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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Side-by-side3 compared
Focus
Comparevs
Dimension
Phenytoin
Valproic Acid
Levetiracetam
Class & mechanism
- Na⁺-channel blocker (hydantoin)
- ↑ GABA
- Na⁺/Ca²⁺ multi-mechanism
- Binds SV2A synaptic vesicle protein
Indications
- Tonic-clonic & focal (not absence)
- Absence, myoclonic, tonic-clonic
- Also bipolar & migraine prophylaxis
- Focal & generalized, mono or adjunct
Route & administration
- PO/IV
- IV ≤ 50 mg/min on cardiac monitor
- Mix in NS only (precipitates in D5W)
- PO/IV
- Take with food for GI upset
- PO/IV
- Renal dosing; no slow titration
Key assessment
- Monitor seizure frequency & type
- Nystagmus, ataxia, slurred speech
- Monitor seizure frequency & type
- Tremor, ↑ ammonia, weight gain
- Monitor seizure frequency & type
- Mood, irritability, behavior changes
Monitoring labs
- ★Level 10–20 mcg/mL (narrow range)
- Level 50–100 mcg/mL
- LFTs, ammonia, platelets
- No routine drug levels needed
Adverse effects
- ★Gingival hyperplasia
- Hirsutism, coarse facial features
- Drowsiness, dizziness
- Weight gain, alopecia, GI upset
- Drowsiness, dizziness
- Drowsiness, dizziness
Black box & toxicity
- Purple glove syndrome (IV extravasation)
- Rapid IV: hypotension, arrhythmias
- Suicidal ideation risk (all AEDs)
- ★Hepatotoxicity & pancreatitis (black box)
- Report N/V, abdominal pain, jaundice
- Suicidal ideation risk (all AEDs)
- Suicidal ideation risk (all AEDs)
Contraindications & interactions
- CYP inducer: ↓ OCP & warfarin effect
- ★Most teratogenic: neural tube defects
- Few drug interactions
Patient teaching
- Do not stop abruptly
- Meticulous gum care
- Stay on the same brand
- Report rash (SJS risk)
- Do not stop abruptly
- Report rash (SJS risk)
- Do not stop abruptly
- Report rash (SJS risk)
Class & mechanism
Phenytoin
- Na⁺-channel blocker (hydantoin)
Valproic Acid
- ↑ GABA
- Na⁺/Ca²⁺ multi-mechanism
Indications
Phenytoin
- Tonic-clonic & focal (not absence)
Valproic Acid
- Absence, myoclonic, tonic-clonic
- Also bipolar & migraine prophylaxis
Route & administration
Phenytoin
- PO/IV
- IV ≤ 50 mg/min on cardiac monitor
- Mix in NS only (precipitates in D5W)
Valproic Acid
- PO/IV
- Take with food for GI upset
Key assessment
Phenytoin
- Monitor seizure frequency & type
- Nystagmus, ataxia, slurred speech
Valproic Acid
- Monitor seizure frequency & type
- Tremor, ↑ ammonia, weight gain
Monitoring labs
Phenytoin
- ★Level 10–20 mcg/mL (narrow range)
Valproic Acid
- Level 50–100 mcg/mL
- LFTs, ammonia, platelets
Adverse effects
Phenytoin
- ★Gingival hyperplasia
- Hirsutism, coarse facial features
- Drowsiness, dizziness
Valproic Acid
- Weight gain, alopecia, GI upset
- Drowsiness, dizziness
Black box & toxicity
Phenytoin
- Purple glove syndrome (IV extravasation)
- Rapid IV: hypotension, arrhythmias
- Suicidal ideation risk (all AEDs)
Valproic Acid
- ★Hepatotoxicity & pancreatitis (black box)
- Report N/V, abdominal pain, jaundice
- Suicidal ideation risk (all AEDs)
Contraindications & interactions
Phenytoin
- CYP inducer: ↓ OCP & warfarin effect
Valproic Acid
- ★Most teratogenic: neural tube defects
Patient teaching
Phenytoin
- Do not stop abruptly
- Meticulous gum care
- Stay on the same brand
- Report rash (SJS risk)
Valproic Acid
- Do not stop abruptly
- Report rash (SJS risk)
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Clinical Pearl
Phenytoin = check levels and gums; valproic acid = check the liver; Keppra = check the mood.
Component Topics
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