Classify anti epileptic drugs
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Classification of Antiepileptic Drugs (AEDs)
AEDs are classified by generation (older vs. newer agents), mechanism of action, and seizure type/indication. All three frameworks are clinically useful.
1. Classification by Generation
Older (First-Generation) AEDs
| Drug | Trade Name |
|---|---|
| Phenytoin | Dilantin |
| Phenobarbital | Generic only |
| Primidone | Mysoline |
| Ethosuximide | Zarontin |
| Carbamazepine | Tegretol |
| Valproic acid / Divalproex | Depakote |
| Clonazepam | Klonopin |
| Diazepam | Valium |
Newer (Second/Third-Generation) AEDs
| Drug | Trade Name |
|---|---|
| Lamotrigine | Lamictal |
| Levetiracetam | Keppra |
| Topiramate | Topamax |
| Oxcarbazepine | Trileptal |
| Gabapentin | Neurontin |
| Pregabalin | Lyrica |
| Lacosamide | Vimpat |
| Zonisamide | Zonegran |
| Tiagabine | Gabitril |
| Felbamate | Felbatol |
| Vigabatrin | Sabril |
| Rufinamide | Banzel |
| Perampanel | Fycompa |
| Brivaracetam | Briviact |
| Eslicarbazepine acetate | Aptiom |
| Cenobamate | Xcopri |
| Clobazam | Onfi |
| Cannabidiol | Epidiolex |
| Fenfluramine | Fintepla |
| Stiripentol | Diacomit |
Newer agents have not been shown to be significantly more efficacious than older ones, but generally offer better pharmacokinetic profiles, fewer drug interactions, and improved tolerability. - Lippincott Illustrated Reviews: Pharmacology, p. 639
2. Classification by Mechanism of Action
A. Sodium Channel Blockers
Block voltage-gated Na+ channels - stabilize the inactive state, reduce repetitive neuronal firing.
| Drug | Notes |
|---|---|
| Phenytoin | Nonlinear (zero-order) kinetics; classic drug; causes gingival hyperplasia, nystagmus, ataxia |
| Fosphenytoin | Prodrug of phenytoin; preferred for IV/IM use |
| Carbamazepine | Also used for trigeminal neuralgia and bipolar disorder; induces own metabolism (autoinduction) |
| Oxcarbazepine | Prodrug (active metabolite = MHD); less enzyme induction than carbamazepine |
| Eslicarbazepine | Similar to oxcarbazepine; renal elimination |
| Lamotrigine | Also blocks HVA Ca2+ channels; broad-spectrum; risk of serious rash (Stevens-Johnson) if titrated too fast |
| Lacosamide | Enhances slow inactivation of Na+ channels; also binds CRMP-2 |
| Rufinamide | Na+ channel modulator; used in Lennox-Gastaut syndrome |
| Zonisamide | Dual Na+ + T-type Ca2+ blockade; sulfonamide derivative |
| Cenobamate | Na+ channel modulator + GABA-A allosteric modulator |
B. Calcium Channel Blockers (T-type)
Block T-type (low-voltage activated) Ca2+ channels - critical for thalamic pacemaker activity in absence seizures.
| Drug | Notes |
|---|---|
| Ethosuximide | Drug of choice for pure absence seizures only |
| Valproate | Also blocks Na+ channels and GABA-T; broadest spectrum AED |
| Zonisamide | Dual mechanism (also Na+ channel) |
C. GABA Enhancers
GABA-A Receptor Potentiators (increase Cl⁻ conductance)
| Drug | Notes |
|---|---|
| Phenobarbital | Increases duration of Cl⁻ channel opening; first-line for status epilepticus when benzodiazepines fail |
| Primidone | Metabolized to phenobarbital (major) and PEMA |
| Benzodiazepines (diazepam, lorazepam, clonazepam, clobazam) | Increase frequency of Cl⁻ channel opening; first-line for status epilepticus |
| Stiripentol | GABA-A modulator; used only with clobazam in Dravet syndrome |
| Cenobamate | PAM at GABA-A + Na+ blockade |
GABA Reuptake Inhibitors
| Drug | Notes |
|---|---|
| Tiagabine | Blocks GABA uptake into presynaptic neurons - more GABA available at synapse; adjunct for focal seizures only |
GABA Transaminase (GABA-T) Inhibitors
| Drug | Notes |
|---|---|
| Vigabatrin | Irreversible GABA-T inhibitor; increases synaptic GABA; causes visual field defects in >30% - requires REMS enrollment |
| Valproate | Also inhibits GABA-T |
D. Calcium Channel Blockers (HVA / α2δ Subunit)
Bind the α2δ subunit of voltage-gated Ca2+ channels - reduce excitatory neurotransmitter release.
