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Epilepsy & Anti-Seizure Drugs - Complete Explanation in Simple Words

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PART 1: What is Epilepsy?

• Epilepsy affects about 0.5 to 1% of all people worldwide
• More than 40 different forms of epilepsy exist
• Current medicines can control seizures but they do NOT cure epilepsy - there is no cure yet

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PART 2: What is a Seizure?

• Strange movements (shaking, jerking)
• Strange sensations
• Loss of consciousness
• Confused or dazed behavior
• Sometimes nothing visible at all (just a brief blank stare)

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PART 3: What Causes Seizures?

Key point: If seizures are caused by a temporary problem (like fever or low sugar), fixing the cause stops the seizures. Only repeated unprovoked seizures = epilepsy.

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PART 4: Types (Classification) of Epileptic Seizures

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GROUP 1: Partial (Focal) Seizures

A. Simple Partial Seizures (Jacksonian Seizures)

• Only ONE side of the brain fires abnormally
• Affects one limb or muscle group - for example, just one arm twitching
• The person stays conscious - they are awake and aware
• Symptoms stay the same throughout the seizure
• EEG (brain scan) shows: abnormal discharge from a small group of neurons on the opposite (contralateral) side of the brain

B. Complex Partial Seizures (Temporal Lobe Epilepsy / Psychomotor Seizures)

• Still focal, but now consciousness is impaired or lost
• The person looks confused, dazed, or behaves strangely
• "Automatisms" occur - these are repetitive, automatic movements like lip-smacking, hand-wringing, picking at clothes - the person is not in control
• Wide variety of symptoms possible
• Also called psychomotor seizures because behavior is affected

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GROUP 2: Generalized Seizures

A. Generalized Tonic-Clonic Seizures (Grand Mal)

• All body muscles contract (stiffen) powerfully at once
• Breathing stops temporarily (breathing muscles also contract)
• Body goes rigid

• Muscles rapidly alternate between contracting and relaxing
• This causes rhythmic jerking movements
• May lose control of bowel and bladder

B. Absence Seizures (Petit Mal)

• Very brief loss of consciousness - just 5-10 seconds
• The person stops mid-sentence and stares blankly
• No falling down, no convulsions
• May have slight eyelid fluttering
• Can happen dozens of times per day
• Common in children (looks like daydreaming or lack of attention)
• Caused by: abnormal rhythmic firing in the thalamus (a relay center in the brain) through low-threshold calcium channels (T-type)
• EEG shows: a very characteristic 3-per-second spike-and-wave pattern

C. Atonic Seizures (Drop Attacks)

• Sudden loss of muscle tone - the head droops or the person falls to the ground
• May lose consciousness briefly
• Very dangerous because of fall injuries

D. Clonic Seizures

• Rhythmic jerking of all muscles
• Loss of consciousness
• Strong effects on the autonomic nervous system (heart rate, etc.)

E. Myoclonic Seizures

• Sudden, brief muscle jerk - like an electric shock
• Usually affects both arms or the whole body
• The person remains conscious

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PART 5: Status Epilepticus - A Medical Emergency

• The brain is starved of oxygen (hypoxia)
• Blood becomes acidic (acidemia)
• Very high body temperature (hyperpyrexia)
• The heart and circulation can collapse
• Kidneys can shut down

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PART 6: Goals of Treatment

1. Block repetitive neuronal firing - stop brain cells from firing too fast
2. Block synchronization - stop many cells from all firing together
3. Block spread - stop the seizure from spreading to other brain areas
4. Use the simplest possible drug regimen with minimum side effects
5. Monotherapy (one drug) is preferred when possible

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PART 7: How Drugs Work - Three Strategies

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PART 8: The Drugs - One by One

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1. Phenytoin (Dilantin)

• Oldest non-sedating antiseizure drug
• IV form is fosphenytoin (a prodrug - converted to phenytoin in the body)
• Mechanism: Blocks sodium (Na+) channels - prevents rapid repetitive firing of neurons. Also alters Ca2+ and K+ channels and neurotransmitter levels

• Ataxia (loss of balance/coordination)
• Nystagmus (uncontrolled eye movements)
• Cognitive impairment (confusion)
• Hirsutism (excess hair growth)
• Gingival hyperplasia (overgrowth of gums - very characteristic)
• Coarsening of facial features
• "Purple glove syndrome" with IV use - the hand turns purplish-black with swelling and pain at injection site
• Teratogen (causes birth defects - "fetal hydantoin syndrome": cleft lip, cleft palate)
• Uses zero-order kinetics at higher doses (small dose increase = large blood level jump - dangerous)
• Can worsen absence seizures

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2. Carbamazepine (Tegretol)

