Phenytoin prevents seizures by blocking which channels from recovering from the inactivated state?

• A. Calcium Channels
• B. Potassium Channels
• C. Sodium Channels
• D. Chloride Channels

Answer: (C)

Phenytoin works by stabilizing voltage-gated sodium channels in their inactivated state and slowing their recovery back to the resting, ready-to-fire state. This selective, use-dependent binding means neurons have a longer refractory period during high-frequency firing, which dampens seizure activity. Since the drug targets the recovery of sodium channels from inactivation, the correct idea is that it blocks those channels from returning to the active state. Other channels aren’t the primary target here—calcium channels are involved in different seizure types and are targeted by other drugs, potassium channels are opened or modulated by different agents, and chloride channels relate to GABAergic inhibition rather than phenytoin’s action.