# Antiepileptic Drug Classes by Seizure Type

> Which antiepileptic drug is first-line for each seizure type?

Every antiseizure drug class by mechanism, the first-line pick for each seizure type and syndrome, the new ILAE 2025 terms, the status epilepticus clock and 2024 pregnancy guidance.

First-line antiseizure medication (the newer name for antiepileptic drugs) follows seizure type: ethosuximide for absence seizures; valproate for generalized tonic-clonic and myoclonic seizures, or levetiracetam when pregnancy is possible; lamotrigine, levetiracetam or carbamazepine for focal seizures; and a benzodiazepine for status epilepticus. Carbamazepine, oxcarbazepine, phenytoin and gabapentin can worsen absence and myoclonic seizures.

## Which antiepileptic drug is first-line for each seizure type?

Choose the drug in three passes. Classify the seizure as focal, generalized or unknown; name the syndrome, because childhood absence epilepsy, juvenile myoclonic epilepsy, infantile spasms, Lennox-Gastaut and Dravet syndrome each have preferred drugs, and most have drugs to avoid; then fit the patient, weighing pregnancy potential, contraception, HLA risk and interactions. Narrow-spectrum sodium-channel blockers control focal seizures but can aggravate absence and myoclonic ones, while broad-spectrum valproate, levetiracetam, lamotrigine and topiramate cover both, so they are the safer picks when a stem never says where a seizure began.

Guidelines now say antiseizure medication (ASM); question banks still say antiepileptic drug. About 60% of people with epilepsy have focal seizures, and the [Neurology](/topics/neurology) hub gathers the related guides.

## First-line drugs by seizure type and syndrome

Each row gives the stem clue, first choice, fallbacks and drugs that worsen that seizure type.

| Seizure type or syndrome | Stem clue | First-line | Alternatives or add-ons | Avoid |
| --- | --- | --- | --- | --- |
| Focal, including focal-to-bilateral tonic-clonic | Aura, Jacksonian march, lip smacking, Todd paralysis | Lamotrigine, levetiracetam, carbamazepine or oxcarbazepine | Topiramate, phenytoin; valproate second-line | Ethosuximide (absence only) |
| Generalized tonic-clonic | Tongue biting, incontinence, postictal confusion | Valproate; lamotrigine or levetiracetam if pregnancy is possible | Topiramate; perampanel add-on | Carbamazepine, phenytoin or gabapentin if absence or myoclonus coexists |
| Typical absence, childhood absence epilepsy | Age 5 to 15, stares of 10 to 30 seconds, hyperventilation trigger, 3 Hz spike-and-wave | Ethosuximide | Valproate (covers tonic-clonic too); lamotrigine | Carbamazepine, oxcarbazepine, phenytoin, phenobarbital, gabapentin, pregabalin, tiagabine, vigabatrin |
| Myoclonic, juvenile myoclonic epilepsy | Teen with morning jerks after sleep loss or alcohol, 4 to 6 Hz polyspike-and-wave | Valproate; levetiracetam if pregnancy is possible | Topiramate, zonisamide | Carbamazepine, oxcarbazepine, phenytoin, gabapentin, pregabalin, tiagabine, vigabatrin; lamotrigine may aggravate |
| Tonic or atonic | Sudden stiffening or drop attacks | Valproate; lamotrigine if pregnancy is possible | Lennox-Gastaut options | Carbamazepine, oxcarbazepine, gabapentin, pregabalin, tiagabine, vigabatrin |
| Infantile epileptic spasms syndrome, including West syndrome | Flexion spasm clusters in the first year, hypsarrhythmia | IM ACTH, oral corticosteroids or vigabatrin; vigabatrin in tuberous sclerosis complex | -- | -- |
| Lennox-Gastaut syndrome | Tonic seizures, drop attacks, atypical absences, intellectual disability, slow spike-and-wave under 2.5 Hz | Valproate | Clobazam, lamotrigine, rufinamide, topiramate, felbamate, cannabidiol, fenfluramine; ketogenic diet, vagus nerve stimulation, callosotomy | Drugs that worsen tonic or atonic seizures |
| Dravet syndrome | SCN1A variant, prolonged fever-triggered seizures from 6 to 12 months | Valproate, clobazam | Stiripentol, topiramate, fenfluramine, cannabidiol | Carbamazepine, oxcarbazepine, phenytoin, lamotrigine |
| Status epilepticus | Seizure over 5 minutes, or no recovery between seizures | IM midazolam, IV lorazepam or IV diazepam | Fosphenytoin, valproate or levetiracetam | -- |
| Eclampsia | Seizure with preeclampsia | Magnesium sulfate | Delivery | -- |
| Febrile seizure | Age 6 months to 5 years, fever above 38 °C | No daily drug | Benzodiazepine rescue at 5 minutes | Routine daily ASMs |
| Neonatal seizures | Newborn; correct glucose, calcium and magnesium | Phenobarbital | Levetiracetam, fosphenytoin | -- |

