Anti-Epileptic Drugs

Overview – Anti-Epileptic Drugs

Anti-epileptic drugs (AEDs), also known as anticonvulsants, are essential in the management of epilepsy—a condition marked by recurrent, unpredictable seizures. These drugs act via diverse mechanisms, targeting sodium, calcium, and GABA channels to reduce neuronal hyperexcitability and prevent seizure propagation. This page provides a detailed breakdown of anti-epileptic drugs, their mechanisms, and clinical considerations, including use in pregnancy.

Definition

Seizure

An episode of abnormal, synchronised, and rhythmic electrical discharge in the brain—effectively an “electrical storm.”

Epilepsy

A chronic neurological disorder marked by recurrent, unprovoked seizures (≥2 episodes), diagnosed via clinical history, EEG, and seizure observation. One seizure does not equate to epilepsy.

Seizures: Using the ICES System
Source: https://www.grepmed.com/images/3775/generalized-types-seizures-diagnosis-focal

Epidemiology

  • Prevalence: 0.5–1% of adults
  • Onset: Typically before age 20; many present before age 10
  • Causes: Often idiopathic but can be secondary to head trauma, toxins, or infections

Mechanisms of Seizure Development

  1. Altered Resting Membrane Potential
    → Brings neurons closer to threshold → spontaneous firing
  2. Ion Channelopathy
    → Mutated voltage-gated channels activate at lower thresholds
  3. Neurotransmitter Imbalance
    • ↑ Glutamate (Excitatory): Too much release or receptor activation
    • ↓ GABA (Inhibitory): Reduced synthesis, receptor function, or neuron density
    • Key receptors:
      • NMDA (Glutamate): Ca²⁺/Na⁺ channel → depolarisation
      • GABAA: Cl⁻ channel → hyperpolarisation
Neurons are Hyperexcitable
https://ppt-online.org/296144

Goals of Anti-Epileptic Treatment

  1. Suppress current seizures
  2. Prevent future seizures
  3. Avoid exacerbating underlying excitability
  4. Tailor therapy to individual seizure type and history

AED Use in Pregnancy

  • Risks: Most AEDs are teratogenic; Valproate and Phenytoin carry high risk
  • Defects: Spina bifida, cleft palate, microcephaly, congenital heart defects
  • Preferred Drug: Lamotrigine
  • Support: Folic acid supplementation reduces neural tube defects

Classification of Anti-Epileptic Drugs

Sodium Channel Blockers

Phenytoin

  • Indications: All except absence seizures; used with diazepam in status epilepticus
  • MOA: Prolongs Na⁺ channel recovery → inhibits rapid firing
  • Side Effects: Gum hyperplasia, hirsutism, vertigo, rash, teratogenicity, anaemia
Phenytoin
Phenytoin

Carbamazepine

  • Indications: 1st line for temporal lobe and most epilepsies (except absence)
  • Contraindications: Interacts with methylxanthines → risk of seizures
  • MOA: Prolongs Na⁺ channel recovery → inhibits rapid firing
  • Side Effects: Anti-diuretic effects, sedation, ataxia, blurred vision

Lamotrigine

  • Indications: General and partial seizures; safe in pregnancy
  • MOA: Na⁺ channel blocker + inhibits glutamate release
  • Side Effects: Dizziness, blurred vision, nausea, vomiting
Anti-epileptic drugs: Lamotrigine
(Note: The Above Diagram Applies to both Carbamazepine & Lamotrigine)
Image credit: Rang, Dale, et al. Pharmacology; available from: https://amzn.to/3Hr51dO

Calcium Channel Blockers

Ethosuximide

  • Indication: Absence seizures only
  • MOA: Inhibits T-type Ca²⁺ channels in thalamic neurons
  • Side Effects: Gum hypertrophy, nausea, headache, mood changes
  • Caution: Can aggravate tonic-clonic seizures
Anti-epileptic drugs: Ethosuximide
Image credit: Rang, Dale, et al. Pharmacology; available from: https://amzn.to/3Hr51dO

GABAA Receptor Modulators

Barbiturates (Phenobarbitone, Primidone)

  • Indications: Most seizure types except absence; not for adults due to abuse risk
  • MOA: Prolong GABA channel opening → ↑ Cl⁻ influx → hyperpolarisation
  • Side Effects: Sedation, intoxication-like sensation, vertigo, blood dyscrasias
Anti-epileptic drugs: Barbiturates
Image credit: Rang, Dale, et al. Pharmacology; available from: https://amzn.to/3Hr51dO

Benzodiazepines (Diazepam, Lorazepam, Clonazepam)

  • Indications: 1st line for status epilepticus; useful in myoclonic or absence seizures
  • MOA: Increase frequency of GABA channel opening
  • Side Effects: Sedation, dependence
GABA A Receptor
https://ppt-online.org/296144

Gabapentin

  • Indications: Partial and secondary generalised seizures
  • MOA: GABA analogue; unclear exact mechanism
  • Side Effects: Drowsiness, dizziness, ataxia
Anti-epileptic drugs: Gabapentin
(Benzodiazepines & Gabapentin Sites of action)
Image credit: Rang, Dale, et al. Pharmacology; available from: https://amzn.to/3Hr51dO

Multi-Mechanism AEDs

Valproate (Valproic Acid)

  • Indications: Broad-spectrum; effective for absence and generalised seizures
  • MOA:
    1. Na⁺ channel blockade
    2. Inhibits T-type Ca²⁺ channels
    3. ↑ GABA by enhancing synthesis and reducing breakdown
  • Contraindications: Strongly teratogenic → avoid in pregnancy
  • Side Effects: Baldness, weight gain, hepatotoxicity, GI symptoms, ataxia
Anti-epileptic drugs: Valproate
Image credit: Rang, Dale, et al. Pharmacology; available from: https://amzn.to/3Hr51dO

Non-Pharmacological Management

Ketogenic Diet

  • Macronutrients: High fat, low carb, moderate protein
  • MOA:
    • ↑ GABA via ketone metabolism
    • ↓ Glutamate availability
    • ↑ Na⁺/K⁺ ATPase activity → membrane stabilisation
  • Side Effects: Bloating, constipation (due to low fibre)

Summary – Anti-Epileptic Drugs

Anti-epileptic drugs reduce neuronal excitability and suppress seizure activity through diverse mechanisms including sodium, calcium, and GABA modulation. Choice of AED depends on seizure type, comorbidities, and patient factors such as pregnancy. Valproate, lamotrigine, phenytoin, ethosuximide, and benzodiazepines form the foundation of modern epilepsy management. For a broader context, see our Pharmacology & Toxicology Overview page.

Shopping Cart
Scroll to Top