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Antiepileptic Drugs: Mechanisms & Drug of Choice

15 Jun 2026 2 min read By admin

Epilepsy is uncontrolled neuronal firing, so every antiepileptic drug does one of four things: damp sodium channels, damp calcium channels, boost GABA, or cut glutamate. Learn the four mechanisms below and you can place any drug — and predict the seizure type it treats.

How antiepileptic drugs work Block Na⁺ channels Phenytoin, carbamazepine, lamotrigine, oxcarbazepine, valproate → focal & tonic-clonic seizures Block T-type Ca²⁺ channels Ethosuximide, valproate → absence seizures Enhance GABA inhibition Benzodiazepines, barbiturates, valproate, vigabatrin, tiagabine → broad use & status epilepticus Reduce glutamate / SV2A Levetiracetam (SV2A), perampanel, topiramate, lamotrigine → broad-spectrum add-ons All four converge on ↓ neuronal excitability → seizure control
The four mechanisms of antiepileptic action — and the seizure types each one suits.

Sodium-channel blockers

  • Phenytoin — zero-order kinetics (small dose rise → big level jump), gum hypertrophy, hirsutism, enzyme inducer.
  • Carbamazepine — drug of choice for focal seizures and trigeminal neuralgia; auto-induction, hyponatraemia, risk of SJS (check HLA-B*1502).
  • Lamotrigine — broad-spectrum, well tolerated; titrate slowly to avoid rash.

Valproate — the broad-spectrum workhorse

Acts on sodium and calcium channels and enhances GABA — effective across seizure types. But: highly teratogenic (neural tube defects) — avoid in women of childbearing potential; also weight gain, tremor, hepatotoxicity.

Calcium-channel blockers (absence seizures)

Ethosuximide blocks T-type calcium channels in the thalamus — drug of choice for absence seizures. Valproate is the alternative (and preferred if generalised tonic-clonic seizures coexist).

GABA enhancers

  • Benzodiazepines (lorazepam, diazepam) — first-line for status epilepticus.
  • Phenobarbitone — effective but sedating; still used where resources are limited.

Newer broad-spectrum agents

Levetiracetam (binds SV2A) is increasingly first-line — few interactions, but mood/irritability effects. Topiramate and perampanel are useful add-ons.

Drug of choice — quick reference

  • Focal seizures: carbamazepine / lamotrigine / levetiracetam.
  • Generalised tonic-clonic: valproate (lamotrigine/levetiracetam in women).
  • Absence: ethosuximide or valproate.
  • Status epilepticus: IV benzodiazepine → then phenytoin/levetiracetam.
Exam tip: two high-yield safety points win marks every time — valproate is teratogenic (avoid in women of childbearing age) and ethosuximide is the drug of choice for absence seizures. Tie every drug back to a mechanism on the diagram.

Four mechanisms, a handful of first-choice drugs, and two safety red-flags — that framework will carry you through almost any antiepileptic question.

Test yourself

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A quick check on this topic — tap an answer for instant feedback.

  1. Q1. Drug of choice for absence seizures:

  2. Q2. Which antiepileptic is the most strongly teratogenic?

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