## ILAE 2025 seizure classification and the older names

The International League Against Epilepsy (ILAE) updated its seizure classification in Epilepsia in April 2025. Four classes remain (focal, generalized, unknown whether focal or generalized, and unclassified), but the 63 seizure types of 2017 shrink to 21. Consciousness, judged by awareness and responsiveness, replaces awareness as the classifier for focal and unknown seizures; observable versus non-observable manifestations replace motor versus nonmotor; the word onset leaves the class names; and epileptic negative myoclonus becomes a seizure type.

| ILAE 2025 term | 2017 ILAE term | Older name | Exam clue |
| --- | --- | --- | --- |
| Focal preserved consciousness seizure | Focal aware seizure | Simple partial seizure | Aura or Jacksonian march the patient remembers |
| Focal impaired consciousness seizure | Focal impaired awareness seizure | Complex partial seizure | Lip smacking or chewing automatisms, postictal confusion |
| Focal-to-bilateral tonic-clonic seizure | Focal to bilateral tonic-clonic seizure | Secondarily generalized seizure | Aura or one-sided start, then a convulsion |
| Generalized tonic-clonic seizure | Generalized onset motor, tonic-clonic | Grand mal seizure | Convulsion with tongue biting or incontinence |
| Typical absence seizure | Generalized onset nonmotor, absence | Petit mal seizure | Brief stare with 3 Hz spike-and-wave |
| Generalized epileptic spasms | Generalized onset motor, epileptic spasms | Infantile spasms | Flexion clusters in an infant |
| Unknown whether focal or generalized | Unknown onset | -- | Unwitnessed convulsion |

Generalized seizures now fall into three groups: absence seizures (typical, atypical, myoclonic absence, eyelid myoclonia), generalized tonic-clonic seizures, and other generalized seizures such as myoclonic, tonic, atonic and epileptic spasms. A focal-to-bilateral tonic-clonic seizure stays in the focal class, so an aura or a Todd paralysis (brief weakness opposite the focus) points to a focal-seizure drug however dramatic the convulsion. The cortical map in [stroke localization](/blog/stroke-localization-usmle) finds the focus, and this [seizure classification question](/blog/2026-06-12-q-bank-breakdown-seizure-classification-why-every-answer-choice-matters) drills the new terms.

## Antiepileptic drug classification by mechanism

Antiseizure drugs sort into about ten target classes, and the target predicts both spectrum and toxicity.

