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Pharm III Unit I > 2 Anticonvulsants > Flashcards

2 Anticonvulsants Flashcards

1
Q

What are seizures exactly?

A

Abnormal discharges of electrical activity in cerebral neurons

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2
Q

Neurological disorder characterized by recurrent seizures

A

Epilepsy

1% of the world’s pop has it

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3
Q

Seizures typically originate in what part of the brain?

A

Cerebral cortex

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4
Q

What causes seizures?

A 
Can be...
Neurological disease
Head trauma
Infection
Tumors
Drugs
High fevers

About 50% have unknown origins

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5
Q

What are the different classifications of seizure?

A

Partial (originates in one are of the brain)
• Simple
• Complex
• Partial with 2˚ general

Generalized (involves whole brain)
• Absence
• Tonic-clonic
• Myoclonic
• Atonic
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6
Q

Name that seizure!

Focal
Brief (20-90 sec)
Grimacing, focal clinic jerking of an extremity
No loss of consciousness

A

Simple partial

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7
Q

Name that seizure!

Focal
Longer (<2 min)
Altered or loss of consciousness
Temporal lobe
Automatic movements
A

Complex partial

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8
Q

Name that seizure!

Starts focal —> general
Loss of consciousness
Muscle contractions alternating with relaxation

A

Partial with secondary generalized tonic-clonic

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9
Q

Name that seizure!

Arise from reciprocal firing of thalamus and cortex

A

Generalized seizures

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10
Q

Name that seizure!

Initial tonic rigidity (15-30s)
Subsequent tremor
Eventually clonic jerking (60-120s)
LOC
Patient stuporous and confused
A

Tonic-clonic (grand mal)

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11
Q

Name that seizure!

Sudden onset
Brief (10-30s)
Loss of awareness but not consciousness
May be some mild clonic movements

A

Absence (petit mal)

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12
Q

Name that seizure!

Brief spasm or rigidity
Often secondary to other seizure disorders

A

Myoclonic

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13
Q

Name that seizure!

Sudden loss of postural tone
Patient can fall done

A

Atonic

No drugs - they have to wear a helmet

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14
Q

What are the two targets for anticonvulsant medications?

A

Increase GABA activity (b/c blockade of GABA receptors causes seizures)

Decrease excitatory glutamate activity (b/c activation of glutamate NMDA receptors can lead to seizures)

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15
Q

Mechanisms for increasing GABA activity for the treatment of seizures

A

Block GABA reuptake (Tiagabine)

Inhibit GABA metabolism (Vigabatrin)

Stimulate GABA-a receptors (Benzos and barbs)

Bind to synaptic vesicular protein SV2A (Levetiracetam)

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16
Q

Mechanisms for decreasing glutamate activity for the treatment of seizures

A

Common targets: Voltage-gated Na+ and Ca2+ channels (Phenytoin, ethosuximide)

Other targets: SV2A, K+ channels, NMDA and AMPA receptors

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17
Q

To treat absence seizures, drugs need to target…

A

Ca2+ channels

Ethosuximide is really the only drug that does

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18
Q

How does inhibition of Na+ channels work to treat seizures?

A

Voltage gated Na+ channels become inactive after each firing

Inactivation state is prolonged so the action potential does not fire as rapidly

Targets rapidly firing neurons

No effect on normal neurons

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19
Q

Where do drugs that inhibit Na+ channels to inhibit glutamate activity bind?

A

INTRAcellularly (have to cross the membrane)

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20
Q

What are the general principles to remember for anticonvulsant therapy?

A

Most drugs will stop seizures without side effects - 50% of patients

Monitor plasma drug levels and use SINGLE DRUG if possible

Common side effects - GI, CNS disturbances
• Teratogenic
• Hypersensitivity (Stevens-Johnson syndrome)

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21
Q

Most anticonvulsant drugs are metabolized by CYP450s but these three INDUCE CYP450s

A

Phenytoin

Carbamazepine

Phenobarbital

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22
Q

What is the main difference between Phenytoin (Dilantin) and Fosphenytoin (Cerebyx)?

A

Phenytoin is not injectable (not water soluble)

Fosphenytoin is injectable

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23
Q

Uses for Phenytoin and Fosphenytoin

A

Partial seizures and generalized tonic-clonic seizures

NOT effective for absence seizures

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24
Q

Phenytoin/Fosphenytoin MOA

A

Prolongs the inactivation of Na+ channels to decrease glutamate activity

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25
Q

Phenytoin and Fosphenytoin are elimated by ______ kinetics at low doses but ______ at therapeutic and high doses

A

1st order

Zero order

Because of this, small changes in dose/elimination can cause BIG changes in plasma levels

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26
Q

Phenytoin is likely to have interactions with…

A

Drugs that alter CYP450s

It is metabolized by, induces, AND inhibitors CYP450s!

