USMLE Step 3 Drug MOA Practice Test 2025 – All-in-One Exam Prep

Question: 1 / 400

What is the mechanism of action of lamotrigine in treating epilepsy?

It enhances GABA receptor activity

It stabilizes neuronal membranes by inhibiting sodium channels

Lamotrigine primarily functions by stabilizing neuronal membranes through the inhibition of voltage-gated sodium channels. By blocking these channels, lamotrigine reduces the excessive release of excitatory neurotransmitters, which is crucial in preventing seizure activity. This sodium channel blockade helps dampen the rapid depolarization of neurons that can lead to seizures, making it effective as an anticonvulsant.

While other mechanisms such as enhancing GABA activity or blocking calcium influx could theoretically have anticonvulsant effects, they are not the primary actions of lamotrigine. The drug's efficacy in epilepsy comes primarily from its ability to impact sodium channel dynamics, stabilizing neuronal firing and preventing the hyperexcitability central to seizure formation.

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It increases calcium influx in neurons

It blocks potassium efflux in neurons

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