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Epileptic Drugs Flashcards

1
Q

HLA-B 1502

A

predisposed people for interaction with aromatic AED’s

can be fatal, you see skin reactions known as Stevens-Johnson Syndrome or toxic epidermal necrolysis

more common in Asians

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2
Q

HLA-A 3101

A

strongly associated with carbamazepine-induced drug reaction with eosinophilia and systemic symptoms

known as “DRESS”

Seen in European and Asian patients

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3
Q

aromatic AED’s

A 
carbamazepine
oxcarbazepine
eslicarbazepine
phenytoin
lamotrigine
phenobarbital

these drugs are known to have pharmacogenomic interactions.

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4
Q

what AED’s are known inducers of CYPs, UGTs and P-glycoprotein?

A

phenobarbital
primidone
phenytoin
carbamazepine

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5
Q

which AEDs are specifically weak to moderate inducers of CYP3A4?

A

oxcarbazepine

eslicarcazepine

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6
Q

which AED is an inhibitor of CYPs and UGTs?

A

Valproate

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7
Q

What are the voltage-gated Na+ channel Inhibitors?

A

Phenytoin
Fosphenytoin
Lamotrigine
Carbamazepine

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8
Q

What’s the absorption, distribution, metabolism and excretion of phenytoin?

A

Given Oral, IV, IM

IM route is not recommended, IV route is painful

distributes to the brain, liver, muscle and fat.

Hepatic metabolism - CYP2C9 & 19, CYP3A4 with glucuronide metabolites

Zero order kinetics - this mean the half life of the drug depends on the plasma concentration

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9
Q

what patients require dose adjustments for phenytoin therapy?

A

patients with renal failure require lower maintenance doses - but not loading doses

patients with hypoalbuminemia may require lower dosing because it can decrease protein binding (freeing up drug)

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10
Q

MOA of Phenytoin

A

prolongs the inactivated (refractory) state of VG Na+ channel

this blocks the high-frequency repetitive firing of action potentials and decreases the propagation of synaptic impulses

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11
Q

Uses of phenytoin

A

Focal seizures

Generalized Tonic-Clonic Seizures

Status epilepticus

Prevention and treatment of seizures during or following neurosurgery

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12
Q

what are the adverse effects of phenytoin?

A

nausea, nystagmus, diplopia, dizziness, cognitive impairment, ataxia, tremor and sedation

peripheral neuropathy, atrophy of the cerebellum

Vitamin D and folic acid deficiency

Gingival hyperplasia, hirsuitism and coarsening of facial features

serious toxicities - skin, rash, Steven Johnson Syndrome, and toxic epidermal necrolysis, hepatitis and agranulocytosis

IV-related: hypotension, bradycardia, dysrhythmia, extravasation, purple glove syndrome

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13
Q

side effects for Phenytoin - PHENTOINS

A

P - P-450 P-Glycoprotein interactions
H - Hirsutism
E - Enlarged gums
N - Nystagmus
Y - Yellowing of skin
T - teratogenicity
O - Osteomalacia
I - interfers with folic acid absorption causing anemia
N - Neuropathies: vertigo, ataxia and headache
S - skin coarsening, skin reactions, purple glove syndrome

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14
Q

What are phenytoins effects in pregnancy?

A

increased risk of congenital malformations:

skull and facial abnormalities

microcephaly

mental retardation

underdeveloped nails of fingers and toes

Hypoprothrombinemia and hemorrhage have occurred in the
newborns - supplementation with Folic Acid and Vitamin K

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15
Q

how does phenytoin affects the thyroid function diagnostic test?

A

it can make it seem like serum levels are high because phenytoin bind TBG and displaces thyroxin

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16
Q

how is carbamazepine different from oxcarbazepine and eslicarbazepine?

A

carbamazepine is metabolized by and a strong inducer of CYP3A4

Oxcarbazepine and eslicarbazepine are weaker inducers. These are also renally excreted

Eslicarbazepine Inhibits CYP2C19

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17
Q

what is the MOA of carbamazepine?

A

it prolonged the inactive state of VG Na+ channels by binding allosterically.

this blocks sustained firing and decreases propagation of synaptic impulses

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18
Q

what are the therapeutic uses of carbamazepine and it’s related drugs?

