ANTIEPILEPTICS Flashcards
Seizures
TRANSIENT alteration of behavior due to disordered, synchronous and rhythmic firing
Epilepsy
Sudden recurrent attacks of motor, sensory, autonomic, psychic
Motor component is the
Seizure
Epilepsy classification
Partial (focal) : begin one hemisphere of the brain
Generalized seizures
Simple partial
no LOC
Complex partial seizures
Loss of concsciousness
Partial with secondary generalized seizures
evolves to both sides of the brain, convulsive seizure.
Generalized seizures begin where?
both hemispheres of the brain and usually result in LOC
Absence seizures also known as
petit mal
Types of generalized
absence myoclonic tonic-clonic tonic clonic atonic (akinetic) Status epilepticus
Status Epilepticus
any seizure that last more than 20 minutes OR
seizures of sufficient frequency that the patient does not regain consciousness between episodes.
Status Epilepticus
more than 30-60 minutes –> CNS damage
Give first in SE
fast acting medications f/B
Longer acting
Neuromuscular blocking drugs are
CONTRAINDICATED or not the first drug of choice for SE
DO not stop seizure
NMB
Drug of choice for Absence seizure
Ethosuximide
Stratus Epilepticus first line for treatment
LORAZEPAM - CHOICE drug
Anti-epileptic and drug interactions
no effect on these meds.
Chronic anticonvulsant therapy are resistant Nondepolarzing NMJ such as ROCURONIUM (INCREASE rate)
No effect on ATRACURIUM, MIVACURIUM, CISATRACURIUM
Patients being treated with AEDs have increased dose requirement
THIOPENtAL
PROPOFOL
MIDAZOLAM
OPIODS
AED numbers interaction gbecause
Highly metabolized in the liver
They are inducers/ inhibitors or both
Highly protein bound to this protein
ALBUMIN
For those AED agents that are highly protein bound,
displacement from binding site by other highly poroten bound drugs can occur and lead to increase plasma concentration of the AED medications
HYPOALBUMINIA can results in INCREASE PLASMA CONCENTRATION of unbound AED, resulting in toxicity
Acute administration of phenytoin
Prolong Non-Depolarizing neuromuscular blockers
Decrease glutamate (excitatory neurotransmitter) synaptic activity
NMDA (N-methyl-D-aspartate) receptor antagonists
• AMPA/kainate receptor antagonist
4. Inhibition of brain carbonic anhydrase enzyme
Enhance GABA-mediated neuronal inhibition synaptic activity
- GABA (γ-aminobutyric acid) modulators/enhancers
- GABA (γ-aminobutyric acid) re-uptake inhibitors
- GABA (γ-aminobutyric acid) transaminase inhibitors
• Antiepileptic drugs (AEDs) exert their anticonvulsant activity by
the following proposed general mechanisms:
.
- Inactivate either voltage-gated Na+ or voltage-gated Ca++ currents
via blockade. Some AEDs can inactive both currents
2.Enhance GABA-mediated neuronal inhibition synaptic activity - Decrease glutamate (excitatory neurotransmitter) synaptic activity
- Inhibition of brain carbonic anhydrase enzyme
AEDs and Pregnancy
- AEDs can cause teratogenic effects
- NEURAL TUBE defects such as spina bifida can occur, cleft lip & palate
- Phenobarbital, phenytoin, carbamazepine, valproic acid increase the incidence of congenital malformations
AVOIDED AT ALL COST in pregnancy
Phenobarbital, phenytoin, carbamazepine, valproic acid increase
the highest incidence of teratogenic malformations of all AEDs.
