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.
Comparison
Side-by-side3 compared
Comparevs
Dimension
Phenytoin
Valproic Acid
Levetiracetam
Class & mechanism
- Na⁺-channel blocker → 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 N/V, abdominal pain, jaundice
- Suicidal ideation risk (all antiepileptics)
Contraindications & interactions
- Strong CYP inducer → ↓ 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 → 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 N/V, abdominal pain, jaundice
Contraindications & interactions
Phenytoin
- Strong CYP inducer → ↓ 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.
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