| Mechanism | Drugs | Main use | Signature toxicity or interaction |
| --- | --- | --- | --- |
| Sodium channels, use-dependent block | Phenytoin, fosphenytoin, carbamazepine, oxcarbazepine, lamotrigine, rufinamide; lacosamide (slow inactivation) | Focal seizures; lamotrigine is broad | HLA-B\*15:02 skin reactions; carbamazepine and phenytoin induce enzymes |
| T-type calcium channels, thalamic | Ethosuximide; zonisamide in part | Absence only (ethosuximide) | GI upset, blood dyscrasias |
| GABA-A, more frequent opening | Lorazepam, midazolam, diazepam, clobazam | Status epilepticus; clobazam in Lennox-Gastaut and Dravet | Sedation, respiratory depression |
| GABA-A, longer opening | Phenobarbital | Neonatal seizures; backup in status epilepticus | Enzyme induction; cardiac malformations; may aggravate absence |
| GABA breakdown or reuptake | Vigabatrin (GABA transaminase), tiagabine (GAT-1) | Vigabatrin for infantile spasms | Vigabatrin: permanent visual field loss; both may worsen absence |
| SV2A vesicle protein | Levetiracetam | Focal, tonic-clonic, myoclonic; status epilepticus | Irritability, aggression, psychosis; renal excretion |
| AMPA receptor, noncompetitive | Perampanel | Focal from age 4; tonic-clonic add-on from 12 | Boxed warning: aggression, homicidal ideation |
| Alpha2-delta calcium-channel subunit | Gabapentin, pregabalin | Focal add-on; postherpetic neuralgia | May worsen absence and myoclonus |
| Carbonic anhydrase plus several targets | Topiramate | Focal, tonic-clonic, Lennox-Gastaut; migraine prevention | Kidney stones, angle-closure glaucoma, non-anion gap acidosis, cognitive slowing |
| NMDA block plus GABA-A | Felbamate | Refractory focal seizures; Lennox-Gastaut | Boxed warning: aplastic anemia, liver failure |
| Several, GABA effects most likely | Valproate | Broadest spectrum | Boxed warning: liver failure, pancreatitis, fetal harm; raises lamotrigine levels |

## Why sodium-channel blockers fail absence seizures

Absence seizures arise in a thalamocortical circuit, and ethosuximide is thought to work by blocking T-type calcium channels there, which is why it is highly effective for absence and no other seizure type. Sodium-channel blockers act in a use-dependent way, suppressing high-frequency trains of cortical action potentials far more than single spikes; that suits a cortical focus but does not touch the thalamic generator, and carbamazepine, oxcarbazepine and phenytoin can even make absence and myoclonic seizures more frequent. Barbiturates may also aggravate absence, and gabapentin and pregabalin have no activity against it. Lamotrigine is the exception among sodium-channel blockers: an accepted option for typical absence that can still aggravate myoclonic seizures in juvenile myoclonic epilepsy.

## Diagnosis: EEG patterns and provoked seizures

EEG often names the syndrome: 3 Hz generalized spike-and-wave on a normal background in typical absence, 4 to 6 Hz polyspike-and-wave in juvenile myoclonic epilepsy, slow spike-and-wave under 2.5 Hz on a disorganized background in Lennox-Gastaut, and chaotic, high-voltage hypsarrhythmia in infantile spasms. Rule out a provoked seizure first. Low glucose, sodium, calcium or magnesium, alcohol or drug withdrawal, CNS infection and drug toxicity call for treating the cause rather than starting an ASM, and whether to treat after a single unprovoked seizure is debated and decided with the patient.

## Status epilepticus: the treatment clock

Status epilepticus is a convulsion lasting more than 5 minutes, or 2 or more seizures without full recovery of consciousness between them; older definitions used 30 minutes. The 2016 American Epilepsy Society guideline for prolonged seizures sets the clock.

| Phase (2016 AES guideline) | Time from onset | What to give |
| --- | --- | --- |
| Stabilization | 0 to 5 minutes | Airway, breathing, circulation; correct hypoglycemia and other reversible causes |
| Initial therapy | 5 to 20 minutes | One full dose of IM midazolam, IV lorazepam or IV diazepam; only lorazepam and diazepam are repeated |
| Second therapy | 20 to 40 minutes | Fosphenytoin, valproate or levetiracetam; IV phenobarbital if none is available |
| Third therapy | 40 to 60 minutes | Repeat a second-line drug, or anesthetic doses of midazolam, propofol, pentobarbital or thiopental with continuous EEG |

IM midazolam outperformed IV lorazepam in adults without IV access, so the first dose never waits for a line, and no second-line drug has proven superior; lacosamide is another option. Fosphenytoin is dosed in phenytoin sodium equivalents (PE), 15 to 20 mg PE/kg for status epilepticus, and its boxed warning caps infusion at 150 mg PE per minute in adults because faster rates cause severe hypotension and arrhythmias. Purple glove syndrome, linked to IV phenytoin, has also been reported after peripheral fosphenytoin. Rehearse the timing with this [status epilepticus question](/blog/2026-06-12-q-bank-breakdown-status-epilepticus-why-every-answer-choice-matters).

