A seizure is a burst of abnormal, synchronized neuronal firing. Antiseizure medications (ASMs) stop seizures from starting or spreading by reducing excitation or increasing inhibition.

Broad- vs narrow-spectrum

• Broad-spectrum (focal and generalized seizures): valproate, levetiracetam, lamotrigine, topiramate, zonisamide, clobazam.
• Narrow-spectrum (focal seizures): carbamazepine, oxcarbazepine, phenytoin, lacosamide, gabapentin. Sodium-channel drugs such as carbamazepine and phenytoin can worsen absence and myoclonic seizures.
• Absence seizures: ethosuximide or valproate (lamotrigine alternative).

Indications: epilepsy (focal and generalized), status epilepticus, seizure prophylaxis after brain injury or surgery (short-term), and non-seizure uses (bipolar disorder — valproate, lamotrigine, carbamazepine; neuropathic pain — carbamazepine for trigeminal neuralgia, gabapentinoids; migraine prevention — topiramate, valproate).

Status epilepticus — time-based treatment (seizure ≥ 5 minutes or repeated seizures without recovery)

Class effects (most ASMs): dizziness, drowsiness, ataxia, diplopia, cognitive slowing; suicidal thoughts and behavior (FDA class warning); serious skin reactions (aromatic ASMs — phenytoin, carbamazepine, oxcarbazepine, lamotrigine, phenobarbital); DRESS (drug reaction with eosinophilia and systemic symptoms — fever, rash, swollen nodes, organ injury).

• Pregnancy: plan before conception; folic acid daily for everyone who can become pregnant. Valproate has the highest risk (neural tube defects, lower IQ, autism) — avoid in people who can become pregnant unless no alternative works, with effective contraception and a documented risk discussion; contraindicated in pregnancy for migraine prevention. Phenytoin, carbamazepine, phenobarbital, and topiramate (cleft lip) also raise risk. Lamotrigine and levetiracetam have the lowest known risk. Levels of lamotrigine and levetiracetam fall during pregnancy — monitor and adjust. Do not stop ASMs on discovering pregnancy without medical advice.
• Hormonal contraception: enzyme inducers (carbamazepine, phenytoin, phenobarbital, oxcarbazepine, topiramate at higher doses) reduce effectiveness — use an IUD or other reliable method. Estrogen-containing contraceptives lower lamotrigine levels.
• HLA-B*15:02: screen before starting carbamazepine in clients of at-risk Asian ancestry. The same allele raises SJS/TEN risk with phenytoin/fosphenytoin and oxcarbazepine — avoid them as substitutes in positive clients.
• Carbamazepine: contraindicated with MAO inhibitors and bone marrow depression; grapefruit raises levels.
• Valproate: contraindicated in liver disease, urea cycle disorders, and POLG mitochondrial disorders.
• Key interactions:
  • Valproate doubles lamotrigine levels — lamotrigine dose must be reduced
  • Carbapenem antibiotics (meropenem, ertapenem) sharply lower valproate levels → breakthrough seizures
  • Phenytoin, carbamazepine, and phenobarbital induce enzymes → lower warfarin, oral contraceptives, corticosteroids, many antiretrovirals, and other ASMs
  • Phenytoin is highly protein-bound: low albumin raises the free (active) drug — use a free level or corrected value
  • Enteral tube feedings reduce phenytoin absorption — follow agency protocol for holding feeds around doses
  • CNS depressants (alcohol, opioids, benzodiazepines) → additive sedation
• Older adults and kidney disease: reduce levetiracetam, gabapentin, and pregabalin doses by creatinine clearance.

Listed in priority order.