VALPROIC ACID
AED
First generation (Traditional, old) Second generation (newer)
Second generation AED
Pregabalin Lacosamide Rufinamide Vigabatrin, EGOzabine perampanel eslicarbazepine, and brivaracetam
Benzo
display anxiolytic, sedative, muscle relents
Benzo MOA
Potentiate GABA-mediated neuronal inhibition by binding to the benzodiazepine receptor site on GABAA receptors, which increases
the frequency of GABA-mediated ion channel opening and increases chloride permeability and thereby leads to cellular hyperpolarization and inhibition of neuronal firing
• Diazepam
•
Useful for treatment of status epilepticus
• Has a rapid onset and short duration of action
Diazepam VS LORAZEPAM
• Has a faster onset but has a shorter duration of action than
lorazepam since diazepam is more lipophilic (gets in and out of the
CNS faster than lorazepam)
Diazepam important
SEVERAL ACTIVE METABOLITES
First benzo for SE
LORAZEPAM
Lorazepam
onset, not as fast as diazepam still fast
Less liphophillic than diazepam
pHenytoin class________ class anti-epileptic agent
• Available in both
•
Hydantoin ;ORAL and IV formulations
Phenytoin MOA
Fast Na+ Channel Blocker
• Regulates neuronal excitability and prevents the spread of seizure
activity from a seizure focus by regulating Na+ across neuronal
membranes. The effect is mediated by a slowing of the rate of
recovery of the Na+ channel
• Associated with use-dependent blockade of Na+ channels
Pharmacological effects of Phenytoin
Exerts anti-seizure activity without causing general depression of the CNS (usually not associated with excessive sedation) • In toxic cases, it may produce excitatory CNS signs & symptoms
Phenytoin is a (acid/base)
WEAK ACID
Phenytoin pharmacokinetics
Protein binding ____________
Half life
Half life increases if concentration is
Protein Binding: >90% protein bound
• Primarily bound to albumin
• Plasma t 1/2: 6-24 hours but the t1/2 increases when phenytoin’s
plasma concentration becomes > 10 mcg/mL
• Metabolism of Phenytoin
Liver via several CYP 450 enzyme systems
• Exhibits saturable metabolism OR Michaelis-Menten pharmacokinetics (a type of non-linear pharmacokinetics)
• Metabolized to inactive metabolites
• Excretion
with plasma concentrations < 10 mcg/mL, phenytoin follows
linear
pharmacokinetics
with plasma concentrations > 10 mcg/mL, the enzymes necessary for metabolism of phenytoin
pharmacokinetics (zero-order kinetics).
become saturated and the half-life
becomes dose-dependent and elimination follows non-linear
Target total concentration
10-20 mcg/ml (1-2mcg/ml)
CLASSIC ENZYME INDUCER
PHENYTOINC
METABOLIZED BY
multiple CYP 450 Enzymes
Phenytoin highly protein bound to
Albumin
Since phenytoin is metabolized by CYP 450 enzymes, administering phenytoin with CYP 50 inducers or inhibitors will alter phenytoin’s plasma
CYP 450 inducers will decrease phenytoin’s plasma concentrations
• CYP 450 inhibitors will increase phenytoin’s plasma concentrations
Administering other drugs that are bound to albumin will increase phenytoin’s free, unbound concentration and potentially increase the risk of toxicity
IM never an option for
Phenytoin
• IV infusion rate should NEVER exceed________
why?
exceed 50 mg/min
The propylene glycol diluent in the phenytoin injection dosage formulation is a known cardiac depressant and can cause severe hypotension, bradycardia and other cardiac arrhythmias if infused too fast!
IV infusion PHENYTOIN not to infused fast because of the
Diluent that’s in there
Watch drug-drug compatibility interaction so precipitation does not occur
• AVOID ______
• Phenytoin precipitates in solutions with ph of
dextrose solutions
pH < 7.8
CYP 450 inducers will (increase/decrease)
decrease phenytoin’s plasma concentrations
• CYP 450 inhibitors will (Increase/decrease)
increase phenytoin’s plasma concentrations
Non dose related phenytoin
Steven johnson Syndrome FETAL abnormalities (Fetal Hydantoin syndrome)
Fosphenytoin
prodrug of phenytoin
water soluble
INJECTABLE Only
Fosphenytoin routes
IV or IM
Once converted fosphenytoin is
highly protein bound
effect comes from phenytoin
Metabolism of phenytoin
by PHOSPHOTASE ENZYMES in the liver and RBCs
No drugs are known to
interferer with the metabolic conversion of fosphenytoin to phenytoin
Fosphenytoin compatible with either _____or _____
NS or D5W
Do not need IV filter for
Fosphenytoin
Fosphenytoin allow the administration of IV form
Faster
Loading dose of fosphenytoin
15-20 PE/Kg for SE
PE is PHENYTOIN Equivalents
Fosphenytoin and phenytoin is not a
1:1
Because of the risk of hypotension, administer fosphenytoin no faster than _______
150mg PE/min (3x as fast)
Carbamazepine (TegretoL)
TCA chemically
Oral agent
Tegretol vs phenytoin: 2 differences
1.Produces therapeutic responses in manic depressive patients
2 Has an anti-diuretic effect that is sometimes associated with increase concentration of ADH in the plasma
Mechanism of action tegretol
Fast Na+ channel blocker
THERE IS AN active metabolite
One of the Clinical uses of Tegretol for NON-SEIZURE
TRIGEMINAL NEURALGIA
Tegretol has a unique metabolic pathway
AUTO-INDUCER (induces its own metabolism)
Tegretol is metabolized by the liver to
an active metabolite, which is then burster metabolized into inactive metabolites & Excreted via urine
Tegretol requires
Adequate renal and liver function
Tegretol and CYP 450
Is a strong enzyme inducer of CYP450 and NON CYP 450 liver enzymes
Adverse effects of Tegretol
CAN CAUSE SIADH (water retention and hyponatremia)
Nondepolarizing NMB such as Vecu and rocuronium
May have resistance occur in patients CHRONICALLY receiving anticonvulsant agents such as tegretol or phenytoin
IF TEGRETOL is being used pre-operatively, patient will be resistant and is a KNOWN-GUARANTEED INTERACTION (standard dose of vec or ROC won’t work)
Will a standard dose of Nondepoleraizing NMB have safe effect of chronically treated patient
no
Phenobarbital is a
long acting barbiturates, oral
Phenobarbital MOA
binds to GABAa receptores via the barbiturate binding site and increases GABA mediated chloride influx.
