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Pharm > Lecture 15: Drugs used to Treat Seizure Disorders > Flashcards

Lecture 15: Drugs used to Treat Seizure Disorders Flashcards

1
Q

What are Seizures?

A

A transient alteration of behavior due to abnormally excessive and synchronous neuronal activity in the brain

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2
Q

What is Epilepsy?

A

A disorder of brain function characterized by the periodic and unpredictable occurrence of seizures

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3
Q

What does it mean for epilepsy to be symptomatic?

A

Occur due to a known even such as head trauma or cancer

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4
Q

What does it mean for epilepsy to be asymptomatic?

A

Generally due to poorly defined genetic factors but don’t really know the cause of the seizures

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5
Q

Do seizures need to be provoked by something?

A

Seizures can be provoked or unprovoked

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6
Q

With what synchronicity do neurons usually fire in the brain?

A

They usually fire asynchronously in normal conditions

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7
Q

What is the spread of electrical activity maintained by?

A

Changes in membrane potential following depolarization (refractory period) and surround inhibition

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8
Q

How is electrical activity insulated in the brain?

A
  • By the refractory period of an action potential

* By surround inhibition

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9
Q

What is Surround Inhibition?

A

The physiological mechanism that focuses neuronal activity in the central nervous system

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10
Q

What are primary afferents?

A

Neurons that innervate the skin and any surface of our body

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11
Q

What happens if the receptive field of a neuron is stimulated?

A

It will produce more action potential than those on the periphery of the receptive field

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12
Q

What happens if the edge of a neuron’s receptive field is stimulated?

A

It will not produce as many action potentials of those that are stimulated in the center of the receptive field

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13
Q

What happens when a neuron in the receptive field synapses with the interneuron?

A

The interneuron creates action potentials but also activates GABAergic neurons which inhibits the neighboring neurons to quiet their neuronal activity

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14
Q

How does surround inhibition work?

A

The neuron that is stimulated inhibits action potentials in the surrounding neurons but activating GABAergic neurons

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15
Q

What are the three steps in seizures?

A
  • Initiation
  • Propagation
  • Termination
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16
Q

What two events is seizure initiation characterized by?

A
  • High frequency bursts of action potentials

* Hyper synchronization of neuronal population

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17
Q

Which receptors does high frequency stimulation recruit?

A

NMDA receptors

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18
Q

What flows through NMDA receptors?

A

Calcium

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19
Q

What are the two main classes of glutamate receptors?

A
  • AMPA receptors

* NMDA receptors

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20
Q

What receptors drive the excitatory effect of glutamate initially?

A

AMPA receptors

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21
Q

How do AMPA receptors work?

A

Glutamate binds to the AMPA receptor causing it to open and sodium can flow into the cell causing membrane depolarization

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22
Q

Why are NMDA receptors usually inactive?

A

Because they have a magnesium block in them that blocks the flow of sodium even when glutamate binds to them

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23
Q

When are NMDA active?

A

When many AMPA receptors are active allow the magnesium block to dissociate

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24
Q

What ions are NMDA receptors permeable to?

A

Calcium and sodium

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25
Q

What is the sustained neuronal depolarization in seizures driven by?

A

Calcium influx through NMDA receptors

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26
Q

What is the propagation of bursting activity in the brain normally prevented by?

A

Hyperpolarization and surround inhibition

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27
Q

How can the barriers of surround inhibition and hyperpolarization be overcame?

A
  • Increasing extracellular potassium
  • Accumulation of calcium
  • Activation of the NMDA receptor
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28
Q

What does increasing extracellular potassium do?

A

Blunts the hyperpolarizing outward potassium currents

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29
Q

What does increased accumulation of calcium do?

A

In the presynaptic terminals leads to enhanced neurotransmitter release

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30
Q

What does activation of the NMDA receptor do?

A

Causes more calcium influx and neuronal activation

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31
Q

What happens if the barriers of hyperpolarization and surround inhibition are overacame?

A

Then seizure activity is propagated through the brain

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32
Q

How do seizures generally resolve?

A

Spontaneously

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33
Q

The do the mechanisms that terminate a seizure involve?

A
  • loss of ionic gradients
  • depletion of ATP
  • depletion of neurotransmitters (e.g. glutamate)
  • activation of inhibitory circuits (GABA)
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34
Q

What is Status Epilepticus?

A

A seizure lasting longer than 5 minutes of having more than 1 seizure within a 5 minute period. This is life threatening

35
Q

What is a postictal period?

A

The 5-30 minutes after a seizure that is characterized by drowsiness, confusion, depression/anxiety and sometime psychosis

36
Q

Why does the Postictal period occur?

A

Because of abnormal electrical activity in the brain resetting

37
Q

What do the different classification of seizures depend?

A
  • Where in the brain they initiate

* How widely they propagate

38
Q

What are the three types of seizure classes?

A
  • Focal seizures
  • Generalized seizures
  • Nonconvulsive (absence) seizures
39
Q

What do the diverse manifestations of Focal seizures depend on?

A

Where in the brain it originates

40
Q

What is the difference between simple and complex Focal seizures?

A

Simple - Retain consciousness

Complex - Loss of consciousness

41
Q

What is jerking activity like in Focal seizures?

A

Jerking activity may start in a specific muscle group and spread to surround muscle groups

42
Q

What are Automatisms that are seen in Focal seizures?

