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Anti-histamines Flashcards

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1
Q

What are autacoids?

A

biological factors which act like local hormones, have a brief duration, and act near the site of synthesis. The word autacoids comes from the Greek “Autos” (self) and “Acos” (relief, i.e. drug).

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2
Q

What is the triple response of Lewis?

A
  • Red spot (capillary dilation)
  • Flare (stimulate nerve to dilate)
  • Wheal (increased capillary permeability)
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3
Q

What is histamine (what is it made from, and how is it different)?

A

Histidine without its carboxyl group

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4
Q

What is the enzyme that converts histidine to histamine?

A

Histidine decarboxylase

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5
Q

What is the use of histamine?

A

Plays a central role in immediate hypersensitivity reaction

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6
Q

What happens to histamine when it is released into tissues and blood?

A

Inactivated

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7
Q

What are the cells that contain histamine? (3)

A
  • Mast cells
  • Basophils
  • Enterochromaffin-like cells
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8
Q

Where are mast cells found in high concentrations?

A

Bronchial and intestinal mucosa

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9
Q

Histamine release causes the release of what cytokines?

A

Leukotrienes
Cytokines
Enzymes

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10
Q

What are the two MOAs of histamine release?

A

Cytolytic

Noncytolytic

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11
Q

What is the cytolytic histamine release pathway?

A

Membrane damage leads to high levels of histamine release

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12
Q

What cause cytolytic release of histamine?

A

High levels of drugs such as phenothiazine, H1 receptor antagonists, opioids

Mechanical damage

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13
Q

What is the noncytolytic mechanism of histamine release?

A

Immune response that requires prior sensitization, leading to displacement of histamine

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14
Q

What is the MOA of allergic reaction and histamine release?

A

Antigen binds in Ig ab (FC-epsilon-R1) receptor on plasma cells, that then produces IgE that integrate into mast cells.

The next time they stimulate mast cells directly throught IgE

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15
Q

What are the three major chemicals that are released during anaphylaxis, besides histamine?

A

Leukotrienes
Prostaglandins
Cytokines

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16
Q

What is anaphylactoid?

A

Clinical syndrome indistinguishable from anaphylaxis, but not caused by an immune response

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17
Q

Where is H1 receptor highly expressed (3)? What G protein?

A

Smooth muscle
Vascular endothelial cells
CNS neurons

Gq

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18
Q

Where is H2 receptor highly expressed (3)? What G protein?

A

Gastric parietal cells
Cardiac muscle
CNS neurons

Gs

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19
Q

Where is H3 receptor highly expressed (2)? What G protein?

A

CNS neurons
Peripheral sensory nerves

Gi/o

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20
Q

Where is H4 receptor highly expressed (3)? What G protein?

A

PMNs
Eosinophils
Monocytes

Gi/o

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21
Q

Where in the brain is there a large amount of histamine receptors?

A

Hypothalamus

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22
Q

What is the cyclical pattern of histamine levels? What is the function of this?

A

High in the day
Low at night

Functions in sleep and appetite

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23
Q

What is the transmitter that mediates itch? Where does this act?

A

H1 receptors in the periphery

Centrally and peripherally

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24
Q

What happens when H1 is activated in vessels?