Prolongs the opening of the chloride channels, which increases chloride influx , which intern increases membrane polarization (causes HYPERPOLARIZATION)
Phenobarbital has ______metabolites
NO ACTIVE METABOLITES
Phenobarbital half life is _______and about
80-100 hours
Phenobarbital metabolism
Interact with what system
CYP 450 Enzyme inducer and UGT enzymes system
Most common side effect of PHENOBARBital
Sedation, Sedation
What is primidone
Oral only anti-epileptic, prodrugs
2 active metabolites (phenobarbital and PEMA)
ETHOSUXIMIDE (succinimide)
oral only
100% bioavaillabitliy
0% protein binding
NO drugs to drug interaction
Ethosuximide type (maintenance)
T type Ca2+ channel blocker reduces the flow of Ca2+ through that fast channel.
Only clinical use of Ethosuximide
ABSENT SEIZURE
Valproic acid is
non-selective anti-seizure medication
CAN BE USED FOR MAJORITY OF SEIZURE BECAUSE MULTIPLE MECHANISM OF ACTION
Valproic acid MOA (4)
- fast Na+ Channel blocker
- T type Ca2+ blocker
- increases GABA production by stimulating GABA synthesis
- inhibiting GABA metabolism
Non seizure indication for valproic acid
Headache prevention
GI irritant drugs
Valproic acid , GI, GI
Valproic acid metabolism
Extensive metabolism in the liver,
NON dependent on CYP 450
Dependent on UGT enzymes
Has active metabolites.
What bad about valproic acid
- Lots of side effects
- drug to drug interactions
Valproic acid given with Phenytoin and diazepam
can displace and increase the free plasma concentration of those medication (phenytoin and diazepam)
Valproic acid and CYP 450
Strong enzyme inhibitor of CYP 450 and UGT enzymes
Valproic acid is an another drug that display
NON LINEAR PHARMACOKINETICS
This drug displays NON-LINEAR PHARMACOKINETICS
Valproic acid
Trileptal (oxcarbazepine)
prodrugs (not related to carbamezipine)
CONVERT TO ACTIVE METABOLITES that carries out reaction (10-monohydroxy metabolite)
Trileptal (oxcarbazepine) metabolism
ALWAYS eliminated
UGT enzymes (no auto induction) Phase II Glucuronide CONJUGATION and renal elimination
Trileptal (oxcarbazepine) metabolism
Fast Na+ Channel blocker
Trileptal (oxcarbazepine) both an enzyme
strong enzyme inducer/ inhibitor dependent on the pathway.
Trileptal can also causes
SIADH
Lamotrigine (Lamictal)
Broader spectrum of seizures
Exact mechanism of action of lamictal is
unknown
but decrease excitatory amino acids (glutamate and aspartate)
Protein binding of lamictal
half life is
55%
25 hours
Drug- Drug interaction : lamictal
- Not an inhibitor or inducer of CYP450
- Valproic acid decrease lamotrigine metabolism and increases its serum concentration and half life.
Hallmark of Lamictal
2 rashes and _____related
RASH (dose related) is the most serious potential adverse effect
2Stevens-Johnson Syndrome
Toxic Epidermal necrolysis (TEN)
Levetiracetam is a
Pure S-isomer ( not racemic)
FATAL and life threatening by which levetiracetam
Precise of MOA keppra
suggested binds to synaptic vesicle glycoprotein SV2A in the brain and alter its function and this may mediate the anticonvulsant activity
Absorption of Keppra is
100%
CLINICAL USES of Keppra
PREVENTION In surgical patients of seizure in some NEURO patients
Pharmacokinetics of Keepra (good drug because)
Excretion via ___________exclusive?
low protein bound
Not extensively metabolized.
