prolongation of sodium channel inactivation
- Lamotrigine: Prolongation of sodium channel inactivation; in addition it may directly block voltage sensitive Na+ channels.
- S/E: Sleepiness, dizziness, diplopia, ataxia, Rash. Phenytoin: Prolongation of sodium channel inactivation.
- Gabapentin: Lipophilic GABA derivative which crosses to the brain and enhances GABA release, but doesnot act as agonist at GABA receptor.
- It is now the first line drug for pain due to diabetic neuropathy and post herpetic neuralgia.
- Topiramate: Weak carbonic anhydrase inhibitor; has broad-spectrum anticonvulsant activity.
- Also have other mechanisms of action like prolongation of Na+ channel inactivation, GABA potentiation by a post-synaptic effect and antagonism of certain glutamate receptors.
- S/E - Sedation, ataxia, Weight loss (weight gain by valproate), renal stones.
Tiagabine - Inhibits GABA transporter