(3.11) Pharmacotherapy of seizure disorders Flashcards
What are risk factors for seizure reccurrence?
- <2 yrs seizure free
- Onset of seizure after age 12
- Hx of atypical febrile seizures
- 2-6 yrs before good seizure control in tx
- > 30 seizures before controlled
- Partial seizures (most common)
- Abnormal EEG
- Organic neurological disorder
- Withdrawal of phenytoin or valproate
What is drug resistant epilepsy?
Failure of at least 2 trials of antiseizure meds of adequate dose and duration
What are possible reasons for tx failure in drug resistant epilepsy?
- Failure to reach CNS target
- Alteration of drug targets in CNS
- Drugs missing the real target
What are management strategies of drug resistant epilepsy?
- Rule out pseudo-resistance (wrong drug or diagnosis)
- Combination therapy
- Electrical/surgical intervention
What is status epilepticus?
Continuous seizure activity lasting 5 minutes or more, or two or more discrete seizures w incomplete recovery between seizures
What dosage form is most commonly used for status epilepticus?
IV
What is the most common drug class used for status epilepticus?
Benzodiazepines, most commonly lorazepam or midazolam
When is fosphenytoin used?
In the second or third treatment phase of status epilepticus
What is an issue with phenytoin?
Contains propylene glycol - can cause hypotension and this limits infusion rate
What is fosphenytoin?
Prodrug of phenytoin, better IV tolerance of dosing
What is the loading dose of fosphenytoin?
- 20 mg PE (phenytoin equivalents)/kg IV, may give additional dose 10 minutes after load
- Up to 150 mg PE/min IV infusion
What is the monitoring parameter with phenytoin/fosphenytoin?
Cardiac monitoring required, may also cause local rxn called “purple glove syndrome”
What must be obtained in the same blood draw (oral phenytoin dosing considerations)?
MUST obtain both phenytoin serum conc and serum albumin
What is the equation for adjusted conc (oral phenytoin dosing considerations)?
What is the therapeutic serum conc range (oral phenytoin dosing considerations)?
10-20 mcg/ml
What does it mean if there the unadjusted conc falls within the therapeutic range?
There is unbound phenytoin within the therapeutic range of 1-2 mcg/ml
What is the IV to PO conversion of valproate?
1:1 mg/mg
What is the desired serum concentration of valproate?
80 mcg/ml (range 50-125 mcg/ml)
Which drugs are 1A2 inducers?
- Carbamazepine
- Phenobarbital
- Phenytoin
Which drugs are 2C9 inducers?
- Cabamazepine
- Phenobarbital
- Phenytoin
Which drugs are 3A4 inducers?
- Carbamazepine
- Lamotrigine
- Oxcarbazepine
- Phenobarbital
- Phenytoin
- Topiramate
Which drug is a UGT inhibitor?
Valproate
What is the dosing of lamotrigine?
What is the black box warning prior to initiating carbamazepine or derivatives?
Genetic screen for HLA-B*1502 allele due to anticonvulsant hypersensitivity syndrome
Can HLA-B*1502 allele positive pts be treated with carbamazepines or derivatives?
NO unless benefit clearly outweigh the risk
There is a strong correlation for positive HLA-B*1502 allele and anticonvulsant hypersensitivity syndrome in ppl of what descent?
Asian descent
What other allele may confer similar risk to HLA-B*1502 and anticonvulsant hypersensitivity syndrome?
Positive HLA-A*3101 in those of Northern European and Asian descent
What is the outlook and mortality rate of DRESS syndrome?
Potentially life threatening - estimated mortality rate of 10%
When does DRESS syndrome occur?
Generally, occurs 2-6 wks after initiation of drug therapy