multi class comparison

Antiepileptic Drug Comparison: Phenytoin vs Valproic Acid vs Levetiracetam — Levels, Toxicity, Monitoring

Three anticonvulsants, three completely different monitoring burdens. Phenytoin's narrow therapeutic window makes toxicity a constant threat, valproic acid quietly destroys livers, and levetiracetam tricks students into ordering labs it doesn't need. Picking the wrong monitoring plan on the NCLEX costs you the question.

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Comparison

Side-by-side3 compared
Comparevs
Dimension
Phenytoin
Valproic Acid
Levetiracetam
Class & mechanism
  • Na⁺-channel blocker then stabilizes neurons
  • ↑ GABA
  • Na⁺/Ca²⁺ multi-mechanism
  • Binds SV2A synaptic vesicle protein
Indications
  • Tonic-clonic & status epilepticus
  • Broad: absence, myoclonic, tonic-clonic
  • Also bipolar & migraine prophylaxis
  • Broad-spectrum adjunct
  • partial & tonic-clonic
Route & administration
  • PO/IV
  • IV slow
  • NORMAL SALINE only (precipitates in D5W)
  • PO/IV
  • take with food for GI upset
  • PO/IV
  • renal dosing, no titration delay
Key assessment
  • Monitor seizure frequency & type
  • Ataxia, nystagmus, slurred speech (toxicity)
  • Monitor seizure frequency & type
  • Tremor, ↑ ammonia, weight gain
  • Monitor seizure frequency & type
  • Mood, irritability, behavior changes
Monitoring labs
  • ★Level 10–20 mcg/mL — narrow therapeutic
  • Level 50–100 mcg/mL
  • LFTs & ammonia
  • No routine drug levels needed
Adverse effects
  • ★Gingival hyperplasia
  • Hirsutism, coarse facial features
  • Weight gain, alopecia, GI upset
  • Somnolence, dizziness, fatigue
Black box & toxicity
  • Purple glove syndrome with IV extravasation
  • ★Hepatotoxicity & pancreatitis (black box)
  • Report Nausea/vomiting, abdominal pain, jaundice
  • Suicidal ideation risk (all antiepileptics)
Contraindications & interactions
  • Strong CYP inducer then ↓ OCP & warfarin
  • ★Pregnancy — neural tube defects (teratogen)
  • Few drug interactions
  • renal impairment
Patient teaching
  • Do not stop abruptly (status epilepticus)
  • Meticulous gum care
  • keep same brand
  • Do not stop abruptly (status epilepticus)
  • Report rash (SJS risk)
  • Do not stop abruptly (status epilepticus)
  • Report rash (SJS risk)
Class & mechanism

Phenytoin

  • Na⁺-channel blocker then stabilizes neurons

Valproic Acid

  • ↑ GABA
  • Na⁺/Ca²⁺ multi-mechanism
Indications

Phenytoin

  • Tonic-clonic & status epilepticus

Valproic Acid

  • Broad: absence, myoclonic, tonic-clonic
  • Also bipolar & migraine prophylaxis
Route & administration

Phenytoin

  • PO/IV
  • IV slow
  • NORMAL SALINE only (precipitates in D5W)

Valproic Acid

  • PO/IV
  • take with food for GI upset
Key assessment

Phenytoin

  • Monitor seizure frequency & type
  • Ataxia, nystagmus, slurred speech (toxicity)

Valproic Acid

  • Monitor seizure frequency & type
  • Tremor, ↑ ammonia, weight gain
Monitoring labs

Phenytoin

  • ★Level 10–20 mcg/mL — narrow therapeutic

Valproic Acid

  • Level 50–100 mcg/mL
  • LFTs & ammonia
Adverse effects

Phenytoin

  • ★Gingival hyperplasia
  • Hirsutism, coarse facial features

Valproic Acid

  • Weight gain, alopecia, GI upset
Black box & toxicity

Phenytoin

  • Purple glove syndrome with IV extravasation

Valproic Acid

  • ★Hepatotoxicity & pancreatitis (black box)
  • Report Nausea/vomiting, abdominal pain, jaundice
Contraindications & interactions

Phenytoin

  • Strong CYP inducer then ↓ OCP & warfarin

Valproic Acid

  • ★Pregnancy — neural tube defects (teratogen)
Patient teaching

Phenytoin

  • Do not stop abruptly (status epilepticus)
  • Meticulous gum care
  • keep same brand

Valproic Acid

  • Do not stop abruptly (status epilepticus)
  • Report rash (SJS risk)

★ marks the fact that sets a column apart.

Clinical Pearl

Phenytoin = check levels and gums; valproic acid = check the liver; Keppra = check the mood.

Component Topics

Levetiracetam & Newer AntiepilepticsPhenytoin / DilantinValproic Acid / Depakote

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