| Drug | Notes |
|---|---|
| Gabapentin | GABA analog but does NOT act at GABA receptors; nonlinear kinetics; renal elimination; low interaction potential |
| Pregabalin | Same mechanism; linear kinetics; >90% renal elimination; also used for neuropathic pain, fibromyalgia |
E. Glutamate (Excitatory) Receptor Antagonists
| Drug | Receptor Target | Notes |
|---|---|---|
| Perampanel | AMPA receptor antagonist | Once-daily dosing (t½ ~105h); behavioral/psychiatric adverse effects |
| Topiramate | NMDA receptor + Na+ channels + Ca2+ channels + carbonic anhydrase | Multi-target; broad-spectrum; causes weight loss, kidney stones, cognitive slowing |
| Felbamate | NMDA receptor + Na+ channels + GABA-A modulation | Broad-spectrum but risk of aplastic anemia and hepatic failure limits use |
F. Synaptic Vesicle Protein (SV2A) Modulators
| Drug | Notes |
|---|---|
| Levetiracetam | Binds SV2A on synaptic vesicles - unique mechanism; broad-spectrum; minimal drug interactions; may cause irritability/behavioral changes |
| Brivaracetam | Higher affinity for SV2A than levetiracetam; fewer behavioral side effects |
G. Miscellaneous / Unique Mechanisms
| Drug | Mechanism | Notes |
|---|---|---|
| Cannabidiol | Unknown (not via CB1/CB2); modulates 5-HT1A, GPR55, TRPV1 | For Lennox-Gastaut, Dravet syndrome, tuberous sclerosis |
| Fenfluramine | 5-HT2 agonist | For Dravet syndrome; requires biannual echocardiogram for valvulopathy monitoring |
| Valproate | Multiple (Na+ block, GABA-T inhibition, T-Ca2+ block) | Broadest spectrum; hepatotoxic risk; teratogenic (spina bifida) |
3. Classification by Seizure Type (Therapeutic Indications)
| Seizure Type | First-Line Drugs |
|---|---|
| Focal (simple/complex partial) | Lamotrigine, Levetiracetam, Topiramate |
| Absence | Divalproex, Lamotrigine, Ethosuximide |
| Myoclonic | Divalproex, Levetiracetam |
| Tonic-clonic (generalized) | Lamotrigine, Levetiracetam, Topiramate |
| Status epilepticus | Benzodiazepines + Fosphenytoin / Levetiracetam / Valproate |
| Lennox-Gastaut syndrome | Cannabidiol, Divalproex, Lamotrigine, Topiramate |
| West syndrome (infantile spasms) | Corticotropin (ACTH), Vigabatrin |
| Dravet syndrome | Cannabidiol, Fenfluramine, Stiripentol + Clobazam |
| Benign rolandic epilepsy | Gabapentin, Lamotrigine |
Note: Carbamazepine is contraindicated in absence seizures - it may worsen them. - Lippincott Illustrated Reviews: Pharmacology, p. 643
4. Key Pharmacokinetic Highlights
| Drug | Special PK Feature |
|---|---|
| Phenytoin | Zero-order (saturable) kinetics - small dose changes cause disproportionate plasma level changes |
| Carbamazepine | Autoinduction of CYP enzymes - Cl increases over first few weeks |
| Gabapentin | Nonlinear absorption (saturable gut transporter) |
| Levetiracetam | Hydrolysis-based elimination; minimal hepatic metabolism |
| Perampanel | Extremely long t½ (~105 h) - once-daily dosing |
| Phenobarbital | Very long t½ (72-124 h) - slow accumulation |
| Valproate | Inhibits CYP2C9 and UGT - raises levels of lamotrigine, phenytoin, and others |
Quick Reference Summary
| Mechanism Class | Key Drugs |
|---|---|
| Na+ channel block | Phenytoin, Carbamazepine, Oxcarbazepine, Lamotrigine, Lacosamide |
| T-type Ca2+ block | Ethosuximide, Valproate |
| GABA-A potentiation | Benzodiazepines, Phenobarbital, Primidone |
| GABA reuptake inhibition | Tiagabine |
| GABA-T inhibition | Vigabatrin, Valproate |
| α2δ Ca2+ subunit binding | Gabapentin, Pregabalin |
| AMPA receptor antagonism | Perampanel |
| SV2A modulation | Levetiracetam, Brivaracetam |
| Multiple mechanisms | Topiramate, Valproate, Felbamate, Zonisamide |
| Unique/unknown | Cannabidiol, Fenfluramine, Stiripentol |
Source: Lippincott Illustrated Reviews: Pharmacology, Chapter 19 - Drugs for Epilepsy
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