Epilepsy: Management & Treatment

1. General Principles

• Serum drug levels guide initial dosing but are not the primary target — clinical response and tolerability are
• Free (unbound) drug levels are more relevant than total levels, especially in patients with hypoalbuminemia (hepatic or renal disease)
• Monitor for compliance, toxicity, and baseline levels before pregnancy

2. Antiseizure Drug Selection by Seizure Type

Focal (Partial) Seizures

Lamotrigine was significantly superior to carbamazepine, gabapentin, and topiramate for time-to-treatment failure in the SANAD trial (Marson et al., 2007). When rapid effect is needed, oxcarbazepine or levetiracetam are drugs of choice.

Generalized Seizures

Narrow-spectrum drugs (carbamazepine, phenytoin, gabapentin, pregabalin, tiagabine, oxcarbazepine) are appropriate only for focal seizures — do not use for generalized epilepsy.

Phenobarbital

3. Initiating & Adjusting Therapy

1. Start low, titrate slowly — wait ≥5 half-lives between dose increases (steady state)
2. If seizures persist at maximum tolerated dose → add a second drug, then taper the first
3. Switch drugs one at a time; never abruptly discontinue the first ASM
4. Polypharmacy: combining agents with different mechanisms of action is theoretically optimal; typical combinations: carbamazepine or lamotrigine + levetiracetam or valproate

4. When to Stop Therapy

• Seizure-free for 1–5 years
• Single seizure type (generalized better than focal)
• Normal neurological exam and intelligence
• No family history of epilepsy
• Normal EEG

5. Refractory Epilepsy (~30% of patients)

A. Further pharmacotherapy

• Rational polypharmacy with drugs of different mechanisms
• Add cenobamate, zonisamide, brivaracetam, topiramate, or lacosamide
• For refractory absence: valproate + ethosuximide combination
• For refractory myoclonic: add levetiracetam, zonisamide, or clonazepam

B. Epilepsy Surgery

• Resective surgery (most commonly anterior temporal lobectomy for mesial TLE): 80–90% seizure freedom in well-selected candidates
• Presurgical evaluation: video-EEG, high-resolution MRI, neuropsychological testing, and optionally ictal SPECT/PET

C. Vagus Nerve Stimulation (VNS)

• For patients who are not surgical candidates or fail surgery
• ~50% of patients achieve ≥50% reduction in seizure frequency

D. Deep Brain Stimulation (DBS)

• Anterior nucleus of thalamus (SANTE trial): 68% of patients had >50% seizure reduction at 5 years
• FDA-approved for drug-resistant epilepsy

E. Responsive Neurostimulation (RNS / NeuroPace)

• Detects ictal activity and delivers targeted stimulation
• ~48–70% seizure reduction in long-term follow-up; FDA-approved
• Particularly valuable for mesial temporal lobe epilepsy (70% median seizure reduction at 6 years)

F. Ketogenic Diet

• High-fat, low-carbohydrate diet; evidence-based especially in children
• Mechanism involves altered brain metabolism reducing seizure threshold

6. Status Epilepticus

• First-line: IV lorazepam (0.1 mg/kg, max 4 mg)
• Second-line: IV phenytoin / fosphenytoin or IV valproate or IV phenobarbital
• Urgent in nature — requires ICU management if refractory

7. Special Populations

• Avoid valproate if possible — significant teratogen (neural tube defects, cognitive effects)
• Prefer levetiracetam or lamotrigine
• Pregnancy registries document risks of individual ASMs

• Treatment generally not required
• Diazepam every 8 hours can be used for prophylaxis if carefully selected

Recent Evidence (PubMed 2024–2025)

• Li C et al. Int J Mol Sci 2025 — Reviews mechanisms of AED combinations and future strategies, highlighting that rational polypharmacy targeting different pathways (Na⁺ channels, GABA, AMPA, synaptic vesicle protein SV2A) improves outcomes (PMID 40362274)
• Auvin S. Rev Neurol 2025 — Targeted therapies in epilepsy: genetic testing now enables precision medicine (e.g., cannabidiol in Dravet syndrome, mTOR inhibitors in TSC, quinidine in KCNT1 mutations) (PMID 40221358)
• Perucca P et al. Epilepsia 2025 — Updated pregnancy registry data refining teratogenicity estimates by ASM exposure (PMID 39540312)

⚠️ The 2025 targeted therapy review (PMID 40221358) is notable: genetic/precision medicine is now an emerging treatment layer — genetic testing before drug selection is increasingly recommended, especially in children.