## Eclampsia and febrile seizures

Eclampsia is treated with magnesium sulfate, 4 g IV over 20 minutes and then 2 g per hour, and cured by delivery; a sudden loss of reflexes signals magnesium toxicity, treated with calcium gluconate 1 g IV. Simple febrile seizures, between 6 months and 5 years, last under 15 minutes without focal features or a repeat within 24 hours. About 20 to 35% recur, yet daily ASMs are usually not indicated and antipyretics do not prevent recurrence; a seizure lasting 5 minutes or more gets rectal diazepam or intranasal midazolam (see [febrile seizures for Step 1](/blog/2026-05-01-everything-you-need-to-know-about-febrile-seizures-for-step-1)).

## Pregnancy and contraception under the 2024 AAN guideline

The AAN, American Epilepsy Society and Society for Maternal-Fetal Medicine guideline, published in Neurology in May 2024, replaced the 2009 guidance and compares unadjusted major congenital malformation rates with single-drug therapy.

| Drug | 2024 AAN finding | Takeaway |
| --- | --- | --- |
| Lamotrigine | Major malformations 3.1%, among the lowest | Preferred; estrogen lowers its levels |
| Levetiracetam | Major malformations 3.5% | Preferred; few interactions |
| Oxcarbazepine | Major malformations 3.1% | Lower-risk option |
| Valproate | Highest major malformation rate, 9.7%; neural tube defects 1.4%; lower IQ at age 6 | Avoid in people with epilepsy of childbearing potential if clinically feasible |
| Topiramate | Oral clefts 1.4%, second only to phenobarbital; possibly more small-for-gestational-age births | Avoid if feasible to cut cleft risk |
| Phenobarbital | Highest cardiac malformation (4.4%) and oral cleft (2.2%) rates | Avoid when clinically feasible |

Prescribe at least 0.4 mg of folic acid daily before conception and through pregnancy, monitor ASM levels throughout pregnancy, and once a patient is pregnant, be cautious about removing or replacing an ASM that controls tonic-clonic seizures. Valproate's US label carries a boxed warning for fetal risk, says it should not treat epilepsy or bipolar disorder in women who are pregnant, planning pregnancy or of childbearing potential unless other drugs have failed or are unacceptable, and contraindicates it for migraine prevention in pregnancy or without effective contraception. In the UK, a woman or girl able to have children may receive valproate only within the Pregnancy Prevention Programme, and since January 2024 it should be started before age 55 only if two specialists agree that other treatments do not work and the benefits outweigh the risks.

Contraception interacts in both directions. Carbamazepine, phenytoin and phenobarbital lower hormone levels, topiramate weakens contraception mainly above 200 mg a day, perampanel 12 mg a day cuts levonorgestrel exposure by about 40%, and estrogen-containing pills lower lamotrigine levels by about 50%. The broader list is in [CYP450 inducers and inhibitors](/blog/2026-06-23-everything-you-need-to-know-about-cyp450-enzymes-inducers-inhibitors-for-step-1).

## Toxicities and interactions that decide questions

Signature toxicities come from a handful of drug labels and two HLA alleles.

- **HLA-B\*15:02:** the FDA advises avoiding carbamazepine in carriers unless benefit outweighs risk, and its pharmacogenetic table also flags severe skin reactions with oxcarbazepine, phenytoin, fosphenytoin and lamotrigine; HLA-A\*31:01 adds carbamazepine skin risk in Japanese, Korean and European ancestry.
- **Phenytoin:** metabolism saturates, so a small dose increase can cause a large jump in level; the range is 10 to 20 mcg/mL, with nystagmus near 20 and ataxia near 30. Gingival hyperplasia, coarse facies, cerebellar atrophy and fetal hydantoin syndrome complete the list.
- **Carbamazepine:** boxed warnings for serious skin reactions and for aplastic anemia and agranulocytosis, plus euvolemic hyponatremia and autoinduction; it lowers warfarin and contraceptive levels.
- **Lamotrigine:** boxed rash warning, about 0.3 to 0.8% of patients aged 2 to 17 and 0.08 to 0.3% of adults, nearly always within 2 to 8 weeks. The October 2025 label names valproate, fast titration and HLA-B\*15:02 as boxed risk factors, and valproate slows lamotrigine glucuronidation, roughly halving the dose needed.
- **Valproate:** fatal liver failure is likeliest under age 2 on several ASMs and in POLG mitochondrial disease, a contraindication; hyperammonemia can occur with normal liver tests.
- **Felbamate, vigabatrin, topiramate:** aplastic anemia possibly over 100 times background; permanent field loss in 30% or more, so vision is checked at baseline and every 3 months; kidney stones in 1.5% of adults.
- **Class warning:** pooled trials found about one extra case of suicidal thinking or behavior per 530 treated patients.

