Classify anti epileptics
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I now have comprehensive data from Adams & Victor's Principles of Neurology to deliver a thorough classification. Let me compile the full answer:
Classification of Antiepileptic Drugs (AEDs)
AEDs are classified in several complementary ways: by generation, by mechanism of action, by seizure type indication, and by clinical use (monotherapy vs. adjunctive).
1. Classification by Generation
First-Generation AEDs
Introduced before the 1990s. Have narrow therapeutic windows, complicated pharmacokinetics, significant drug-drug interactions, and mostly hepatic metabolism.
| Drug | Key Feature |
|---|---|
| Phenytoin | Non-linear pharmacokinetics; enzyme inducer |
| Carbamazepine | Enzyme inducer; risk of hyponatremia |
| Phenobarbital | Enzyme inducer; sedating |
| Primidone | Metabolized to phenobarbital |
| Valproic acid | Enzyme inhibitor; teratogenic; weight gain |
| Ethosuximide | Narrow indication (absence seizures) |
| Benzodiazepines (diazepam, clonazepam, lorazepam) | Tolerance and sedation |
Second-Generation AEDs
Introduced 1990s-2000s. More predictable pharmacokinetics, fewer drug interactions, improved tolerability.
| Drug | Key Feature |
|---|---|
| Lamotrigine | Enzyme inducer; risk of Stevens-Johnson syndrome |
| Levetiracetam | SV2A modulator; mood/psychiatric side effects |
| Topiramate | Multiple mechanisms; cognitive impairment, weight loss |
| Gabapentin | Adjunctive only; renally cleared |
| Pregabalin | Adjunctive only; weight gain |
| Oxcarbazepine | Hyponatremia; enzyme inducer |
| Vigabatrin | Retinal toxicity (visual field loss) |
| Zonisamide | Nephrolithiasis; weight loss |
| Tiagabine | Adjunctive only |
| Felbamate | Reserved (aplastic anemia, hepatotoxicity) |
Third-Generation AEDs
Newer agents with refined mechanisms and improved tolerability profiles.
| Drug | Key Feature |
|---|---|
| Lacosamide | Slow Na+ channel inactivation; also IV formulation |
| Brivaracetam | Higher SV2A affinity than levetiracetam; less psychiatric side effects |
| Eslicarbazepine | Active metabolite of oxcarbazepine |
| Perampanel | Selective AMPA receptor antagonist |
| Cenobamate | Na+ channel + GABA modulation; newer |
| Cannabidiol (Epidiolex) | For Dravet/Lennox-Gastaut syndromes |
2. Classification by Mechanism of Action
A. Sodium Channel Blockers (inhibit rapid, repetitive firing)
- Phenytoin
- Carbamazepine
- Oxcarbazepine
- Eslicarbazepine
- Lamotrigine
- Lacosamide (slow/sustained inactivation - unique)
- Zonisamide
- Topiramate (partial)
- Rufinamide
B. GABA Potentiators (enhance inhibitory neurotransmission)
- GABA-A receptor agonists: Phenobarbital, Primidone, Benzodiazepines (diazepam, lorazepam, clonazepam, clobazam)
- GABA reuptake inhibitors: Tiagabine
- GABA transaminase inhibitors: Vigabatrin (irreversible)
- Topiramate (partial), Valproic acid (partial)
C. Calcium Channel Blockers
- T-type Ca²+ blockers: Ethosuximide, Valproic acid, Zonisamide
- N/P/Q-type (α2δ subunit): Gabapentin, Pregabalin
D. Glutamate/Excitatory Amino Acid Antagonists
- AMPA receptor antagonists: Perampanel
- NMDA antagonists: Valproic acid (partial), Felbamate (partial)
- Topiramate (AMPA inhibition, partial)
E. Synaptic Vesicle Protein 2A (SV2A) Modulators
(Modulate synaptic vesicle release of neurotransmitters)
- Levetiracetam
- Brivaracetam (higher affinity)
F. Multiple / Broad Mechanisms
