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Clinical Pharmacology II > Antihistamines > Flashcards

Antihistamines Flashcards

1
Q

What medical conditions are antihistamines used for?

A 
Allergic Rhinitis
Eczema
Urticaria
Hives
GERD/PUD
Insomnia
Motion Sickness
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2
Q

What is histamine?

A

Vasoactive amine derived from the amino acid histadine

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3
Q

Where is histamine stored/found?

A

MAST Cells and BASOPHILS = allergic reactions
CNS = Neurotransmitter
Gut = regulates gastric acid production

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4
Q

Where are H1 receptors located?

A

Bronchial Smooth muscle
CNS
Endothelium
Cardiac muscle

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5
Q

What is the action of H1 receptors?

A 
Sleep wake Cycle
Learning 
Memory
Stimulates nerve endings
Bronchoconstriction
Vasodilation of blood vessels
Contraction of smooth muscle
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6
Q

Where are H2 receptors located?

A

Parietal cells of stomach
Cardiac muscle
CNS

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7
Q

What is the action of H2 receptors?

A

gastric acid production

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8
Q

Where are H3 receptors located?

A

CNS

Peripheral tissue

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9
Q

What is the action of H3 receptors?

A

Modulation of neurotransmitter release (ACh, DA, GABA, NE, 5-HT)

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10
Q

Where are H4 receptors located?

A 
Basophils
Bone marrow
Small intestine
Colon
Spleen
Thymus
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11
Q

What is the action of H4 receptors?

A

Facilitates mast cell chemotaxis

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12
Q

What two histamine receptors have drug therapy?

A

H1

H2

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13
Q

What are the cardiovascular effects of histamine?

A

Mast cells present in normal cardiac tissue and greatly present in diseased hearts

Enhances influx of Ca2+ into cardiac myocytes causing:
Increased contractility
Tachycardia
Hypotension secondary to vasodilation

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14
Q

What causes histamine to be released from mast cells on occasion?

A

mast cell injury like morphine use

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15
Q

What is the role of histamine in immune modulation?

A

Vasodilation causing capillaries to become permeable allowing for WBC to move into site of “threat”

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16
Q

What symptoms occur from histamine release in immune modulation?

A

Facial Flushing and Edema
Hives (urticaria) = separation of endothelial cells
Induces fluid secretion causing runny nose, water eyes

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17
Q

What is gastric acid secretion mediates by in parietal cells?

A

Binding of:

Histamine
Gastrin
Acetylcholine

This causes increase in cAMP and Ca2+ influx allowing HCl to be secreted

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18
Q

What does histamine do in the CNS?

A

It is considered a neurotransmitter

Modulates:
ACh release = learning and cognition
Emotional memory acquisition
Alertness = sleep-wake cycle
Serotonin = mood
Food intake = suppression of appetite
Emesis center = nausea/vomiting
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19
Q

What does an antihistamine do to H1 receptors?

A

Bronchodilation
Constipation
Anti-itch, reduce pain
Reduced inflammatory/allergic response

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20
Q

What does an antihistamine do to H2 receptors?

A

Suppression of gastric acid production

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21
Q

What are the histamine antagonists?

A

Epinephrine
Cromolyn sodium
Antihistamines = H1 and H2 blockers

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22
Q

What is epinephrine?

A

works quickly

smooth muscle relaxation

Stimulates alpha and beta receptors

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23
Q

What is Cromolyn Sodium?

A

works over several weeks

Stabilizes mast cells to prevent degranulation

24
Q

What do H1 blockers treat?