Cross-class look-alikes, such as other causes of Stevens-Johnson syndrome, are compared in [high-yield drug side effects](/blog/high-yield-drug-side-effects-usmle).

> **10-second drug picker:** stares with 3 Hz spike-and-wave -> ethosuximide. Morning myoclonus in a teen -> valproate, or levetiracetam if pregnancy is possible. Aura, automatisms or a march -> lamotrigine, levetiracetam or carbamazepine. Seizing past 5 minutes -> benzodiazepine, then fosphenytoin, valproate or levetiracetam. Could become pregnant -> avoid valproate, plus folic acid. Eclampsia -> magnesium sulfate.

## How USMLE tests antiseizure drugs

Most stems hide the seizure type in one detail, then ask for a drug, a mechanism or an adverse effect.

- **Flexion spasm clusters, hypsarrhythmia and tuberous sclerosis:** vigabatrin, with visual field checks.
- **Breakthrough seizures after a combined pill is added to lamotrigine:** estrogen halves lamotrigine levels.
- **Ataxia after a small phenytoin dose increase:** saturable, zero-order kinetics.

## Worked vignette: juvenile myoclonic epilepsy

A 15-year-old girl is brought to the clinic after a generalized tonic-clonic seizure at a sleepover where she stayed up most of the night. For several months she has had brief jerks of both arms within an hour of waking, often spilling her drink at breakfast. Examination is normal, and EEG shows generalized 4 to 6 Hz polyspike-and-wave discharges. She is sexually active and uses no contraception. Which long-term medication is most appropriate?

- A. Carbamazepine
- B. Ethosuximide
- C. Levetiracetam
- D. Phenytoin
- E. Valproate

**Answer: C, levetiracetam.** Morning myoclonus in an adolescent, a convulsion after sleep loss and 4 to 6 Hz polyspike-and-wave define juvenile myoclonic epilepsy. Valproate (E) is the classic first-line drug, and UK NICE still prefers it for boys and men, but the 2024 AAN, AES and SMFM guideline says clinicians must avoid valproate in people with epilepsy of childbearing potential when clinically feasible. NICE makes levetiracetam first-line for myoclonic seizures in women and girls able to have children, and it has an FDA indication as add-on therapy for myoclonic seizures in juvenile myoclonic epilepsy from age 12. Carbamazepine (A) and phenytoin (D) can worsen myoclonic seizures, and ethosuximide (B) treats absence only. She also needs at least 0.4 mg of folic acid daily and contraception counseling.

## Common wrong-answer traps

- **Carbamazepine or phenytoin for a generalized epilepsy.** Both can aggravate absence and myoclonic seizures.
- **Ethosuximide alone when tonic-clonic seizures coexist.** Used alone in mixed epilepsy it may increase them; valproate covers both.
- **Switching an effective drug after a positive pregnancy test.** The AAN advises caution in replacing an ASM that controls tonic-clonic seizures.