A

Unusual activities that are not consciously created like smacking the lips

43
Q

What is a Focal Seizure?

A

Abnormal electrical activity that occurs in a very precise part of the brain and doesn’t spread very far

44
Q

What does the different behavioral manifestation of a Focal seizure indicate?

A

Where in the brain the seizure is occuring

45
Q

What is Jacksonian March?

A

In focal seizures where the jerking activity may start in a certain muscle and spread to surrounding muscle groups

46
Q

What are Generalized seizures?

A

Abnormal electrical activity that starts in one precise part of the brain but then migrates or propagates throughout the entire brain

47
Q

What are the two types of Generalized Seizures?

A

Tonic-clonic and Myoclonic

48
Q

How do generalized seizures effect conciousness?

A

They generally involve loss of consciousness and occur without warning

49
Q

What are Tonic-clonic generalized seizures?

A

Sustained contractions (tonic) of muscles throughout the body followed by periods of alternating muscle contraction and relaxation (clonic)

50
Q

What are Myoclonic generalized seizures?

A

A brief (~1s) shock like contraction of muscles that may be localized or generalized

51
Q

What are the two types of Non-convulsive seizures?

A

Absence and atonic seizures

52
Q

What are Absence seizures characterized by?

A

An abrupt onset of impaired consciousness

53
Q

What are Atonic seizures characterized by?

A

A sudden loss of muscle strength

54
Q

How is consciousness affected in atonic seizures?

A

Usually consciousness is maintained but a person may fall down

55
Q

What are anti seizure drugs used for?

A

To prevent the occurrence of seizures in people with epilepsy

56
Q

When are anti seizure drugs used to treat people without epilepsy?

A

When people have acute illnesses such as meningitis that may cause seizures

57
Q

Can epilepsy be cured or prevented?

A

No

58
Q

What do anti seizure drugs generally do?

A
  • Enhance inhibitory (GABAergic) neurotransmission

* Diminish excitatory (glutamatergic) neurotransmission

59
Q

How do antiseizure drugs enhance GABA or decrease glutamate?

A
  • blocking ion conductance (Na, Ca and K)
  • blocking neurotransmitter release
  • inhibiting/activation the postsynaptic membrane
60
Q

How do seizure medication effect GABA?

A

The bind to the GABAa receptor on the postsynaptic membrane

61
Q

What kind of receptor is the GABAa receptor?

A

A ligand gated ion channel that allows chloride to flow into the cell hyperpolarize the membrane

62
Q

What are the two antiseizure drugs that target the GABA system?

A
  • Benzodiazepines

* Barbiturates

63
Q

What do Benzodiazepines and Barbiturates do?

A

They enhance the activity of GABA by binding to an allosteric site

64
Q

What is the difference between Benzos and Barbiturates at the GABA receptor?

A

Benzos have no effect on the GABA receptor in the absence of GABA while barbiturates can act as GABA agonists at higher concentrations

65
Q

What kind of ligands are Benzos and barbiturates to GABAa receptors?

A

They are positive allosteric modulators

66
Q

What is the difference in frequency of the GABAa channels that Benzodiazepines and Barbiturates act?

A
  • Benzos increase frequency at which GABAa receptor opens

* Barbiturates increase the duration at which the GABAa receptor is open

67
Q

What is the difference between Benzodiazepines and Barbiturates affect efficacy and potency?

A

Benzodiazepines increase Potency

Barbiturates increase Efficacy

68
Q

Why is the risk of overdose higher for barbiturates?

A

Because it directly gates the GABA receptor

69
Q

When is there an added risk when taking Benzodiazepines or Barbiturates?

A

When taken with other CNS depressants like alcohol or opioids

70
Q

What does Vigabatrin do?

A

Inhibits GABA aminotransaminase (GABA-T) that is involved in the degradation of GABA

71
Q

What does Tiagabine do?

A

Inhibits the GABA transporter (GAT-1 located in neurons and glia) which prolongs the action of the neurotransmitter

72
Q

What does Carbamazepine do?

A

Blocks voltage gated sodium channels

73
Q

How does Carbamazepine block voltage gated sodium channels?

A

By causing a conformational change of the inactivation gate after entering the cell

74
Q

What is the Phobicity of Carbamazepine?

A

It is lipophilic so it enters the the cell

75
Q

What is the rate of sodium channel blockers like carbamazepine dependant on?

A

The frequency of cell firing. A cell that fires more is blocked more

76
Q

What does Gabapentin look like?

A

A GABA molecule covalently bound to a lipophilic cyclohexane ring

77
Q

What does Gabapentin do?

A

Inhibits voltage gated calcium channels by binding to the alpha2delta subunit preventing glutamate neurotransmitter release

78
Q

What kind of drug a Perampanel?

A

It is a non-competitive antagonist at the AMPA receptor

79
Q

What does Perampanel do?

A

It blocks AMPA receptors so it blocks action potentials

80
Q

What are the side effects of Perampanel?

A
  • Behavioral changes
  • Mood disorders
  • Suicidal/homicidal ideation
81
Q

Why is consideration of pharmacokinetic properties important for seizure medications?

A

Because the drugs are taken for long periods the need to prevent toxicity

82
Q

What is the extraction ratio of anti-seizure drugs?

A

They have a low extraction ratio (can be long acting)

83
Q

Why are antiseizure drugs very lipophilic?

A

Because they need to cross the BBB

Pharm (31 decks)

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