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27
Q

Side effects of phenytoin

A

Nystagmus, diplopia, ataxia, sedation

GINGIVAL HYPERPLASIA***

Long term:
• Coarsening of facial features
• Mild peripheral neuropathy
• Abnormal vitamin D metabolism

Skin rash - d/c!!! (Risk of SJS)***

Pregnancy Category D

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28
Q

What are the primary uses for Carbamazepine (Tegretol)

A

DRUG OF CHOICE for PARTIAL seizures**

Generalized tonic-clonic seizures

Bipolar disorder

TRIGEMINAL NEURALGIA

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29
Q

Carbamazepine (Tegretol) increases metabolism of …

A

Multiple anticonvulsants

Haloperidol***

Oral contraceptives***

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30
Q

Metabolism of Carbamazepine (Tegretol) is increased by _________ and inhibited by __________

A

Phenobarbital, Phenytoin

Cimetidine, fluoxetine, and VALPROIC ACID

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31
Q

Side effects of Carbamazepine (Tegretol)

A

Diplopia, ataxia, GI upset, drowsiness

Aplastic anemia and agranulocytosis

Highest potential for STEVENS JOHNSON SYNDROME of the anticonvulsants

Pregnancy Category D

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32
Q

Patients with _________ are more likely to develop Stevens Johnson Syndrome when taking Carbamazepine

A

HLA-B 1502

Genetic screening is REQUIRED prior to prescribing

33
Q

MOA for Lamotrigine (Lamictal)

A

Inactivation of Na+ channels; decreases glutamate activity

May also inhibit Ca2+ channels

34
Q

Uses for Lamotrigine (Lamictal)

A

Partial seizures**

May be effective against myoclonic and absence seizures in children

Bipolar disorder

35
Q

What pharmacokinetic details do we need to know about Lamotrigine (Lamictal)?

A

Inducers of CYP450s (phenytoin, carbamazepine, phenobarbital) will increase metabolism

Half-life double by valproic acid

36
Q

Side effects of Lamotrigine (Lamictal)

A

CNS - dizziness, HA, diplopia, ataxia, somnolence

GI - nausea and vomiting

Skin rash and Stevens-Johnson Syndrome

Pregnancy Category C (better than the others but still not good)

37
Q

How is Topiramate (Topamax) used?

A

Partial and generalized tonic-clonic seizures

May also be effective for absence seizures

Migraine prevention***

38
Q

MOA for Topiramate (Topamax)

A

Blocks Na+ channels and decreases glutamate activity

Also has some activity at Ca2+ channels

Potentialities GABA receptors and inhibits glutamate receptor

May inihibit spread of seizures

39
Q

Topiramate (Topamax) may increase metabolism of ________.

A

Contraceptives

40
Q

Side effects of Topiramate (Topamax)

A

Dizziness, sedation, nervousness, confusion

ACUTE MYOPIA/GLAUCOMA

41
Q

Uses for Levetiracetam (Keppra)

A

Partial, myoclonic, and tonic-clonic seizures

42
Q

MOA for Levetiracetam (Keppra)

A

Binds synaptic vesicular protein (SV2A) —> decreased glutamate and increased GABA release

43
Q

Pharmacokinetics for Levetiracetam (Keppra)

A

Oral absorption is rapid - peak blood concentrations in 1-2h

1/2 life of 6-8h, longer in elderly

44
Q

Side effects of Levetiracetam (Keppra)

A

Dizziness, somnolence, ataxia, and asthenia

45
Q

__________ has minimal drug interactions so is a good option for multidrug therapy

A

Levetiracetam (Keppra)

46
Q

MOA for Phenobarbital (Luminal)

A

Prolongs opening of chloride channel at GABA receptor —> alters Na+ and Ca2+ conductance at high concentrations

47
Q

Uses for phenobarbital (luminal)

A

Partial seizures

Generalized tonic-clonic seizures

Potential for abuse those so use with caution

48
Q

Phenobarbital _______ CYP450s

A

Induces —> increased metabolism of phenytoin and carbamazepine

49
Q

Uses for Gabapentin (Neurontin)

A

ADJUNCT for partial and generalized tonic-clonic seizures

Neuropathic pain**

Bipolar disorder (off label)

50
Q

MOA for Gabapentin (Neurontin)

A

GABA analog***

May augment GABA release

51
Q

Pharmacokinetics of Gabapentin (Neurontin)

A

1st order elimination by the kidneys

Short half-life, taken 3x/day

52
Q

Side effects of Gabapentin

A

Sleepiness, dizziness, ataxia, fatigue, tremor, H/A

Pregnancy Cat C

53
Q

_______ has negligible drug interactions, so it’s a good 2nd drug for multidrug therapy

A

Gabapentin

54
Q

What is Pregabalin (Lyrica) and how is it used?