A

Allergies
Insomnia
Motion sickness

25
What do H2 blockers treat?
GERD/PUD
26
What are first generation H1 antihistamines?
Have poor receptor selectivity and often interact with other receptors of other amines having antimuscarinic, anti-alpha adrenergic, and antiserotonin effects Highly lipophillic and will cross the BBB with histaminergic transmission causing many ADRs
27
What first generation H1 antihistamines have severe anticholinergic effects?
Doxylamine Diphenhydramine Promethazine
28
Which first generation H1 antihistamines have mild anticholinergic effects?
Cyclizine Meclizine Hydroxyzine HCl Cyproheptadine
29
What is Doxylamine and Diphenhydramine?
Use: Insomnia, allergies ADRs: highly sedating, large doses can cause arrhythmias (QT prolongation) AVOID USE IN ELDERS OTC
30
What is Cyclizine?
OTC Use: motion sickness, vertigo Mildly sedating
31
What is Meclizine?
OTC, Rx Use: motion sickness, vertigo Mildly sedating
32
What is Chlorpheniramine and Brompheniramine?
OTC Use: allergies Moderately sedating, possible paradoxical CNS stimulation Often found in combo with "cold" products AVOID USE IN ELDERLY
33
What is Hydroxyzine HCl?
Use: allergies, urticaria | Mild-moderate sedation
34
What is Hydroxizine PAMoate?
Use: insomnia, anxiety | Mild-moderate sedation
35
What is Promethazine?
Use: anti-emetic | Highly sedating, alpha-blockade causing hypotension, dystonic reactions, akathisia
36
What is Cyproheptadine?
Use: weight gain | 5-HT blockade
37
What are the ADRs of first generation H1 antihistamines?
Cholinergic: dry mouth, urinary retention, sinus tachy Alpha-adrenergic: hypotension, dizziness, reflex tachy Serotonin: increased appetite Histamine 1: increased sedation, decreased cognitive and psychomotor performance, increased appetite
38
What are the DDIs of first generation H1 antihistamines?
Majority are metabolized via 2D6 and 3A4 Metoprolol TCAs Tramadol AADs Avoid with alcohol, other hypnotics and/or benzos, tricyclic antidepressants, acetylcholinterase inhibitors, and MAO inhibitors
39
What are second generation H1 antihistamines use to treat?
Allergic symptoms
40
What are second generation H1 antihistamines?
Highly selective for H1 receptors with NO anticholinergic effects Minimally or non-sedating due to limited penetration of BBB = preferred in elders Rapid onset of action Longer duration of action = once to twice daily dosing
41
What is Azelastine and Olopatidine?
Nasal Spray Rx only Local application to nose is associated with less sytemic side effects Local irritation can occur like nosebleeds and bitter taste or smell Avoid use if any preexisting damage to the nasal passage
42
What is Fexofenadine?
``` Oral, OTC Highest safety profile Not metabolized Excreted in feces DDIs: avoid grapefruit, orange, and apple juice = separate by 4 hours Not metabolized via CYP450 ```
43
What is Cetirizine?
Oral, OTC Most somnolence Active metabolite of hydroxyzine Not metabolized by CYP450 but is P glycoprotein substrate DDIs: grapefruit juice and sedative drugs
44
What is Levocetirizine?
Oral, OTC Active metabolite of cetirizine Not metabolized by CYP450 but is P glycoprotein substrate DDIs: grapefruit juice and sedative drugs
45
What is loratidine?
Oral, OTC Metabolized via 3A4, 2D6 Check for 3A4 inhibitors DDIs: Erythromycin, Ketoconazole, Clarithromycin, Cimetidine, and grapefruite juice
46
What is Desloratidine?
Oral, Rx Less likely to cause somnolence Active metabolite of loratidine DDIs: Erythromycin, Ketoconazole, Clarithromycin, Cimetidine, and grapefruite juice
47
What are the ADRs of second generation H1 antihistamines?
Somnolence at higher doses Constipation Headache No significant cardiac effects
48
Which two second generation H1 antihistamines have the highest risk of somnolence?
Cetirizine | Levocetirizine
49
What is the MOA of H2 receptor antagonists?
Reversibly decrease fasting and food stimulated acid secretion by inhibiting histamine on the histamine 2 receptor of the parietal cell
50
What is H2 receptor antagonists used to treat?
Mild-moderate, infrequent, episodic heartburn Good for on-demand, meal provoked symptoms
51
What are the characteristics of H2 receptor antagonists?
All available are equally efficacious All are available both OTC and prescription = OTC is usually 1/2 of the Rx Well absorbed; absorption may be delayed by administration of anatacid but not by food
52
What are the available H2 receptor antagonist?
Ranitidine Cimetidine Nizatidine Famotidine
53
What are the ADRs of H2 receptor antagonists?
Well tolerated CNS effects usually; often increased in the elderly Headache Dizziness Fatigue Confusion Dose related gynecomastia occurs with Cimetidine Tolerance has been reported with prolonged daily use
54
What is the limit for self-treatment with H2 receptor antagonists?
limit to no more than two times a day for no more than 2 weeks
55
What are the DDIs of H2 receptor antagonists?
``` Ketoconazole Itraconazole Protease Inhibitors (atazanavir) Calcium Carbonate Iron Salts ```
56
What is the ADRs and DDI's of Cimetidine?
ADR: Dose related gynecomastia DDI: Cyclosporine, theophylline, warfarin, phenytoin, amiodarone, antidepressants

Clinical Pharmacology II (25 decks)

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