| Drug | Mechanisms |
|---|---|
| Valproic acid | Na+ channel, T-Ca²+ channel, GABA potentiation, NMDA inhibition |
| Topiramate | Na+ channel, GABA-A potentiation, AMPA inhibition, Ca²+ channel |
| Zonisamide | Na+ channel, T-Ca²+ channel, dopaminergic effects |
3. Classification by Seizure Type Indication
Focal (Partial) Seizures
- Carbamazepine, Oxcarbazepine (first-line)
- Phenytoin, Lamotrigine, Levetiracetam, Lacosamide
- Gabapentin, Pregabalin (adjunctive)
- Eslicarbazepine, Brivaracetam (adjunctive)
Generalized Tonic-Clonic Seizures
- Valproic acid (first-line)
- Levetiracetam, Lamotrigine, Topiramate
- Phenobarbital, Phenytoin
Absence Seizures
- Ethosuximide (first-line - T-type Ca²+ blocker)
- Valproic acid (especially if mixed seizure types)
- Lamotrigine
- Avoid: Carbamazepine, Phenytoin (may worsen absence)
Myoclonic Seizures
- Valproic acid (first-line)
- Levetiracetam, Clonazepam, Topiramate, Zonisamide
- Avoid: Carbamazepine (worsens myoclonus)
Infantile Spasms (West Syndrome)
- Vigabatrin (especially tuberous sclerosis)
- ACTH/corticosteroids
Lennox-Gastaut Syndrome
- Valproic acid, Lamotrigine, Topiramate
- Rufinamide, Cannabidiol (Epidiolex)
- Felbamate (last resort)
Status Epilepticus (Acute)
- IV Lorazepam or Diazepam (first-line)
- IV Phenytoin / Fosphenytoin (second-line)
- IV Levetiracetam, IV Lacosamide, IV Valproate
- IV Phenobarbital
4. Monotherapy vs. Adjunctive-Only Agents
| Category | Drugs |
|---|---|
| Monotherapy approved | Valproic acid, Phenytoin, Carbamazepine, Oxcarbazepine, Lamotrigine, Levetiracetam, Topiramate, Phenobarbital, Ethosuximide, Lacosamide |
| Adjunctive use only | Gabapentin, Pregabalin, Vigabatrin, Clonazepam, Diazepam, Perampanel, Tiagabine, Eslicarbazepine, Brivaracetam |
5. Quick-Reference Summary Table
| Drug | Generation | Mechanism | Main Seizure Use | Key Adverse Effect |
|---|---|---|---|---|
| Phenytoin | 1st | Na+ block | Focal, GTC | Gingival hyperplasia, hirsutism, enzyme inducer |
| Carbamazepine | 1st | Na+ block | Focal, GTC | Hyponatremia, SJS (HLA-B*1502) |
| Valproic acid | 1st | Multiple | All types | Teratogenicity, hepatotoxicity, weight gain |
| Phenobarbital | 1st | GABA-A | Focal, GTC | Sedation, cognitive impairment |
| Ethosuximide | 1st | T-Ca²+ | Absence only | GI upset, hiccups |
| Lamotrigine | 2nd | Na+ block | Focal, generalized | SJS/TEN, requires slow titration |
| Levetiracetam | 2nd | SV2A | Focal, generalized | Irritability, mood changes, psychosis |
| Topiramate | 2nd | Multiple | Focal, generalized | Cognitive dulling, nephrolithiasis |
| Gabapentin | 2nd | α2δ Ca²+ | Focal (adjunctive) | Somnolence, weight gain |
| Vigabatrin | 2nd | GABA-T block | Infantile spasms | Irreversible visual field loss |
| Oxcarbazepine | 2nd | Na+ block | Focal | Hyponatremia |
| Lacosamide | 3rd | Slow Na+ inact. | Focal, GTC | PR interval prolongation |
| Perampanel | 3rd | AMPA block | Focal, generalized (adj.) | Aggression, dizziness |
| Brivaracetam | 3rd | SV2A | Focal, generalized | Better tolerated than levetiracetam |
| Eslicarbazepine | 3rd | Na+ block | Focal (adj.) | Hyponatremia |
Sources:
- Adams and Victor's Principles of Neurology, 12th Ed., Table 15-5 - Antiepileptic Drugs-General Principles
- Brenner and Rector's The Kidney - First- and Second-Generation Antiepileptic Drugs (renal dosing context)
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