A

NO released from PKC activation, causing vasodilation

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25
What happens when H2 is activated in vessels?
PKA causes vasodilation
26
What is the main receptor that mediates increased permeability of endothelial cells?
H1
27
H1 activation in the epidermis causes what? Dermis?
``` Epidermis = itch Dermis = pain ```
28
What histamine receptor increases airway fluid secretion?
H1
29
What type of histamine receptor is on the heart? Effect?
``` H2 Increased Ca (force and nodal speed) ```
30
Which response is greater: H1 vasodilation reflex tachycardia, or H2 receptor activation increase in HR?
H1
31
How does histamine help with immune system function?
Facilitate the accumulation of immune cells at the site of damage (p-selectins, integrins, and adhesions)
32
What WBC finding is found in CML? What is the significance of this?
Basophilia--can cause itching from histamine release
33
Gastric carcinoid tumors that secrete histamine cause what?
Episodes of vasodilation
34
What is mast cell leukemia? Ssx?
Mast cell proliferation causing Pruritus and flushing, diarrhea, and GERD
35
What is the drug that reverses the physiological effects of histamine?
Epinephrine
36
What are the three antihistamines that are release inhibitors of histamine?
Cromolyn Nedocromil Omalizumab
37
H1 receptor antagonism is used for what? H2?
H1 =Allergies | H2 = Gastric acid secretion
38
What are the H2 receptor antagonists?
Cimetidine and other-tidines
39
What are the side effects of the 1st generation of antihistamines?
Ach inhibition Alpha 1 inhibition 5HT Inhibition
40
What are the three major symptoms that are treated with 1st gen antihistamines?
Rhinitis Conjunctivitis Urticaria
41
What is the role of antihistamines in motion sickness?
Inhibit H1 receptors in the emetic center in the medulla
42
What are the receptors in the emetic enter of the medulla?
H1 M 5HT3
43
What does it mean when H1 antihistamines are inverse agonists?
bind and stabilize the inactive form of the histamine receptors
44
What are the adverse effects of H1 antihistamines on the CNS?
Decreased alertness/sedation
45
What are the adverse effects of H1 antihistamines in terms of the antimuscarinic effects?
Dry mouth Urinary retention Sinus tach
46
What are the adverse effects of H1 antihistamines in the terms of the serotonin receptor agonization?
Increased appetite and weight gain
47
What are the adverse effects of H1 antihistamines in terms of alpha adrenergic antagonism?
Dizziness | Postural hypotension
48
What is the MOA of Chlorpheniramine? What is this used to treat?
1st gen antihistamine Not an antiemetic, but allergies good
49
What is the major 1st generation ethanolamines? What is this used to treat? Side effects
Diphenhydramine (benadryl) Motion sickness and allergies, but causes sedation
50
How does diphenhydramine work as a local anesthetic?
Blocks Na channels in excitable membranes
51
What are the uses of Pyrilamine? MOA? Side effects?
Allergies 1st gen antihistamine Low sedation, no antimuscarinic or motion sickness
52
What is hydroxyzine used for? MOA? Side effects?
Antiemetic and anxiolytic 1st gen antihistamine has a lot of antimuscarinic effects
53
What is meclizine used for? MOA?
Motion sickness and vertigo 1st gen antihistamine
54
What is the use of promethazine? MOA? Side effects?
Antiemetic and local anesthetic 1st gen antihistamine Significant inhibition of alpha 1 adrenergic receptors and antimuscarinic effects
55
Promethazine is similar in structure to what drug? What does this mean?
Chlorpromazine Similar D2 antagonism, but lower potency
56
What is Cyproheptadine? MOA? What is it used for?
- Significant antiserotonin activity - 1st gen antihistamine -Anti-5HT to treat serotonin syndrome and causes weight gain
57
What are the four strongest antiemetic antihistamines?
Diphenhydramine Promethazine Hydroxyzine Meclizine
58
What are the three antihistamines that have the highest sedative effects?
Diphenhydramine Hydroxyzine Promethazine
59
What antihistamine has a very strong anti adrenergic action? What are the side effects of this?
Promethazine- Hypotension Dizziness
60
Which antihistamines have a strong anticholinergic effects? What are the side effects of this?
Diphenhydramine Promethazine Dry mouth Urinary retention Sinus tach
61
Which antihistamine has a strong anti serotonin effect?
Cyproheptadine
62
What class of drugs can intensify the anticholinergic effects of antihistamines?
MAOIs
63
What drugs have an additive effect on antihistamine sedative effect?
EtOH opioids Sedatives
64
True or false: most of the antihistamines are well absorbed in the GI tract
True
65
What are the enzymes that metabolize first gen antihistamines?
CYP2D6 and CYP3A4
66
What are the drugs that interact with p450s that antihistamines are metabolized by?
Imidazoles | Macrolides
67
What are the second generation of antihistamines (6)?
``` Azelastine Cetirizine Levocetirizine Desloratadine Loratadine Fexofenadine ```
68
What are the advantages of second generation antihistamines?
reduced lipophilicity | Higher selectivity
69
What is Azelastine? Use?
2nd gen antihistamine that also Inhibits histamine release from mast cells intranasal and ophthalmic
70
What are the two second generation antihistamines that have high sedative effects?
Cetirizine | Levocetirizine
71
Which 2nd gen antihistamine is minimally metabolized by the liver? Which is extensively metabolized by CYP3A4?
Fexofenadine | Loratadine
72
True or false: 2nd gen antihistamine are generally greatly affected by liver or renal dysfunction. Which one falls outside this commonality
False Fexofenadine metabolism is affected by renal dysfunction
73
Fexofenadine should be avoided while taking what drug? Why?
Antacids d/t reduced absorption
74
Grapefruit juice causes what interaction with 2nd gen antihistamines? How?
Reduce bioavailability d/t inhibiting p-glycoproteins
75
What is the MOA of Omalizumab? Use?
Recombinant humanized anti IgE Treats chronic urticaria and asthma
76
Which TCA inhibits H1 and H2 receptors? What is this used for?
Doxepin | Chronic urticaria
77
What is the MOA and use of ketotifen?
H1 antihistamine with additional mast cell and basophils stabilizing properties Allergic conjunctivitis
78
What is the MOA of Cromolyn?
Prevents the release of histamine from mast cells through inhibition of Cl channels
79
What is the MOA of nedocromil?
Prevents the release of histamine from mast cells through inhibition of Cl channels
80
What are the two major differences between the first generation H1 antagonists and second generation?
1st generation his a lot of other receptors, and does not cross the blood brain barrier

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