## Sources

- ILAE: [Updated classification of epileptic seizures (2025)](https://www.ilae.org/updated-classification-epileptic-seizures-2025), [position paper (PDF)](https://www.ilae.org/files/dmfile/updated-classification-of-epileptic-seizures-2025.pdf), [2017 seizure type checklist](https://www.ilae.org/guidelines/definition-and-classification/operational-classification-2017/ilae-2017-classification-of-seizure-types-checklist), [epilepsy syndromes (2022)](https://www.ilae.org/guidelines/definition-and-classification/classification-and-definition-of-epilepsy-syndromes)
- AAN, AES and SMFM: [In utero antiseizure medication exposure guideline (2024)](https://www.aan.com/Guidelines/Home/GuidelineDetail/1103), [clinician summary (PDF)](https://www.aan.com/Guidelines/Home/GetGuidelineContent/1104)
- NINDS: [epilepsy and seizures](https://www.ninds.nih.gov/health-information/disorders/epilepsy-and-seizures), [Lennox-Gastaut syndrome](https://www.ninds.nih.gov/health-information/disorders/lennox-gastaut-syndrome), [Dravet syndrome](https://www.ninds.nih.gov/health-information/disorders/dravet-syndrome), [infantile spasms](https://www.ninds.nih.gov/health-information/disorders/infantile-spasms), [febrile seizures](https://www.ninds.nih.gov/health-information/disorders/febrile-seizures)
- StatPearls (NCBI Bookshelf): [carbamazepine](https://www.ncbi.nlm.nih.gov/books/NBK482455/)

Lock in every seizure type, target and toxicity before test day: [Practice neurology pharmacology on StepGenie](https://dashboard.stepgenie.app/sign-up).

## Frequently asked questions

### How are antiepileptic drugs classified by mechanism?

Antiepileptic drugs, now called antiseizure medications, are grouped by molecular target. Phenytoin, carbamazepine, oxcarbazepine, lamotrigine and lacosamide act on sodium channels; ethosuximide blocks thalamic T-type calcium channels; benzodiazepines, phenobarbital, vigabatrin and tiagabine boost GABA signaling; levetiracetam binds the vesicle protein SV2A; perampanel blocks AMPA receptors; gabapentin and pregabalin bind the alpha2-delta calcium-channel subunit; and valproate, topiramate and felbamate act on several targets. The target predicts both spectrum and toxicity.

### Which drugs treat absence seizures?

Ethosuximide is the first-line drug for typical absence seizures, including childhood absence epilepsy, and valproate is the usual next choice. Valproate is preferred when generalized tonic-clonic seizures also occur, because ethosuximide treats absence alone, and lamotrigine is another option. Carbamazepine, oxcarbazepine, phenytoin, phenobarbital, gabapentin, pregabalin, tiagabine and vigabatrin can make absence seizures worse, so they are wrong answers when a stem describes brief staring spells with 3 Hz spike-and-wave.

### What is the treatment algorithm for status epilepticus?

Status epilepticus is a convulsion lasting more than 5 minutes or repeated seizures without recovery of consciousness between them. Under the 2016 American Epilepsy Society guideline, give a benzodiazepine between 5 and 20 minutes: IM midazolam, IV lorazepam or IV diazepam. If seizures continue at 20 to 40 minutes, give fosphenytoin, valproate or levetiracetam, none proven superior. Seizures persisting after 40 minutes call for a repeat second-line drug or anesthetic doses of midazolam, propofol, pentobarbital or thiopental with continuous EEG monitoring.

### Which antiseizure medications are safest in pregnancy?

In the 2024 AAN, American Epilepsy Society and Society for Maternal-Fetal Medicine guideline, lamotrigine, levetiracetam and oxcarbazepine had the lowest major malformation rates in monotherapy, 3.1% to 3.5%. Valproate had the highest, 9.7%, with neural tube defects and lower childhood IQ, so clinicians must avoid it in people with epilepsy of childbearing potential when clinically feasible. Phenobarbital had the highest cardiac and oral cleft rates, and topiramate also raised cleft risk. Patients should take at least 0.4 mg of folic acid daily, and drug levels are monitored through pregnancy.

### What changed in the ILAE 2025 seizure classification?

The International League Against Epilepsy published its updated seizure classification in April 2025. It keeps four classes, focal, generalized, unknown whether focal or generalized, and unclassified, but reduces 63 seizure types to 21. Consciousness, judged by awareness and responsiveness, replaces awareness, so focal aware seizures become focal preserved consciousness seizures and focal impaired awareness seizures become focal impaired consciousness seizures. Observable versus non-observable manifestations replace motor versus nonmotor, and epileptic negative myoclonus is now a seizure type.

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