Chapter 19  ·  Module 1
Seizure Classification & Drug Mechanisms
A visual summary of seizure types and anti-seizure drug categories
Seizure Classification
Focal Onset Begins in One Hemisphere
  • Without impaired awareness — conscious throughout
  • With impaired awareness — consciousness altered
  • Focal to bilateral tonic-clonic — spreads to both hemispheres
Generalized Onset Both Hemispheres from Start
  • Absence — brief staring, no postictal phase
  • Tonic-clonic — stiffening then rhythmic jerking
  • Myoclonic — sudden brief muscle jerks
  • Atonic — sudden loss of muscle tone
Figure 1 — Seizure Classification (Gemini)
Four Anti-Seizure Drug Mechanisms
Mechanism 1

Sodium Channel Blockade

Reduces high-frequency neuronal firing

  • Phenytoin
  • Carbamazepine
  • Lamotrigine
  • Lacosamide
Mechanism 2

Calcium Channel Blockade

Interrupts thalamic rhythm in absence seizures

  • Ethosuximide
  • Valproate (partial)
Mechanism 3

Gamma-Aminobutyric Acid Enhancement

Increases inhibitory chloride influx

  • Benzodiazepines
  • Phenobarbital
  • Valproate (partial)
Mechanism 4

Glutamate Inhibition

Reduces excitatory neurotransmission

  • Perampanel
  • Topiramate (partial)
  • Felbamate
Figure 2 — Four Mechanism Categories (Gemini)
High-Yield Syndromes
Childhood Absence Epilepsy
  • Drug of choice: ethosuximide (pure absence)
  • Valproate if other seizure types coexist
  • Carbamazepine, phenytoin, gabapentin worsen absence
Juvenile Myoclonic Epilepsy
  • Drug of choice: valproate
  • Covers myoclonic, tonic-clonic, and absence
  • Sodium channel blockers can worsen myoclonic seizures
Critical Rule — Drug Selection Follows Seizure Type
Using a narrow-spectrum agent (carbamazepine, phenytoin, gabapentin) in a patient with absence or myoclonic seizures can increase seizure frequency. Correct seizure classification before prescribing is a patient safety requirement.