Antiepileptic Drugs for NEET PG: Drug of Choice by Seizure Type and Pregnancy

Antiepileptic drugs are easy to memorise as a list and hard to apply, because the right drug depends on seizure type, the patient's sex and age, and whether pregnancy is possible. This post organises the topic around those three decisions. It also flags where guidelines disagree, so you are not surprised when an older source gives a different first-line drug.

A note on terms: the ILAE now recommends "antiseizure medications" because these drugs suppress seizures rather than cure the underlying epilepsy (see Perucca and French, Epilepsia 2024). This post keeps "antiepileptic drugs" as the familiar exam term and uses both names.

Key Takeaways

• Match the drug to the seizure type first: ethosuximide for typical absence, lamotrigine or levetiracetam for focal seizures, and lamotrigine, levetiracetam or valproate for generalised-onset seizures.

• WHO 2023 advises against valproate in women and girls of childbearing potential, and prefers lamotrigine or levetiracetam. The older WHO 2012 advice listed carbamazepine, phenobarbital, phenytoin or valproate.

• Phenytoin, carbamazepine and phenobarbital are potent CYP450 inducers and lower oral contraceptive levels. Valproate inhibits lamotrigine clearance.

• In pregnancy, valproate carries the highest malformation, neural tube defect and neurodevelopmental risk. Give folic acid of at least 0.4 mg daily and monitor lamotrigine levels.

• Learn each drug's signature adverse effect as a pair: phenytoin with gingival hyperplasia, valproate with hepatotoxicity and teratogenicity, carbamazepine with HLA-linked skin reactions, vigabatrin with visual field defects.

Drug of Choice for Antiepileptic Drugs by Seizure Type

The first-line antiepileptic drug depends on whether the seizure is focal, generalised or an absence seizure. The table below combines the WHO 2023 recommendations with the MSD Manual for seizure types WHO does not split out.

Sources: WHO mhGAP evidence centre, MSD Manual, NICE NG217, and the infantile spasms guideline update.

Why the Drug of Choice Differs Between Guidelines

The drug of choice has changed over time, so an older source can disagree with a newer one. WHO 2012 listed carbamazepine, phenobarbital, phenytoin or valproate monotherapy for convulsive epilepsy, with phenobarbital preferred first where supply was assured, and carbamazepine for partial-onset seizures. That was a strong recommendation based on low-quality evidence.

WHO 2023 moved to lamotrigine or levetiracetam for focal seizures and added lamotrigine, levetiracetam or valproate for generalised seizures, again as a strong recommendation, this time with high certainty (WHO mhGAP). When a question stem or a book gives an older answer, work out which guideline era it follows rather than assuming one is simply wrong.

Drugs That Can Worsen Certain Seizures

Some antiepileptic drugs aggravate specific seizure types, which makes them wrong choices even though they are effective elsewhere. Per the MSD Manual:

• Carbamazepine should not be used for absence, myoclonic or atonic seizures, and it can worsen myoclonus, Dravet syndrome and juvenile myoclonic epilepsy.
• Oxcarbazepine and gabapentin can also exacerbate juvenile myoclonic epilepsy.
• Lamotrigine can aggravate myoclonic seizures in some patients with JME and worsens myoclonus in Dravet syndrome.

If a stem describes myoclonic jerks on waking in an adolescent, think JME and ask which sodium-channel blocker would make it worse.

Status Epilepticus: A Stepwise Drug Sequence

Status epilepticus is treated in time-ordered steps, as laid out in the AES guideline (Glauser et al., 2016).

1. Initial therapy (5 to 20 minutes): a benzodiazepine, either IM midazolam, IV lorazepam or IV diazepam.
2. Second therapy (20 to 40 minutes): fosphenytoin, valproic acid or levetiracetam. No clear evidence shows that one is better than the others, and IV phenobarbital is a reasonable alternative if none is available.
3. Third therapy (after 40 minutes): evidence is lacking. Options are repeating second-line therapy or anaesthetic doses of thiopental, midazolam, pentobarbital or propofol with continuous EEG monitoring.

Mechanisms of Action of Antiepileptic Drugs

Most antiepileptic drugs act on ion channels, and the mechanism often explains why a drug suits one seizure type. The groupings below follow Mechanisms of Action of Antiseizure Drugs and a 2025 review of antiseizure medication pharmacology.

Ethosuximide's thalamic T-type calcium action fits its narrow use in typical absence. Valproate's mechanism is less clear-cut, so learn it as a broad-spectrum drug with several proposed actions.

Key Adverse Effects of Antiepileptic Drugs

Each antiepileptic drug has a signature toxicity, and these pairings are the most portable part of the topic. The table draws on the MSD Manual and the 2025 pharmacogenetics review.

Pharmacogenetic and Metabolic Warnings

Three genetic or metabolic warnings link a drug to a patient background. Carbamazepine-related SJS/TEN is associated with HLA-B15:02 in Han Chinese, Thai and Malaysian populations, and with HLA-A31:01 in Japanese and European-descent populations (PMC12287013). The carbamazepine label on DailyMed describes an intermediate HLA-B*15:02 prevalence in South Asians, including Indians.

Valproate can cause hyperammonaemia in urea cycle disorders such as OTC deficiency, and liver failure in POLG-related syndromes. The Depakote label's hepatotoxicity warning says the risk is greatest in the first six months and in children under two years or those with mitochondrial disease (source: the Depakote label on DailyMed).

