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Pharm > Lecture 8: OTC Allergy and Insomnia > Flashcards

Lecture 8: OTC Allergy and Insomnia Flashcards

1
Q

What is the difference between first generation and second generation antihistamines?

A

First generation has an impact on wakefulness, not targeted toward allergy efficacy

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2
Q

What are allergies?

A

A hypersensitivity of the immune system to typically harmless substances in the environment

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3
Q

What can allergies include?

A
  • Hay fever
  • Food allergies
  • Atopic dermatitis
  • Allergic asthma
  • Anaphylaxis
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4
Q

What are the symptoms of allergies?

A
  • Red eyes
  • Itchy rash
  • Sneezing
  • Runny nose
  • Shortness of breath of swelling
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5
Q

What is Hay fever?

A

A form of allergic rhinitis

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6
Q

What is Rhinitus?

A

A reaction that occurs in the upper respiratory tract that leads to nasal congestion, runny nose, and sneezing

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7
Q

Which antibodies do the anaphylactic reaction involve?

A

Immunoglobulin E antibodies (IgE)

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8
Q

What causes anaphylaxis?

A
  • B cells react inappropriately to an allergen to produce IgE antibodies against the allergen
  • Antibodies bind to a receptor on mast cells or basophils
  • Subsequent exposure to the allergen triggers the release of inflammatory chemical such as histamine
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9
Q

What is a Type One allergic reaction?

A

Anaphylaxis

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10
Q

What are OTCs more geared towards?

A

The type two, three and four hypersensitivity reactions that are slightly more delayed in their onset

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11
Q

What kind of receptors are Histamine receptors?

A

G protein coupled receptors

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12
Q

What are the four classes of Histamine receptors?

A

H1
H2
H3
H4

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13
Q

What do H1 receptors play a role in?

A

The allergic response

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14
Q

Where are H1 receptors locasted?

A
  • Smooth muscle
  • Vascular endothelial cells
  • In the heart
  • In the CNS
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15
Q

What does activation of H1 receptors do?

A
  • Increases vascular permeability
  • Vasodilation
  • Stimulation of sensory neurons producing cough
  • Smooth muscle contraction of the bronchi
  • Eosinophilic chemotaxis (eosinophils migrating to tissues)
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16
Q

What directly underlies histamines ability to cause vasodilation?

A

H1 receptors on vascular endothelial cells

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17
Q

Where in the brain are histamine receptors expressed with high density?

A

In regions involved in arousal and waking (thalamus, cortex and noradrenergic, serotonergic, and dopaminergic nuclei)

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18
Q

What is histamine an important neurotransmitter in?

A

The wake-promoting system

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19
Q

Which neurotransmitters promote sleep?

A
  • GABA

* Galanin

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20
Q

What are the wake promoting neurotransmitters?

A
  • Histamine
  • Serotonin
  • Norepinephrine
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21
Q

Which part of the brain is associated with wake promoting?

A

The Thalamus

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22
Q

Why do many antihistamine drugs have an effect on alertness?

A

Because histamine in the CNS drives wakefulness

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23
Q

What is the first generation antihistamine?

A

Diphenhydramine

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24
Q

What kind of effector mechanism does Diphenhydramine have?

A

It is an inverse agonist at the H1 receptor

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25
Q

Which receptor does Diphenhydramine target?

A

The H1 receptors

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26
Q

What does Diphenhydramine do?

A

It blocks the effects of histamine in blood vessels and smooth muscle cells reducing allergic reaction symptoms

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27
Q

How does Diphenhydramine affect the brain?

A
  • It crosses the blood-brain-barrier and inversely agonizes the H1 receptors in the CNS resulting in drowsiness
  • Suppresses the medullary cough center
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28
Q

What is an inverse agonsit?

A

A drug that binds to the same receptor as an agonist but induces a pharmacological response opposite to that of the agonist

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29
Q

What are the effects of a neutral antagonist?

A

A neutral antagonist has no activity in the absence of an antagonist or inverse agonist, but can block that activity of either

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30
Q

Which G receptor pathway does histamine induce?

A

The Gq pathway

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31
Q

What is Diphenhydramine marketed as?

A
  • OTC allergy drug

* OTC sleep aid

32
Q

In addition to their activity at the H1 receptors, what do first gen antihistamines bind to?

A

Other receptors

33
Q

What can the binding of first gen antihistamines do?

A

Contribute to off-target side effects

34
Q

What does the inhibitory constant (Ki) describe?

A

How well an antagonist or inverse agonist binds to a receptor (affinity)

35
Q

How is Ki measured?

A

With fluorescently labeled competitive binding assays. A receptor bound to or expressed by a bunch of cells or the receptor itself bound to a plate and add a fluorescently labelled ligand with a known binding efficiency and saturate those receptors with a ligand. Then introduce increasing concentrations of the chemical of interest. As the conc. increases, you’d essentially wash away the original ligan until none of it is bound. So there is a decreasing level of fluorescence. The Ki is determined when 50% of the fluorescence disappeared

36
Q

What is the Ki in numbers?

