Seizures for Step 1: Types, Antiseizure Drugs & Status

Creator: Progress Note
Published: 2026-05-19
Keywords: seizure types treatment USMLE, seizures usmle, antiseizure drugs mechanisms, absence seizure ethosuximide, focal vs generalized seizure, phenytoin side effects, valproate teratogen, status epilepticus treatment, benzodiazepine vs barbiturate gaba, carbamazepine agranulocytosis

bolt The 60-second version

check_circleFocal seizures start in one hemisphere (often the temporal lobe) and may impair awareness; generalized seizures involve both hemispheres from the start.
check_circleAbsence seizures: children, brief staring spells with no postictal confusion, 3-Hz spike-and-wave EEG; ethosuximide (T-type calcium channel blocker) is first line.
check_circleAlways check glucose, sodium, and calcium; metabolic problems and alcohol withdrawal provoke seizures.
check_circlePhenytoin and carbamazepine block sodium channels and induce CYP450; valproate is broad spectrum but hepatotoxic and teratogenic (neural tube defects).
check_circleBenzodiazepines increase the frequency of GABA-A channel opening; barbiturates increase the duration.
check_circleStatus epilepticus (≥ 5 minutes of seizure activity): benzodiazepine first, then fosphenytoin, levetiracetam, or valproate, then anesthesia.

target What you'll be able to do · aligned to USMLE Step 1 · Nervous System

NEUROClassify focal and generalized seizures.
NEUROIdentify common causes of seizures by age.
PHARMMatch antiseizure drugs to mechanisms, uses, and adverse effects.
NEUROOutline stepwise treatment of status epilepticus.

How seizures are tested on Step 1

Classify the seizure, then pick the drug.

Staring spells. Brief spells without an aura or postictal confusion point to absence seizures.

Causes by age: children — genetic syndromes, infection, fever (febrile seizures); adults — trauma, alcohol withdrawal, tumors; older adults — stroke, tumors, dementia.
Todd paralysis: temporary weakness after a focal seizure; can mimic stroke.
Juvenile myoclonic epilepsy: morning myoclonic jerks in teenagers; valproate or levetiracetam.

Antiseizure drugs

Know each drug's mechanism and its signature adverse effect.

Drug	Mechanism	Uses	Key adverse effects
Ethosuximide	Blocks thalamic T-type Ca²⁺ channels	Absence seizures	GI upset, fatigue
Valproate	Na⁺ channel block, ↑ GABA	Broad spectrum; myoclonic; bipolar disorder	Hepatotoxicity, pancreatitis, neural tube defects, weight gain
Phenytoin	Na⁺ channel block	Focal and tonic-clonic seizures	Gingival hyperplasia, hirsutism, nystagmus, SJS, CYP induction, zero-order kinetics
Carbamazepine	Na⁺ channel block	Focal seizures, trigeminal neuralgia	Agranulocytosis, SIADH, SJS (HLA-B*1502), CYP induction
Lamotrigine	Na⁺ channel block	Focal and generalized seizures; bipolar depression	Stevens-Johnson syndrome (titrate slowly)
Levetiracetam	Binds SV2A, reducing neurotransmitter release	Focal and generalized seizures	Irritability, mood changes
Benzodiazepines	↑ GABA-A opening frequency	Status epilepticus, alcohol withdrawal	Sedation, respiratory depression
Phenobarbital	↑ GABA-A opening duration	Neonatal seizures	Sedation, CYP induction
Topiramate	Na⁺ block, ↑ GABA	Seizures, migraine prevention	Kidney stones, weight loss, slowed thinking

Gabapentin and pregabalin bind the α2δ subunit of calcium channels and are also used for neuropathic pain.

Status epilepticus

Treat in timed steps.

Status epilepticus. Seizure activity of 5 minutes or more, or repeated seizures without recovery between them.

Pregnancy and special situations

Drug choice matters beyond seizure control.

Pregnancy: valproate carries the highest risk of neural tube defects and lower IQ; lamotrigine and levetiracetam are preferred. Give folic acid.
Drug interactions: carbamazepine and phenytoin induce CYP450 and lower oral contraceptive and warfarin levels.
Eclampsia: seizures in preeclampsia are treated with magnesium sulfate.

Worked example

Match the seizure to the drug.

functions Worked example — daydreaming in class

A 7-year-old is reported to "daydream" many times a day for about 10 seconds, then resume activity without confusion. Hyperventilation in clinic triggers an episode, and EEG shows 3-Hz spike-and-wave discharges. What is the diagnosis, and what drug is preferred?

Brief staring spells with immediate recovery fit absence seizures.
Hyperventilation provocation and 3-Hz spike-and-wave confirm it.
Absence seizures arise from thalamocortical circuits using T-type calcium channels.
Ethosuximide blocks these channels and is first line for absence seizures alone.

Answer. Absence seizures; ethosuximide.

Next in the roadmap

Seizures

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Try it now

3 real questions on Seizures & Antiseizure Drugs

Straight from the Progress Note question bank, each with a cited explanation. No account needed.

A 34-year-old man with HIV (CD4 count 40 cells/microliter) presents with headache, confusion, and a focal seizure. MRI brain shows multiple ring-enhancing lesions with surrounding edema, predominantly at the corticomedullary junction and basal ganglia. A biopsy is shown below. Which statement about the pathophysiology of this presentation is correct?

Image for question 1 — Jensflorian, CC BY-SA 3.0 <https://creativecommons.org/licenses/by-sa/3.0>, via Wikimedia Commons

A 23-year-old man is brought to the emergency department after a witnessed generalized tonic-clonic seizure. He reports a several-month history of worsening headaches and subtle personality changes. MRI brain shows a ring-enhancing lesion in the temporal lobe with surrounding vasogenic edema. Biopsy demonstrates sheets of small round blue cells with perinuclear clearing and Olig2 positivity. Which diagnosis is most likely?

Image for question 2 — RadsWiki, CC BY-SA 3.0 <https://creativecommons.org/licenses/by-sa/3.0>, via Wikimedia Commons

A 28-year-old woman with a history of partial-onset seizures refractory to carbamazepine is started on a new antiepileptic agent. After several weeks, the following is seen on CT. She reports difficulty with word-finding and cognitive slowing. Serum bicarbonate is found to be 18 mEq/L. Which of the following best explains the mechanism responsible for her metabolic disturbance?

Image for question 3 — James Heilman, MD, CC BY-SA 3.0 <https://creativecommons.org/licenses/by-sa/3.0>, via Wikimedia Commons

Frequently asked questions

What is the first-line drug for absence seizures?expand_more

Ethosuximide, which blocks T-type calcium channels.

Which antiseizure drug causes gingival hyperplasia?expand_more

Phenytoin.

What is the first drug for status epilepticus?expand_more

A benzodiazepine, such as IV lorazepam or IM midazolam.

Which antiseizure drug is most teratogenic?expand_more

Valproate, which causes neural tube defects.

References & further reading

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