A

GABA analog - structurally related to GABA

Binds to alpha-2-delta subunit of voltage-gated Ca2+ channels inhibiting excitatory neurotransmitter release

Used for generalized anxiety disorder***

Other uses: neuropathic pain, fibromyalgia, post-op pain

55
Q

Side effects of Pregabalin (Lyrica)

A

Peripheral edema, dizziness, fatigue, weight gain, xerostomia***, ataxia, blurred vision, GI disturbances

TERATOGENIC

56
Q

Adjunct treatment for partial seizures that works by inhibiting reuptake of GABA (GAT-1) to enhance GABA activity

A

Tiagabine (Gabitril)

57
Q

Side effects of Tiagabine (Gabitril)

A

Nervousness, difficulty concentrating, depression

Dizziness, tremor, rash (rare but d/c if happens)

Pregnancy Cat C

58
Q

How is Vigabatrin (Sabril) used?

A

Refractory complex partial seizures

Infantile spasm (West’s syndrome)

59
Q

MOA for Vigabatrin (Sabril)

A

IRREVERSIBLY inhibits GABA transaminase (GABA-T) to decrease GABA metabolism and enhance activity

Short half-life but b/c of MOA drug effects are prolonged and do not correlate with plasma levels

60
Q

Side effects of Vigabatrin (Sabril)

A

Visual field problems and retinal damage**

Agitation, confusion

61
Q

Drug of choice for absence seizures

A

Ethosuximide (Zarontin)

62
Q

MOA for Ethosuximide (Zarontin)

A

Inhibits low-threshold (T-type) Ca2+ channels

Inhibits ‘pacemaker’ for rhythmic cortical diamanté

63
Q

Side effects of Ethosuximide (Zarontin)

A

GI irritation, lethargy, fatigue, HA, dizziness

HICCUPS**

Stevens Johnson Syndrome (very rare)

Metabolism is inhibited by VALPROIC ACID

64
Q

Uses for Valproic Acid (Depakene)

A

Absence AND general tonic-clonic seizures (MIXED seizures)

Bipolar disorder

Prophylaxis of migraine

65
Q

MOA for Valproic Acid (Depakene)

A

Blocks Ca2+ channels and Na+ channels

May enhance GABA activity

66
Q

Pharmacokinetics for Valproic Acid (Depakene)

A

Absorption is prolonged by food

1/2life of 9-18h

INHIBITS ITS OWN METABOLISM at low doses

67
Q

Valproic acid inhibits metabolism of …

A

Phenytoin

Phenobarbital

Carbamazepine

68
Q

Side effects of Valproic Acid

A

Nausea, abdominal pain, heartburn, weight gain, sedation, tremor, alopecia

HEPATOTOXICITY - monitoring of liver function is REQUIRED

Pregnancy Cat D

69
Q

How is Clonazepam (Klonopin) used as an anticonvulsant?

A

Absence seizures, myoclonic seizures, and infantile spasms (West Syndrome)

70
Q

MOA for Clonazepam (Klonopin)

A

It’s a Benzo

Stimulates GABA receptor and enhances GABAergic inhibition

71
Q

Side effects of Clonazepam (Klonopin)

A

Sedating

Tolerance to anti-seizure effect

Pregnancy Cat D

72
Q

Drug of choice for Status Epilepticus

A

Diazepam (Valium) and Lorazepam (Ativan)

Both are benzos

73
Q

MOA for benzos

A

Stimulates GABA channel

74
Q

All the anticonvulsants have some degree of teratogenicity but valproic acid increases the risk of …

A

Spina Bifida

75
Q

Withdrawal from anticonvulsants can lead to…

A

Rebound increase in seizure activity

76
Q

Overdose of anticonvulsants

A

CNS depression but rarely lethal

Need high drug plasma levels

Respiratory depression most common effect of large overdose

Do NOT treat with CNS stimulants

77
Q

Which anticonvulsants increase the risk for Stevens Johnson Syndrome?

A

Drugs that block Na+ channels - Phenytoin, Lamotrigine, CARBAMEZAPINE, Valproate

Patients should be screened for HLA-B 1502

78
Q

Failure rate of contraceptives is ____ for patients on anticonvulsants versus _____ in the general population

A

3.1% v 0.7%

79
Q

Birth defects are ____ as likely when on anticonvulsants as opposed to general population rate

A

2x

Congenital heart defects and neural tube defects are most common

Pharm III Unit I (9 decks)

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