Antiepileptics · Pharmacology

Which of the following describes the primary mechanism of action for Phenytoin in controlling focal and generalized tonic-clonic seizures?

  1. Enhancement of GABA-A receptor-mediated chloride conductance in cortical neurons
  2. Blockade of voltage-gated sodium channels in their inactivated state
  3. Inhibition of T-type calcium channels in the thalamus
  4. Antagonism of NMDA-type glutamate receptors
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Correct answer: Blockade of voltage-gated sodium channels in their inactivated state

Phenytoin limits the repetitive firing of action potentials by slowing the rate of recovery of voltage-activated sodium channels from inactivation. This use-dependent blockade prevents the spread of seizure activity without interfering with normal low-frequency neuronal activity.

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