A

focal seizures

focal seizure that evolves to generalized seizures

the non-seizure applications include Trigeminal Neuralgia and Acute Mania

Oxcarbazepine and Eslicarbamazepine are used solely for focal seizures.

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19
Q

what are the cautions or adverse effects of carbamazepine?

A

acute side effects - dizziness, sedation (high dose), ataxia, nystagmus and nausea

HLA-B1502 (Asians) and HLA-A 3101 patients have severe hypersensitivity skin reactions - SJS, TENS, hepatotoxicity (DRESS)

Syndrome of inappropriate ADH - unregulated water reabsorption causing hyponatremia and water intoxication.

tertatogenic effects — Increased risk of spina bifida, craniofacial defects, cardiovascular malformations, and hypospadias

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20
Q

lamotrigine

A

given orally with 98% bioavailability

hepatic glucuronidation which is renally excreted

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21
Q

what are the important drug and disease interactions of Lamotrigine?

A

Valproate - half life is more than doubled

Halflife is reduced in patients taking strong broad spectrum inducers - carbamazepine, phenytoin, phenobarbital and primidone

half-life is increased in patients with hepatic insufficiency

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22
Q

what are the MOA of Lamotrigine?

A

VG Na+ channel blocker with potential additional actions. Block is dependent on the use of the channel

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23
Q

What are the therapeutic uses of lamotrigine?

A

Broad spectrum - partial seizures, primary generalized seizures and generalized seizures of Lennox-Gestaut syndrome

nonseizure - bipolar disorder 1

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24
Q

what are the adverse effects of lamotrigine?

A

nausea, dizziness, tremor, diplopia, ataxia, anxiety and insomnia

Can worsen migraine headaches

series reactions are SJS, TEN and DRESS with HLA-B 1502 being the most at risk

Reduce risk by slow titration.