ISSUE: EXCLUSIVE EXCRETION via kidneys
Brivaracetam (briviact)
expensive
Partial onset seizures in patients
SCHEDULED V meds (abuse potential)
Brivaracetma is same as keppra pharmacokinetics
100% oral bioavailability
Half life is 9 hours
Brivaracetam Metabolized through the
CYP450 Pathway
GABAPENTIN is a
Related to the neurotransmitter GABA but DOES NOT modify GABAa or GABAb ligand binding.
GABAPENTIN both a
Analgesic and antiepileptic drug
**MOA of GABAPENTIN
Bind to alpha 2 delta subunit of voltage dependent Ca2+ Channels, and inactivates them.
GABAPENTIN protein binding
low
NOT CYP450 dependent
Do not abruptly discontinue those 2 medications
GABAPENTIN, or lyrica
May have withdrawal syndrome
2 Clinical uses of gabapentin
POST HERPETIC NEURALGIA
Diabetic neuropathy
Pregabalin (LYRICA) is a derivative of
GABA and Chemically similar to gabapentin
Does NOT DIRECTLY BIND TO GABAa, GABAb,
DOES NOT AUGMENT Gabaa responses or have effects on GABA uptake or degradation
Lyrica
Schedules V
analgesic and antiepileptic effect
Same MOA as gabapentin (voltage gated Ca2+)
Low protein bound lyricA?
yes
CLINICAL use of lyrica
nerve pain syndrome
pain syndrome
ANESTHESIA IMPLICATIONS of GABAPENTIN
Decrease 3 things
when given ?
Side effects ; 3 possible
- Decrease opioid requirements/ consumption post op
- Decrease early post op pain
- Decrease post of N/V
Given typically 2 hours prior to surgey
can increase risk of dizziness, sedation, and confusion post op
Exact mechanism is known for the above effects.
Topiramate: Route Potentiates what? Enhances ? NO effects on \_\_\_\_\_\_
oral only
Fast voltage gated Na channel blocker
Enhances post synaptic GABAa, receptor currents.
low protein bound
Potentiates?
No effects on concentration of other medications
Decrease serum concentration of topiramate
phenytoin
Carbamezipine
Valproic acid
Most common adverse effects TOPAMAX
PSYCHOMOTOR SLOWRING
Difficulty with memory.
HYPERCHLOREMIC METABOLIC ACIDOSIS
Zonisamide
Sulfa derivative
Zonisamide metabolism ***
Half life is
• Extensively binds to erythrocytes, resulting in an eight-fold higher concentration in red blood cells (RBC) than in plasma
Plasma t1/2 = ~63 hours
Seizure meDICATION HALF LIFE ______
long
PHENYTOINC , CARBAMEZAPINE < PHENOBARBITLA
Are all enzyme inducers
LACOSAMIDE (VIMPAT)
Extremely expensive
Selectivlty enhances slow inactivation of voltage gated Na+ channels
Lacosamide Metabolism
metabolized CYP 450 enzymes
Lacosamide can cause
Can cause HB
dose dependent
Afib or aflutter
Rufinamide
Triazole derivative
Modulation of the activity of Na channel
CLINICAL USE of RUFINAMIDE (hard to treat)
Lennox-GASTAUT SYNDROME
Adverse effects of RUFINAMIDE on conduction
SHORT QT syndrome
VIGABATRIN is a
Irreversible inhibitor of GABA-T the enzyme responsible for the metabolism of the inhibitory neurotransmitter GABA
Vigabatrin side effects (3)
PERMANANT BLINDNESS
Peripheral neuropathy
Birth defects
Ezogabine (POTIGA)
Potassium channel opener enhance transmembrane potassium current mediated by the KCNQ family of ion channels
Pharmacokinetics of EZOGABINE
Metabolized by
Active metabolites?
effect on conduction?
several nonCYP
Has active meablites
PROLONG QT INTERVAL
PERAMPANEL (FYCOMPA)
First and only AMPA Glutamate Receptor antagonist
First and only AMPA Glutamate Receptor antagonist
Perampanel (Fycompa)
Non-competitive at receptor site_____
stay longer
Eslicarbazepine acetate : Protein binding is _____and excreted via _______
has a low protein binding
Via renal excretion
Felbamate: when use
SEVERE TROUBLE, LAST effort medicaiton
**Felbamate SERIOUS ADVERSE EFFECTS (2)
- Aplastic anemia
- HEPATOTOXICITY
Additional, only approved for partial seizures
PERAMPANEL
Phenytoin Dose
16-20mg/Kg of TBW
Fosphenytoin loading dose
15-20mg PE/kg for status epilepticus