Week 1 Antiepileptic 1 of 4 Flashcards
collective term used to designate a group of chronic CNS disorders characterized by the onset of sudden disturbances of sensory, motor, autonomic, or psychic origin:
epilepsy
Epilepsy is generally transient with what exception?
status epilepticus
what % of people will report at least one seizure in their lifetime?
10%
What % of worldwide population meets the dx criteria for epilepsy?
1-2%
Classification of epileptic seizures Table 13-1:
1.) Partial Seizures (beginning locally):
- Simple partial seizures (consciousness not impaired)
- Complex partial seizures (consciousness impaired)
- Partial seizures evolving into secondary generalized seizures
Classification of epileptic seizures Table 13-1:
2.) Generalized Seizures (non-convulsive & convulsive):
- Absence seizures (petit mal)
- Myoclonic seizures
- Clonic Seizures
- Tonic seizures
- Tonic-clonic seizures
**and there are “unclassified seizures”
30% of pts with seizures have
an identifiable neurologic or systemic d/o
**Epilepsy Tx goal:
control seizures w/minimal medication related adverse effects
70% of pts w/epilepsy will be seizure free using
a single epileptic drug
30% of pts w/epilepsy may require
- transitioning to another drug
- combining w/primary drug
- vagal nerve stimulator
- neurosurgical resection
With drug failure, epileptic pts may use:
- vagal nerve stimulator
- Neurosurgical resection
antiepileptic medications becoming more preferred by patients are
sustained released
GI absorption is
slow (over hours) and may be incomplete
Protein binding varies greatly.
Name least and greatest?
- Gabapentin 0%
- Phenytoin >= 90%
What may necessitate dose adjustments?
hepatic and renal disease
Name antiepileptic medications that rely on RENAL excretion:
- Gabapentin*
- Levetiracetam*
- Pregabalin*
- Vigabatrin
- Zonisamide
*remaining drugs should be dosed according to pts liver dysfunction
Drugs with clearance/elimination half time ranges from HOURS:
- Carbamazepine
- Gabapentin
- Primidone
- Valproate
Drugs with clearance/elimination half time ranges from DAYS:
- Lamotrigine
- Phenytoin
- Phenobarbital
- Zonisamide
antiepileptic drugs all have the ability to do what to drug metabolism?
induce or inhibit
All antiepileptic drugs may be associated with interactions (resulting interactions of plasma drug concentrations) EXCEPT:
- Gabapentin
- Levetiracetam
- Vigabatrin
“GLV” “gotta love Vigabatrin” (so not to mix up with valproate if he tried to trick!)
Highly bound protein drugs:
- Carbamazepine
- Phenytoin
- Valproate
VCP - “very competitive Proteins”
What is significant about antiepileptic and protein binding drug interactions?
medications that compete for pr binding sites of highly bound antiepileptic drugs can displace them.
- increasing plasma levels of pharmacologically active antiepileptic drugs
Name some commonly used highly pr bound medications used:
- Salicylates
- Thyroxine
- Phenylbutazone
why is Phenylbutazone (NSAID) no longer used in the US?
- highly pr bound
- bone marrow suppression and dangerously low WBC
The principle binding site for antiepileptic drugs is?
Albumin
Hypoalbuminemia my be seen in what kinds of patients?
- renal or hepatic disease
- malnutrition
- book says pregnancy as well*
Hypoalbuminemia in a pt taking antiepileptics may result in:
- increased plasma concentrations of unbound antiepileptic drug
- resulting in TOXICITY despite therapeutic plasma concentrations
hypoalbuminemia in pregnancy is due to
progressive increase in central volume
(Increased plasma volumes
- this is more dilutional
dosing for antiepileptic medications should be
gradual dose titration
-except in an emergency
Dosing for antiepileptics is guided by
clinical response over time
Noncompliance is high in
elderly and adolescents
failure to achieve sufficient high plasma concentrations is
medication ineffectiveness
Dosing at 1/2 the drug’s elimination half time ensures what?
$$ Exam Q$$
that a single dose missed will not result in sub-therapeutic plasma concentrations (pt won’t have a seizure)
to ensure that a single missed dose of an antiepileptic medication will not result in a sub-therapeutic level (or induce a seizure), what is done?
dosing at 1/2 the drug’s elimination half-time
$$
Review Table 13-2: MOA, Targeted Seizure, Dosage
Carbamazepine Gabapentin Phenobarbital Phenytoin Topiramate Valproate
- Carbamazepine - Na-ch blockade; partial seizures; 10-40mg/kg/day 2-3x day
- Gabapentin - Unknown MOA (?increases GABA release?); partial/generalized seizures; 10-60 mg/kg/day
- Phenobarbital: Cl-ch; P&G seizures; 2-5mg/kg/day every day in two doses
- Phenytoin: Na-ch blockade; Ca-ch; NMDA receptors; P&G; 3-7mg/kg/day in 3 doses
- Topiramate: Na-ch blockade, enhanced GABA activity, Ca-ch blockade; P&G; 500-3000mg/day in 2-4 divided doses
- Valproate: Na-ch blockade; Ca-ch; P&G; 500-3000mg/day in 2-4 divided doses
which antiepileptic drug requires routine (lab) monitoring?
