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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
Q

What do H2 blockers treat?

A

GERD/PUD

26
Q

What are first generation H1 antihistamines?

A

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
Q

What first generation H1 antihistamines have severe anticholinergic effects?

A

Doxylamine
Diphenhydramine
Promethazine

28
Q

Which first generation H1 antihistamines have mild anticholinergic effects?

A

Cyclizine
Meclizine
Hydroxyzine HCl
Cyproheptadine

29
Q

What is Doxylamine and Diphenhydramine?

A

Use: Insomnia, allergies
ADRs: highly sedating, large doses can cause arrhythmias (QT prolongation)
AVOID USE IN ELDERS

OTC

30
Q

What is Cyclizine?

A

OTC
Use: motion sickness, vertigo
Mildly sedating

31
Q

What is Meclizine?

A

OTC, Rx
Use: motion sickness, vertigo
Mildly sedating

32
Q

What is Chlorpheniramine and Brompheniramine?

A

OTC
Use: allergies
Moderately sedating, possible paradoxical CNS stimulation
Often found in combo with “cold” products
AVOID USE IN ELDERLY

33
Q

What is Hydroxyzine HCl?

A

Use: allergies, urticaria

Mild-moderate sedation

34
Q

What is Hydroxizine PAMoate?

A

Use: insomnia, anxiety

Mild-moderate sedation

35
Q

What is Promethazine?

A

Use: anti-emetic

Highly sedating, alpha-blockade causing hypotension, dystonic reactions, akathisia

36
Q

What is Cyproheptadine?

A

Use: weight gain

5-HT blockade

37
Q

What are the ADRs of first generation H1 antihistamines?

A

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
Q

What are the DDIs of first generation H1 antihistamines?

A

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
Q

What are second generation H1 antihistamines use to treat?

A

Allergic symptoms

40
Q

What are second generation H1 antihistamines?

A

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
Q

What is Azelastine and Olopatidine?

A

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
Q

What is Fexofenadine?

A 
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
Q

What is Cetirizine?

A

Oral, OTC
Most somnolence
Active metabolite of hydroxyzine
Not metabolized by CYP450 but is P glycoprotein substrate
DDIs: grapefruit juice and sedative drugs

44
Q

What is Levocetirizine?

A

Oral, OTC
Active metabolite of cetirizine
Not metabolized by CYP450 but is P glycoprotein substrate
DDIs: grapefruit juice and sedative drugs

45
Q

What is loratidine?

A

Oral, OTC
Metabolized via 3A4, 2D6
Check for 3A4 inhibitors
DDIs: Erythromycin, Ketoconazole, Clarithromycin, Cimetidine, and grapefruite juice

46
Q

What is Desloratidine?

A

Oral, Rx
Less likely to cause somnolence
Active metabolite of loratidine
DDIs: Erythromycin, Ketoconazole, Clarithromycin, Cimetidine, and grapefruite juice

47
Q

What are the ADRs of second generation H1 antihistamines?

A

Somnolence at higher doses
Constipation
Headache
No significant cardiac effects

48
Q

Which two second generation H1 antihistamines have the highest risk of somnolence?

A

Cetirizine

Levocetirizine

49
Q

What is the MOA of H2 receptor antagonists?

A

Reversibly decrease fasting and food stimulated acid secretion by inhibiting histamine on the histamine 2 receptor of the parietal cell

50
Q

What is H2 receptor antagonists used to treat?

A

Mild-moderate, infrequent, episodic heartburn

Good for on-demand, meal provoked symptoms

51
Q

What are the characteristics of H2 receptor antagonists?

A

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
Q

What are the available H2 receptor antagonist?

A

Ranitidine
Cimetidine
Nizatidine
Famotidine

53
Q

What are the ADRs of H2 receptor antagonists?

A

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
Q

What is the limit for self-treatment with H2 receptor antagonists?

A

limit to no more than two times a day for no more than 2 weeks

55
Q

What are the DDIs of H2 receptor antagonists?

A 
Ketoconazole
Itraconazole
Protease Inhibitors (atazanavir)
Calcium Carbonate
Iron Salts
56
Q

What is the ADRs and DDI’s of Cimetidine?

A

ADR: Dose related gynecomastia

DDI: Cyclosporine, theophylline, warfarin, phenytoin, amiodarone, antidepressants

Clinical Pharmacology II (25 decks)

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