1. During IV loading (status epilepticus)
   • Airway, breathing, SpO₂; bag-valve mask and suction ready after benzodiazepines (respiratory depression, hypotension).
   • IV phenytoin: mix only with normal saline (precipitates in dextrose), use an in-line filter, give no faster than 50 mg/min (25 mg/min in older adults or cardiac disease; US boxed warning: cardiovascular risk with rapid infusion, also for fosphenytoin), continuous ECG and blood pressure, large vein, flush with saline before and after; check the site often for extravasation.
   • Fosphenytoin: up to 150 mg PE/min; still monitor ECG and BP; perioral tingling and itching are common.
2. Seizure precautions and observation — bed low, oxygen and suction at the bedside; time and describe any seizure.
3. Drug levels (trough, before the morning dose)
   • Phenytoin 10–20 mcg/mL (40–80 µmol/L); free phenytoin about 1–2 mcg/mL (4–8 µmol/L)
   • Carbamazepine 4–12 mcg/mL (17–51 µmol/L)
   • Valproate 50–100 mcg/mL (350–700 µmol/L)
   • Phenobarbital about 15–40 mcg/mL (65–170 µmol/L)
   • Check when starting, after dose changes, with new interacting drugs, pregnancy, loss of control, or suspected toxicity.
4. Laboratory safety monitoring
   • Sodium (carbamazepine, oxcarbazepine) — normal 135–145 mEq/L (135–145 mmol/L)
   • CBC (carbamazepine, valproate — platelets; ethosuximide)
   • Liver tests (valproate, carbamazepine, phenytoin); ammonia if a client on valproate becomes lethargic or confused
   • Lipase/amylase for abdominal pain on valproate
5. Skin and systemic reactions — assess for rash, fever, mucosal sores, swollen lymph nodes; stop and report any rash with lamotrigine, carbamazepine, or phenytoin.
6. Mood — screen for depression, irritability, and suicidal thinking.
7. Never miss doses — give on time; when NPO, clarify an IV or alternative route. Do not stop abruptly.
8. Oral care with phenytoin (brushing, flossing, dental visits).

• Take ASMs every day at the same time; link doses to a daily routine; use pill organizers and alarms.
• Never stop or change the dose on your own — sudden withdrawal can cause status epilepticus. Report side effects instead.
• Do not switch between brands or generic manufacturers without telling the prescriber (levels can change).
• Report immediately: any rash, blisters, mouth sores, fever with swollen glands; yellow skin or dark urine; severe abdominal pain (valproate); easy bruising, sore throat, or fever (carbamazepine); mood changes or thoughts of self-harm; confusion or unusual sleepiness.
• Avoid alcohol; check with a pharmacist before any new drug, supplement, or herbal product (e.g., St John's wort, grapefruit with carbamazepine).
• Pregnancy: plan pregnancy with the provider; take folic acid; use reliable contraception with enzyme-inducing drugs; do not stop medicines if pregnancy occurs — call the provider.
• Phenytoin: brush and floss daily, see a dentist regularly; take extra vitamin D and calcium if prescribed.
• Topiramate/zonisamide: drink plenty of fluids (kidney stones); children should avoid overheating.
• Wear medical identification; follow local driving laws; carry and teach family to use rescue medicine (intranasal or buccal midazolam, rectal diazepam) as prescribed; call emergency services for a seizure lasting 5 minutes or more.

• Status epilepticus = seizure ≥ 5 minutes → benzodiazepine first (IV lorazepam 0.1 mg/kg, max 4 mg; or IM midazolam), then fosphenytoin, valproate, or levetiracetam
• Phenytoin: 10–20 mcg/mL; normal saline only; ≤ 50 mg/min; gingival hyperplasia; nystagmus = early toxicity
• Fosphenytoin up to 150 mg PE/min
• Carbamazepine: hyponatremia, agranulocytosis, HLA-B*15:02 (SJS/TEN); 4–12 mcg/mL; HLA-B*15:02 also applies to phenytoin/fosphenytoin and oxcarbazepine
• Valproate: hepatotoxicity, pancreatitis, highest teratogenic risk; hyperammonemia → L-carnitine; carbapenems lower levels
• Lamotrigine: rash — slow titration; valproate doubles levels
• Levetiracetam: mood changes and irritability; few interactions
• Enzyme inducers reduce hormonal contraceptive and warfarin effects
• All ASMs: suicidal thoughts warning; never stop abruptly
• Folic acid for anyone who can become pregnant; lamotrigine and levetiracetam are preferred in pregnancy
• Carbamazepine and phenytoin can worsen absence seizures — ethosuximide or valproate for absence