Enzyme Inducers, Inhibitors and Drug Interactions

Phenytoin, carbamazepine and phenobarbital are the potent CYP450 inducers in this group, and they lower the levels of oral contraceptives, anticoagulants, antiretrovirals and cytotoxic drugs. They also lower vitamin D, which raises osteoporosis risk (MSD Manual). Inducers speed up the metabolism of co-prescribed drugs, which is why their levels fall.

Sources: MSD Manual, PMC12287013 and the lamotrigine prescribing information.

A simple way to retain this: draw three columns (inducers, inhibitor, affected drugs) from memory and place phenytoin, carbamazepine and phenobarbital in the first, valproate in the second, and lamotrigine plus the contraceptive pill in the third. This is a study layout, not a published mnemonic.

Antiepileptic Drugs in Pregnancy

Valproate is the worst choice in pregnancy, and the safer options are lamotrigine, levetiracetam and, per the AAN/AES/SMFM guideline, oxcarbazepine. The 2024 guideline on in utero exposure advises avoiding valproic acid where clinically feasible because of malformations and poor neurodevelopmental outcomes (Pack et al., Neurology 2024). It also advises avoiding valproate or topiramate to reduce the risk of small-for-gestational-age infants. WHO advises against valproate in women and girls of childbearing potential, and the MSD Manual says it is not generally recommended in women of childbearing age.

Malformation Risk by Drug

The table shows selected values for major congenital malformations per 1,000 pregnancies with monotherapy exposure. The guideline notes that most comparisons are indirect and of low confidence, so read the figures as a ranking rather than exact risks.

Source: Pack et al., Neurology 2024.

In the guideline text, valproate carries a 9.7% malformation risk against 3.1% for lamotrigine. Neural tube defects per 1,000 with monotherapy, from highest to lowest:

• Valproate: 14.3
• Carbamazepine: 5.6
• Phenobarbital: 4.1
• Oxcarbazepine: 3.5
• Lamotrigine: 3.4
• Levetiracetam: 3.1
• Phenytoin: 2.0

Phenobarbital showed the highest cardiac and oral cleft prevalence. The guideline also reports a higher malformation prevalence at higher doses of valproate and phenobarbital, so the lowest effective dose matters.

Neurodevelopment After Fetal Exposure

Fetal valproate exposure is linked to lower IQ. Mean IQ was 93.9 with valproate against 105.8 with lamotrigine (moderate confidence). Autism spectrum disorder per 1,000 was 41.9 with valproate, 14.5 with lamotrigine and 11.3 with levetiracetam, though confidence was low for most of these estimates (Pack et al., 2024). Topiramate in the first trimester carries roughly a tenfold higher oral cleft risk (PMC12287013).

Folic Acid, Vitamin K and Drug Levels

Folic acid of at least 0.4 mg daily is advised before conception and during pregnancy. The 2024 guideline did not find that folic acid reduced major malformations, but offspring outcomes were better when it was taken before and during pregnancy, and the data do not support a more specific dose. One study linked doses of 1 mg or more to childhood cancer (hazard ratio 2.7), though evidence is limited. The 2009 AAN/AES parameter likewise said at least 0.4 mg before pregnancy "may be considered" (Harden et al., Neurology 2009).

Two other points come from the same 2009 parameter:

• Evidence was inadequate to show that prenatal vitamin K reduces newborn haemorrhage. Newborns still receive vitamin K at delivery, as all newborns do.
• Lamotrigine clearance rises in pregnancy, so levels fall. Monitoring of lamotrigine, carbamazepine and phenytoin levels should be considered.

Breastfeeding

Older AAN data (2009) suggest primidone and levetiracetam probably pass into breast milk in clinically important amounts, and gabapentin, lamotrigine and topiramate possibly do. Valproate, phenobarbital, phenytoin and carbamazepine probably do not pass in clinically important amounts. The clinical effect on infants is poorly studied.

Quick Recap: Decision Order and Signature Pairs

This recap restates facts from the sections above as a study aid. Work through the decision order first, then cover the right-hand column of the pairs table and recall it.

1. Name the seizure type: focal, generalised-onset, typical absence, myoclonic or infantile spasms.
2. Check sex and pregnancy potential: valproate is advised against in women and girls of childbearing potential (WHO 2023).
3. Screen for seizure types a drug can worsen, such as carbamazepine in absence, myoclonic or atonic seizures.
4. Screen for interactions: the three potent inducers lower contraceptive levels, and valproate raises lamotrigine levels.
5. Note the signature toxicity you must counsel on.

Common Mistakes With Antiepileptic Drugs

These slips come from mixing up sources or skipping a step in the reasoning:

• Giving one fixed "drug of choice" for all epilepsy. Seizure type, sex, age and pregnancy potential all change the answer.
• Quoting valproate as first-line for a woman of childbearing potential without noting the WHO 2023 advice against it.
• Using carbamazepine for absence or myoclonic seizures, where it can make them worse.
• Forgetting that enzyme inducers make hormonal contraception unreliable, while estrogen-containing contraceptives also lower lamotrigine levels.
• Mixing up the older WHO 2012 list with the WHO 2023 recommendations.

For practice on these distinctions, work through the CNS drugs practice questions and the wider pharmacology question set. For a similar side-effect-focused revision format, see antitubercular drugs for NEET PG.

Conclusion

Choose the antiepileptic drug in three steps: identify the seizure type, check sex and pregnancy potential, then screen for interactions and signature toxicities. Lamotrigine and levetiracetam are the safest all-round options in the current WHO guidance, valproate is the drug to avoid in women who could become pregnant, and the three potent enzyme inducers are the ones that undermine contraception. Rebuild the drug-of-choice and pregnancy tables from memory, then test yourself with timed practice questions.