A

The concentration of the drug that displaces 50% of the labeled ligand

37
Q

What does a Low Ki mean?

A

That the drug has a high affinity

38
Q

What is the cause of virtually all unwanted side affects?

A

Drugs binding to different receptors

39
Q

What is required for all drug effects?

A

Ligand receptor interactions

40
Q

Which receptors do first generation antihistamines (diphenhydramine) bind with high affinity to?

A

Muscarinic cholinergic receptors

41
Q

What is meant by first generation antihistamine (diphenhydramine) bind with high affinity to muscarinic cholinergic receptors?

A

They have anticholinergic effects

42
Q

What side effects can first gen antihistamine (diphenhydramine) have when binding to muscarinic cholinergic receptors?

A
  • Dry mouth
  • Constipation
  • Confusion
43
Q

Other than H1 receptors, which type of receptors do first gen histamines bind to?

A

Muscarinic cholinergic receptors

44
Q

Why does diphenhydramine usually bind H1 receptors at its recommended dosage?

A

Because it has high affinity for H1 receptors

45
Q

What is pKi?

A

The negative log of Ki

46
Q

Why is only H1 targeted under normal circumstances with first gen antihistamines?

A

Because the amount of diphenhydramine administered is controlled and it doesn’t reach high enough concentrations to start producing off target effects

47
Q

What tolerance of diphenhydramine develops?

A

Tolerance to the sedative effects

48
Q

How does the use of sedative antihistamine affect sleep?

A

They decrease the quality of sleep (less time in REM, more time in light sleep) so less restorative

49
Q

What can long term use of sedative diphenhydramine be associated with and why?

A

Dementia and Alzheimer’s due to anticholinergic effects

50
Q

What is the breakdown of cholinergic pathways in the brain linked to?

A

Cholinergic neuron death, alzheimer’s and dementia

51
Q

What is Tolerance?

A

Needing more drug to get the same effect

52
Q

What are the second gen antihistamines?

A
  • Loratadine
  • Cetirizine
  • Fexofenadine
53
Q

What is the difference between first and second gen antiistamines?

A

Second gen antihistamines have higher selectively for the H1 receptors

54
Q

Why do second gen antihistamines lack the sedative (drowsy) effects?

A

Because they have poor BBB permeability

55
Q

Why do second gen antihistamines need fewer doses?

A

Because the have a longer duration of action

56
Q

Why do second gen antihistamines have much higher selectivity for H1s?

A

Because they have none of the same off target binding

57
Q

What are the improvements that second gen drugs have?

A
  • They are highly H1 selective
  • There is virtually no binding to cholinergic and serotonergic receptors
  • Limited BBB barrier crossing
  • Not eliminated as quickly
58
Q

What does Cetirizine do at H1 receptors?

A

Cetirizine is an H1 receptor antagonist

59
Q

Why does Cetirizine produce minimal sedation effects?

A

Because it has poor BBB permeability

60
Q

What is the duration of action of Cetirizine?

A

Around 24 hours

61
Q

What does Loratadine do at a receptor?

A

It is an inverse agonist at the H1 receptor

62
Q

What is Loratadine usually bound to?

A

Plasma proteins (albumin)

63
Q

What is the activity of Bound proteins?

A

Bound proteins/drugs are not active

64
Q

What kind of drugs cannot exert pharmacological effects?

A

Protein bound drugs

65
Q

What must a drug that is bound need to do in order to exert pharmacologic effects?

A

They must become free drug

66
Q

What can free drug do?

A

Leave the blood and enter the tissue and bind its therapeutic target

67
Q

What is the form of drug that is available for clearance and elimination?

A

Free drug

68
Q

What will extend the duration of action?

A

A drug being highly protein bound

69
Q

What happens when Loratadine is given orally?

A

First pass metabolism converts it into desloratidine

70
Q

What does Desloratadine do in comparison to Loratadine?

A

Carries most of the anti-histamine effects (therefore is a prodrug)

71
Q

Because Loratadine undergoes first pass metabolism what is it know as?

A

A prodrug

72
Q

What is the difference in half life of Loratadine and Desloratadine?

A

Desloratadine has a half life of 27 hours and Loratadine has a half life of 8 hours

73
Q

What carries most of the antihistamine effects, Loratadine or Desloratadine?

A

Desloratadine

74
Q

What are Prodrugs?

A

Drugs that must be converted into their active form via liver metabolism

75
Q

How does Loratadine work in terms of the BBB?

A

Loratadine has poor penetration of the BBB so it does not have sedative effects

76
Q

What kinds of enzymes does the liver express?

A

CYP enzymes

77
Q

Which binds plasma proteins Desloratadine or Loratadine?

A

Desloratadine does not bind to plasma proteins but Loratadine does which is why Desloratadine distributes quicker

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