Epilepsy: Pathophysiology & Mechanisms

Core Concept: Failure of Excitation/Inhibition Balance

• Glutamate — principal excitatory neurotransmitter (acts at NMDA, AMPA, kainate receptors)
• GABA — principal inhibitory neurotransmitter (acts at GABA-A and GABA-B receptors)

1. Neuronal Mechanisms: The Depolarization Shift

• A large sustained membrane depolarization drives a burst of high-frequency action potentials
• Generated by a large excitatory synaptic current, amplified by voltage-gated intrinsic membrane currents (Na⁺, Ca²⁺, K⁺ channels)
• In physiological firing, Na⁺ channels open → action potential → spontaneous inactivation → refractory period → recovery
• In epileptic firing, high-frequency repetitive action potentials are sustained because channels rapidly recover from inactivation, bypassing the refractory brake
• Drugs like carbamazepine, phenytoin, and lamotrigine exploit this by prolonging Na⁺ channel inactivation, selectively suppressing high-frequency pathological firing without affecting normal slow firing

2. Synaptic Mechanisms

A. Reduced GABAergic Inhibition

• GABA-A receptor activation opens Cl⁻ channels → Cl⁻ influx → membrane hyperpolarization → ↓ neuronal excitability
• Reduced GABA synthesis, increased GABA catabolism, or GABA-A receptor dysfunction → disinhibition → seizure threshold falls
• Penicillin-induced seizures are a classic experimental model of GABA-A blockade
• Benzodiazepines and barbiturates both enhance GABA-A receptor-mediated Cl⁻ conductance (through distinct binding sites), which underlies their antiseizure efficacy

B. Enhanced Glutamatergic Excitation

• Excess activation at NMDA receptors (kainic acid model), AMPA receptors, or kainate receptors triggers seizures
• NMDA receptors allow Ca²⁺ influx, which further amplifies neuronal excitability and triggers downstream signaling cascades
• Abnormal Ca²⁺ homeostasis contributes to both acute seizure generation and chronic neuronal damage

C. Ion Channel Roles

3. Network Mechanisms: Synchronization & Spread

• In focal epilepsy, a localized seizure focus (irritative zone) initiates the discharge; surrounding tissue is initially inhibited (penumbra of hypometabolism)
• The seizure can remain focal or spread to adjacent and distant structures depending on the integrity of inhibitory networks
• In generalized epilepsy, the thalamo-cortical loop is central: rhythmic 3-Hz spike-and-wave discharges of absence epilepsy arise from cortico-thalamic oscillations involving thalamic relay neurons and reticular nucleus GABAergic interneurons
• Loss of inhibitory interneuron function (e.g., parvalbumin-positive fast-spiking interneurons) is a particularly critical failure point — these cells normally provide powerful, fast inhibition to pyramidal neurons

4. Epileptogenesis: How a Normal Brain Becomes Epileptic

Kindling Model

• Repeated subthreshold electrical stimulations of limbic structures (e.g., amygdala) → progressive intensification of seizure response → eventually spontaneous seizures persisting for life
• Demonstrates that repeated seizure activity itself modifies neural circuits — seizures beget seizures

Status Epilepticus → Hippocampal Sclerosis

• Prolonged seizures (status epilepticus) cause hippocampal neuronal death (especially CA1 and CA3 pyramidal cells, hilar interneurons)
• This mirrors the clinical observation that complicated febrile seizures in young children precede the development of mesial temporal lobe epilepsy years later
• The latent period between the initial insult and the onset of spontaneous seizures involves extensive network reorganization

Mossy Fiber Sprouting

• Surviving dentate granule cells (DGCs) sprout new axons (mossy fibers) that form aberrant recurrent excitatory connections within the dentate gyrus
• This creates a positive feedback loop that amplifies excitability in the hippocampal circuit
• Normally, DGCs are relatively non-excitable ("sparse activation"), acting as a gate against seizure propagation from entorhinal cortex to hippocampus — mossy fiber sprouting breaks this gate

5. Genetic Mechanisms

6. Drug Mechanism Summary

Summary