Antiepileptics

Question 0

Phenobarbital

Answer 0

Level should be between 20 and 40 µg/ml

Toxicity can occur above those levels and lead to more seizures

Question 1

Therapy

Answer 1

Can use any antiepileptic for any seizure except absence which requires valproic acid or ethosuximide

Drugs:

1. Modulate sodium channels: phenobarbital (luminal), phenytoin (dilantin), carbamazepine (Tegretol), valproic acid (Depakene), divalproex (Depakote)
2. Modulate calcium channels: ethosuximide
3. Unknown mechanism: primidone (mysoline) and levetiracetam (Keppra)
4. Inhibit glutamate channels: Felbamate (felbatol)
5. Multiple mechanisms: gabapentin (Neurontin) and topiramate (Topamax)

Question 2

Phenytoin or Dilantin

Answer 2

Do not exceed 50 mg per minute (level should be between 10 to 20 µg per mill total or 1 to 2 mcg/mL of free

Side effects: lupus syndrome, cardiovascular effects such as hypertension, and gingival hyperplasia

Similar drug: fosphenytoin or cerebrex (1.5 mg of fosphenytoin is equal to 1 mg of phenytoin and is ordered and phenytoin equivalents) (note: kinetics are unpredictable for fosphenytoin-zero order)

Question 3

Carbamazepine or Tegretol

Answer 3

Could make myoclonic seizures worse

This medication is an auto inducer and lowers its own levels

Side effects are huge: hepatitis, agranulocytosis, infection, thrombocytopenia, SIADH

Question 4

Antiepileptics that must be renally adjusted

Answer 4

Keppra and Neurontin

Question 5

Least likely to cause a seizure

Answer 5

All antiepileptics are associated with seizure potential but gabapentin is the least likely

Question 6

Target drug concentrations in order

Answer 6

Carbamazepine: 6 to 10 mcg/mL (same as mg/L)
Phenobarbital: 20 to 40 mcg/mL
Ethosuximide: 50 to 100 mg/L
Approac acid: 50 to 100 mg/L

Question 7

Antiepileptic not associated with CYP Interactions

Answer 7

Levetiracetam or Keppra