• Tricyclic structure (similar to antidepressants) - also used for bipolar disorder
• Mechanism: Same as phenytoin (Na+ channel blocker, inhibits rapid firing). Also blocks norepinephrine uptake, potentiates GABA effects

• Nausea and visual disturbances
• Autoinduction of metabolism (the drug speeds up its own breakdown over time - dose may need adjustment)
• Granulocyte suppression (low white blood cells)
• Aplastic anemia (bone marrow failure - rare but serious)
• Worsens absence seizures

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3. Oxcarbazepine

• Very similar to carbamazepine but safer side effect profile
• Same mechanism (Na+ channel blocker)
• Has an active metabolite that does the work
• Side effects: Mainly hyponatremia (low sodium) - fewer hypersensitivity reactions and less enzyme induction than carbamazepine

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4. Phenobarbital

• The oldest antiseizure drug overall
• Effective but causes sedation - often reserved for infants
• Mechanism: Prolongs the opening of chloride (Cl-) channels (GABA-A receptor) - increases inhibition. Also blocks glutamate (AMPA) receptors

• Sedation (most prominent)
• Cognitive impairment
• Behavioral changes (especially in children)
• Induces liver enzymes (affects metabolism of many other drugs)
• Can worsen absence and atonic seizures

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5. Primidone

• Gets converted in the body to phenobarbital (and PEMA) - both active
• Works similarly to phenobarbital
• Must be started at low dose to avoid early sedation and stomach upset

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6. Valproate (Valproic Acid)

• One of the most widely used antiseizure drugs
• Mechanism similar to phenytoin (Na+ blocker) PLUS increases GABA levels in the brain (by facilitating GAD and inhibiting GABA transporter GAT)
• Effective for many seizure types including absence and generalized

• Elevated liver enzymes, rare severe hepatotoxicity (liver failure - especially in young children)
• Nausea, vomiting, abdominal pain
• Tremor, hair loss, weight gain
• Teratogen (major concern in women of childbearing age)
• Many interactions with other antiseizure drugs

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7. Ethosuximide (Zarontin)

• Drug of choice for absence seizures (petit mal)
• High efficacy, good safety profile
• Mechanism: Blocks T-type calcium channels in thalamic neurons - this stops the 3/sec oscillation that causes absence seizures. Also inhibits Na+/K+ ATPase at high doses

• Stomach upset, nausea, vomiting
• Lethargy, fatigue, headache
• Hiccups, euphoria
• Skin rash, lupus-like syndrome (rare)

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8. Clonazepam (Klonopin)

• A benzodiazepine (same family as diazepam)
• One of the most potent antiseizure drugs known
• Long-acting
• Mechanism: Increases frequency of Cl- channel openings (GABA-A receptor boost)
• Used for absence, myoclonic seizures, infantile spasms

• Sedation (most prominent)
• Ataxia
• Behavioral disorders

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9. Vigabatrin

• Mechanism: Irreversibly blocks GABA-aminotransferase (the enzyme that breaks down GABA) → GABA builds up → more inhibition
• Used for partial seizures and West's syndrome (infantile spasms)
• Contraindicated in patients with pre-existing mental illness

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10. Lamotrigine

• Well absorbed, long half-life (24 hours)
• Mechanism: Blocks voltage-dependent sodium channels (use-dependent) - stabilizes neuronal membranes
• Effective for partial and many generalized seizures including absence and myoclonic

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11. Topiramate

• Mechanism: Multiple - blocks Na+ channels + potentiates GABA (at different site than BZDs/barbiturates) + blocks kainate/AMPA glutamate receptors
• Broad-spectrum antiseizure drug
• Teratogenic in animal models

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12. Tiagabine

• Mechanism: Blocks GAT-1 (GABA transporter 1) - prevents reuptake of GABA from the synapse → GABA stays longer → more inhibitory effect
• Used for partial and generalized tonic-clonic seizures

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13. Gabapentin & Pregabalin

• Structurally similar to GABA but do NOT act on GABA receptors
• May alter GABA metabolism and transport
• Used as add-on therapy for partial seizures
• No liver enzyme induction, no protein binding, minimal drug interactions

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14. Perampanel

• Mechanism: Blocks AMPA receptors (a type of glutamate receptor) - reduces excitation
• Very long half-life: 70-110 hours
• Highly protein bound (95%)

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15. Felbamate

• Effective against partial seizures
• But has very severe side effects - now used only as last resort (3rd-line) for treatment-resistant cases

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16. Lacosamide

• Sodium channel blocker - specifically for focal (partial) seizures

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PART 9: Drugs for Special/Rare Epilepsies

Dravet Syndrome (Severe Myoclonic Epilepsy of Infancy)

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PART 10: Other Newer Drugs (Brief)

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Quick Summary Table

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