Even slower titration when administered with Valproate

25
lamotrigine: pregnancy effects and drug interactions
pregnancy effects in humans are not fully known yet Phenytoin, carbamazepine, and phenobarbital induce metabolism of lamotrigine Valproic acid inhibits lamotrigine’s metabolism
26
Valproic Acid - pharmacokinetic properties
Valproate is taken orally or given by IV Oddball AED because of High Protein Binding hepatic metabolism including CYP, glucuronide conjugation and mitochondrial Beta-oxidation on the short side half life that increased in patients with liver disease Valproic acid inhibits CYP2C9 and induces CYP2A6
27
Valproate MOA
VG Na+ channel block reduces VG T-type Ca+ channel currents -this limits sustained repetitive neuronal firing increases synaptic GABA: stimulating the synthesis inhibiting it's degradation inhibiting the transporter that would remove it from the synaptic cleft (GAT-1)
28
Therapeutic Uses of Valproate
Generalized tonic-clonic seizures focal seizures absence seizures status epilepticus non-seizure applications include Acute Mania, migraine prophylaxis and diabetic neuropathy
29
Valproate Adverse effects
common ones are nausea, vomiting, abdominal pain and heartburn - gradual titration of the drug helps with these sedation, dizziness, ataxia and cognitive impairment weight gain, hair loss and tremor hepatotoxicity thromcocytopenia and reduced platelet function hyperammonemia acute pancreatitis - rare increases prevalence of polycystic ovary syndrome
30
teratogenic effects of valproate
neural tube defects craniofacial defects cardiovascular malformation
31
drug interactions of Valproate
displaces plasma protein binding valproate will increase levels of Lamotrigine when these are given in unison it's important to do an extra slow titration of the Lamotrigine
32
Topiramate - MOA
Blockage of VG Na+ channels Depresses the excitatory action of AMPA Binds GABA-receptor and enhances inhibitory effect of GABA inhibits carbonic anhydrase - causes the inability to sweat and hyperthermia
33
Topiramate - therapeutic uses
focal seizures primary generalized tonic-clonic seizures lennox-gastaut syndrome non-seizure applicants include prophylaxis of migraine and cluster headaches, neuropathy and weight loss
34
Topiramate - common adverse effects
Somnolence, fatigue, dizziness, cognitive slowing, paresthesias, nervousness, and confusion Weight loss
35
Topiramate - Adverse effects due to the inhibition of carbonic anhydrase
oligohydrosis leading to hypothermia increased risk of kidney stone formation metabolic acidosis (by decreasing serum bicarbonate) acute myopia with secondary angle-closure glaucoma
36
topiramate - pregnancy and drug interaction
May cause fetal harm: oral clefts; hypospadias; other congenital anomalies use of valproate and topiramate together can cause hyperammonemia which could eventually lead to encephalopathy other CNS depressants may enhance it's effets
37
Felbamate - MOA
blocks NMDA glutamate receptor - the block depends on the use of the receptor potentiation of GABA mediated inhibition
38
felbamate - therapeutic uses
should really be the last line - refractory uses because of the serious side effects focal seizures Lennox-Gestaut syndrome Informed consent must be obtained
39
Felbamate - adverse effects, contraindications and common side effects
adverse effects are very serious - aplastic anemia and serious hepatitis contraindiced in patients with blood disorders or liver disease common side effects are nausea, vomiting, headache, dizziness, somnolence, and insomnia
40
Gabapentin - PK and MOA
gabapenoids - gabapentin and pregabalin Drug is taken in by L-type amino transporters The MOA is by blocking the alpha2gamma subunit of VG Ca+
41
Ganapentin - therapeutic uses
adjunct for treatment of focal seizures neuropathic pain and many other off-label uses
42
adverse effects of gabapentin
minor - sedation, dizziness, weight gain and peripheral edema no human known adverse pregnancy effects - put on pregnancy registry
43
Levetiracetam - MOA and PK
Drug binding to SV2A appears to reduce the synaptic release of glutamate and GABA given IV with 100% bioavail and excreted renally - 2x daily dosing
44
Levetiracetam - Therapeutic uses
adjunct therapy for focal seizures seizures Primary generalized tonic-clonic myoclonic seizures
45
Levetiracetam - adverse effects
fatigue and irritability weakness and dizziness psychotic symptoms there is low potential for metabolic drug interactions
46
ethosuximide - PK and Therapeutic Uses
Given orally metabolized by CYP3A4 but excreted renally long half life - 50h in adults and 30h in children used for Absence seizures
47
ethosuximide - MOA
reduces low threshold Ca2+ channel currents in thalamic neurons supresses spike and wave EEG pattern seen in absence seizures and raises the threshold for seizure event
48
ethosuximide - Adverse Effects
nausea and vomiting somnolence, sleep disturbance and hyperactivity
49
phenobarbital - PK and MOA
PK - Oral and IV with 50% protein binding. Metabolized by CYP2C9 and some renal excretion Very long half life - 1.5 to 5 days MOA - bind allosteric sites of alpha and beta subunits of GABA - receptor prolonging the duration of Cl- channel closure leading to a higher influx of Cl- causing a decreased in excitability (hyper-polarization)
50
phenobarbital - Therapeutic uses
focal seizures generalized tonic-clonic seizures status epileptics
51
phenobarbital - adverse effects
sedation, depression of mood, cognitive impairment, hyperactivity, agitation and porphyria (in susceptible pops) Rash, hepatotoxicity and bone marrow toxicity can cause respiratory depression when used with Benzos hypotension fetal risks
52
Benzodiazepine
diazepam lorazepam clonazepam
53
Benzodiazepine - MOA
binds to allosteric site on alpha and beta subunits of GABA receptor causing increased frequency of opening of Cl- channels
54
diazepam
benzo with rapid onset and short action action is short because of a rapid redistribution
55
clonazepam
oral with slower onset but longer anti-seizure activity metabolized by CYP3A4 can be used alone with adjunct for Lennox-Gastaut syndrome, petit mal variant. Akinetic and myoclonic seizures
56
nonseizure uses of Benzo's
Anxiety; panic disorder; alcohol withdrawal; muscle relaxant (esp diazepam); sedative-hypnotic; preop sedation, anxiolysis, and amnesia; induction of anesthesia (balanced anesthesia); sedation for mechanically ventilated patients
57
Adverse Effects of Benzos
Oral/Rectal - sedation, depression, incoordination and behavioral disturbances parenteral - Acute hypertension, muscle weakness, respiratory depression and cardiac arrest
58
Benzo - pregnant patient
teratogenic floppy baby syndrome with withdrawl symptoms

Pharmacology (23 decks)

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