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Antiseizure medications — choice and adverse effects
The choice of antiseizure medication is set by seizure type (focal or generalised), age and sex, and by each drug's signature adverse effects — and some focal drugs worsen absence and myoclonic seizures.
Why it matters in the exam
Many neurology questions ask "which drug fits" or "which adverse effect is expected": hyponatraemia with carbamazepine, a dangerous rash with lamotrigine, kidney stones with topiramate, gum hyperplasia with phenytoin, and visual field loss with vigabatrin. They also ask about the definition of epilepsy after a first seizure, interactions with the pill, and when a patient is drug-resistant and referred for surgical evaluation. A common distractor is carbamazepine for a child with absence seizures. By the practical definition, epilepsy is 2 unprovoked seizures more than 24 hours apart, or one seizure with a recurrence risk of 60 percent or more, or a defined epilepsy syndrome. After 2 years without seizures a gradual withdrawal can be considered, according to the epilepsy type and the EEG.
Key points
- Choose by seizure type: some focal drugs worsen absence and myoclonus.
- Valproate is broad-spectrum but teratogenic and hepatotoxic; lamotrigine needs slow titration because of rash.
- Carbamazepine and oxcarbazepine cause hyponatraemia and induce enzymes.
- After a first seizure, an EEG or MRI finding defines epilepsy and justifies treatment.
- Failure of 2 appropriate drugs defines resistance and requires referral for surgical evaluation.
Summary table
| Drug | Suited for | Main adverse effects |
|---|---|---|
| Valproate | Generalised seizures, including absence and myoclonus | Liver injury, pancreatitis, weight gain, tremor, hair loss, high teratogenicity, raised ammonia |
| Lamotrigine | Focal and generalised; relatively safe in pregnancy | Rash and Stevens-Johnson syndrome — needs slow titration; valproate doubles its level |
| Levetiracetam | Focal and generalised, broad spectrum, no major interactions | Irritability, depression and behavioural change |
| Carbamazepine and oxcarbazepine | Focal seizures; also trigeminal neuralgia | Hyponatraemia, enzyme induction, severe skin reaction in HLA-B*15:02 carriers; may worsen absence and myoclonus |
| Phenytoin | Focal seizures and status epilepticus | Gum hyperplasia, hirsutism, ataxia and nystagmus, saturable kinetics |
| Ethosuximide, topiramate, vigabatrin | Ethosuximide — absence only; vigabatrin — infantile spasms | Topiramate: kidney stones, weight loss, cognitive slowing, glaucoma; vigabatrin: visual field constriction |
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Sources
- NICE Guideline NG217: Epilepsies in Children, Young People and Adults, 2022 — Antiseizure medication by seizure type
- ILAE Official Report: A Practical Clinical Definition of Epilepsy, 2014 — Diagnosis after a single unprovoked seizure
- ILAE Definition of Drug Resistant Epilepsy, 2010 — Failure of two tolerated drug schedules
Sources are given for further reading; the text is written afresh and not copied from them.
Reviewed by the Examqo AI Professor · 2026-11-06. The text may contain errors; when in doubt, check the source.