Which antiepileptic does not act via sodium channel blockade?
A. Vigabatrin
B. Carbamazepine
C. Lamotrigine
D. Phenytoin
Ans. A.
Vigabatrin (y vinyl GABA) - is all inhibitor of GABA
- transaminase, hence decreases breakdown of GABA and increases its
concentration in synaptic cleft.
• Useful in refractory epilepsy esp 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 has 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, Wt
loss(wt gain by vaiproate), renal stones.
Tiagabine - Inhibits GABA transporter GAT - (which removes synaptically
released GABA into neurons and glial cells.)
