How anti-seizure medications work
Anti-seizure medications (ASMs), formerly called antiepileptic drugs (AEDs), reduce the tendency of brain nerve cells to generate or propagate excessive electrical discharges. Different ASMs work through distinct mechanisms: some enhance inhibitory neurotransmission (GABAergic mechanisms), others reduce excitatory neurotransmission (blocking sodium or calcium channels), and some modulate multiple pathways. The choice of ASM is guided primarily by seizure type rather than a one-size-fits-all approach.
Approximately 60–70% of people with epilepsy achieve seizure freedom with appropriate ASM monotherapy. The remaining 30–40% may require combination therapy or are considered drug-resistant. Early identification of drug-resistant epilepsy (failure of two appropriately chosen and tolerated ASMs) is important because it prompts referral for further evaluation including potential surgical candidacy assessment rather than continued medication cycling.
Related: Epilepsy Doctor → · Dr. Jitendra Knowledge Hub → · ICHD-3 Topic →
Common medications by seizure type
Generalised tonic-clonic seizures respond well to lamotrigine, levetiracetam, valproate (in men and post-menopausal women), topiramate and zonisamide. Focal (partial) seizures respond to lamotrigine, levetiracetam, carbamazepine, oxcarbazepine, valproate, topiramate and lacosamide. Absence seizures respond to ethosuximide (first-line), valproate and lamotrigine. Myoclonic seizures respond to valproate and levetiracetam; carbamazepine, oxcarbazepine and vigabatrin may worsen myoclonus and should be avoided.
Special populations require tailored selection: women of childbearing age benefit from lamotrigine and levetiracetam (lower teratogenic risk); valproate is associated with higher teratogenic risk and is generally avoided in this group unless alternatives are ineffective. Elderly patients tolerate lamotrigine, levetiracetam and lacosamide well. Patients with renal impairment require dose adjustment for renally excreted agents (levetiracetam, gabapentin, pregabalin). Drug interactions must be reviewed — enzyme-inducing ASMs (carbamazepine, phenytoin, phenobarbital) reduce efficacy of oral contraceptives and other medications.
- Lamotrigine — broad-spectrum, well-tolerated, low teratogenic risk
- Levetiracetam — broad-spectrum, few drug interactions, weight-neutral
- Valproate — highly effective but teratogenic, avoid in women of childbearing age
- Carbamazepine/oxcarbazepine — effective for focal seizures, enzyme-inducing
- Topiramate — broad-spectrum, may cause cognitive side effects and weight loss
- Lacosamide — focal seizures, well-tolerated, minimal interactions
Medication review and monitoring
Regular medication review ensures optimal dosing, identifies side effects early, and assesses ongoing need for therapy. Blood tests may be required for ASMs with haematological or hepatic toxicity potential (valproate, carbamazepine, phenytoin). Therapeutic drug monitoring (TDM) is useful for phenytoin, carbamazepine and valproate to ensure levels are within the therapeutic range. ASMs with broad therapeutic windows (levetiracetam, lamotrigine, lacosamide) generally do not require routine TDM.
Side effects range from sedation and dizziness (dose-dependent, often transient) to long-term concerns including weight changes, bone health (enzyme-inducing ASMs reduce vitamin D), mood changes (particularly levetiracetam-related irritability in some patients), and teratogenicity. Adherence is the most common cause of breakthrough seizures — simplifying regimens (once-daily dosing when possible), addressing side effects proactively, and involving patients in medication decisions sustain long-term compliance. Dr. Jitendra Prasad Yadav (NMC 8029) provides comprehensive medication review at Kathmandu Neurology Clinic & Cognitive Center, Durbar Marg, Opposite of Yak & Yeti Hotel.