Phenytoin
Titration to _____ is recommended for guiding the ______ of antiepileptic drugs.
- clinical efficacy
- dosages
If a pt is not responding as expected what is done?
-plasma drug levels may help determine compliance and pharmacokinetic interactions
for most patients, epileptic seizure activity has a
localized or focal origin
The cause for high frequency and synchronous firing in a seizure focus:
- is usually unknown Possible Explanations: local biochemical changes Ischemia loss of cellular inhibitory systems Infection Head trauma
Neurons in a chronic seizure focus exhibit
denervation hypersensitivity with regard to excitatory stimuli
Normal Inhibitory mechanisms presumably restrain
the spread of seizure activity to neighboring normal cells
Factors that may facilitate the spread of a seizure focus into areas of the normal brain:
-Blood glucose concentrations
-PaO2
-PaCO2
-pH
Endocrine fxn
-Stress
-Fatigue
-Electrolyte balance
If the spread of a seizure focus is extensive enough what can occur?
- the entire brain is activated
- tonic-clonic seizure with unconsciousness
If the spread of seizure focus is localized the seizure produces
s/s characteristic to the area of anatomic focus
Once a seizure is initiated it’s likely to be maintained by:
reentry of EXCITATORY impulses in a closed feedback pathway (that may not even include the original seizure focus)
The brain is divided into:
two halves:
- right hemisphere
- left cerebral hemisphere
the left side of the brain controls the
right side of the body
the right side of the brain controls the
left side of the body
$$ What part of the brain controls muscle movements, thinking, and JUDGMENT?
Frontal lobe
$$ What part of the brain controls sense of Touch, response to Pain and Temperature, and understanding of language?
Parietal lobe
$$ What part of the brain controls vision?
Occipital lobe
$$ What part of the brain controls hearing and memory?
Temporal lobe
$$ What part of the brain controls balance?
Cerebellum
$$ What part of the brain controls breathing and regulates Heartbeat?
Brain Stem
The frontal lobe controls:
muscle movements, thinking, and JUDGMENT
Parietal lobe controls:
sense of touch, response to pain/temp and understanding of language
the occipital lobe controls:
vision
the temporal lobe controls:
hearing and memory
the cerebellum controls:
balance
the brain stem controls:
breathing and heartbeat regulation
-“life sustaining”
MOA of antiepileptic drugs is not completely understood.
- It may control seizures by:
- This may be achieved by:
control by:
- decreasing neuronal excitability or
- enhancing inhibition of neurotransmission
Achieved by:
- altering intrinsic membrane ion currents (na, k, Ca) conductance or
- by affecting activity of inhibitory NT’s
What ion currents are primarily affected by antiepileptic drugs?
voltage-gated sodium and
calcium channels
Drugs that delay reactivation of Na-channels during high frequency neuronal firing produce;
an inhibitory effect on creation of AP’s until neuronal d/c is blocked
Name some antiepileptic drugs that act on the Na-Channels:
1-Carbamazepine 2-Lamotrigine 3-Phenytoin 4-Primidone 5-Valproate
Name some antiepileptic drugs that act on BOTH Na and Ca channels:
1- Carbamazepine
2-Lamotrigine
3- Phenytoin
4-valproate
Name some antiepileptic drugs that act selectively on ca channels
- Ethosuximide
2. phenobarbital
Drugs that alter synaptic function act primarily by
enhancing GABA mediated neuronal inhibition
$$ Phenobarbital (and other barbiturates) increase the:
Duration of GABA ion channel openings
$$ Benzodiazepines increase
frequency of GABA mediated ion channel openings
$$ What is the difference b/w Phenobarbital and benzodiazepines and their MOA on the GABA ion channels?
Phenobarbital - increases DURATION of channel opening
Benzo’s - increase the FREQUENCY of channel openings
Tiagabine effectively enhances GABA-mediated neuronal inhibition after synaptic release of the NT by doing what?
Delaying the REUPTAKE of GABA from synaptic clefts
what drug delays the reuptake of GABA from the synaptic clefts to effectively enhance GABA inhibition?
Tiagabine