Tonic-Clonic Seizure: Pharmacological Algorithm and Management

Overview

PHASE 0 - Immediate Stabilization (0-5 min)

• Protect airway; position patient laterally (recovery position)
• Administer supplemental oxygen; prepare for intubation if needed
• Insert IV line; draw blood glucose, electrolytes, drug levels, toxicology screen
• Give 50% dextrose (50 mL IV) + thiamine 100 mg IV if hypoglycemia suspected or alcohol history
• Monitor blood pressure, cardiac rhythm, oxygen saturation
• Assess for head/cervical injury if onset unwitnessed

PHASE 1 - First-Line: Benzodiazepines (0-10 min)

Key point: Early treatment is decisive. Intramuscular midazolam is slightly superior to IV lorazepam in the prehospital setting simply because IV line placement causes delay. Benzodiazepines alone terminate seizures in ~70% of early SE. - (Goldman-Cecil Medicine; Katzung's Basic & Clinical Pharmacology, 16th Ed.)

PHASE 2 - Second-Line: Established SE (10-30 min)

Note from Harrison's Principles of Internal Medicine 22E: Lamotrigine, valproic acid, and levetiracetam are the best initial chronic choices for primary generalized tonic-clonic epilepsy. Valproate is superior to levetiracetam for newly diagnosed generalized epilepsy.

PHASE 3 - Refractory SE (>30 min after first- and second-line failure)

Titrate all anesthetic agents to EEG burst-suppression. Every 12-24 hours, slow the infusion to reassess. Consider neuromuscular blockade only with continuous EEG monitoring (paralysis masks clinical seizure activity). - (Adams and Victor's Principles of Neurology; Goldman-Cecil Medicine)

PHASE 4 - Super-Refractory SE (>24h of anesthesia, seizures recur on withdrawal)

• Reinstate general anesthesia
• Allopregnanolone (neurosteroid) - modulates synaptic and extrasynaptic GABA-A receptors
• Isoflurane inhalational anesthesia (impractical in most ICUs)
• Ketogenic diet (adjunctive, especially in pediatric/young adult cases)
• Immune therapy (steroids, IVIG, plasmapheresis) if autoimmune etiology suspected

Long-Term Oral Maintenance Therapy for Chronic GTCS/Epilepsy

For Primary Generalized Tonic-Clonic Seizures:

• First-line: Lamotrigine, Valproic acid, Levetiracetam (Harrison's, 22E)
• Alternatives: Topiramate, Zonisamide, Perampanel
• Avoid: Carbamazepine, Oxcarbazepine, Phenytoin (can worsen primary generalized epilepsy)

For Focal-onset Seizures with Secondary Generalization:

• First-line: Lamotrigine (superior to levetiracetam and zonisamide for focal epilepsy)
• Alternatives: Valproate, Levetiracetam, Carbamazepine, Lacosamide, Brivaracetam, Gabapentin

Drug Selection Considerations:

Practical Summary Algorithm

Seizure begins
    |
    v
>5 minutes (or uncertain duration)
    |
    v
[PHASE 1] Benzodiazepine
  IV Lorazepam 0.1 mg/kg  OR  IM Midazolam 10 mg (prehospital)
  Can repeat ONCE
    |
    | Seizure persists >5-10 min
    v
[PHASE 2] Second-line agent (choose one):
  Fosphenytoin 15-20 mg PE/kg  OR  Valproate 30-40 mg/kg  OR  Levetiracetam 60 mg/kg
  (Phenobarbital 10 mg/kg if above unavailable)
    |
    | Seizure persists >30 min
    v
[PHASE 3] REFRACTORY SE — Admit ICU
  Midazolam infusion  OR  Propofol infusion  OR  Pentobarbital coma
  Continuous EEG monitoring
    |
    | Seizures recur >24h
    v
[PHASE 4] SUPER-REFRACTORY SE
  Reinstate anesthesia; consider ketamine, neurosteroids, ketogenic diet,
  immune therapy if autoimmune etiology
    |
    v
After control: Start oral long-term ASD
  (Lamotrigine / Valproate / Levetiracetam for generalized epilepsy)

Key Monitoring Points

• ECG before phenytoin/fosphenytoin and lacosamide
• Blood pressure during IV benzodiazepines at higher rates
• EEG continuous in refractory/super-refractory SE and during neuromuscular paralysis
• Serum drug levels to guide dosing (though clinical response is the primary guide)
• Liver function and CBC for valproate; especially critical in children <2 years

• Adams and Victor's Principles of Neurology, 12th Ed. - Treatment of Convulsive Status Epilepticus (Table 15-8)
• Katzung's Basic and Clinical Pharmacology, 16th Ed. - Status Epilepticus chapter
• Goldman-Cecil Medicine (International Ed.) - Status Epilepticus section
• Harrison's Principles of Internal Medicine, 22E (2025) - Antiseizure Drug Selection for Generalized Seizures
• AES Clinical Guidance - American Epilepsy Society evidence-based guidelines

Recent evidence note: A 2025 systematic review (PMID 40876407) confirms that intramuscular midazolam and IV lorazepam have comparable effectiveness for pediatric status epilepticus, supporting the prehospital IM midazolam preference outlined above.