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Pharmacology Semester II > Exam III Antihistamines > Flashcards

Exam III Antihistamines Flashcards

1
Q

Antihistamines

A

Used for allergic rhinitis, eczema, uticaria

Insomnia

Motion sickness

GERD/PUD

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2
Q

Histamine

A

Vasoactive amine found in

Mast cells/Basophils -> defends against allergic reactions (immune) reactions

CNS -> Acts as Neurotransmitter

Gut -> regulates gastric acid production

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3
Q

Histamine release

A

Allergic / hypersensitivity reaction

Tissue injury

Direct mast cell destruction (drugs / chemicals)

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4
Q

Histamine receptors

A

**H1 – bronchial smooth muscle, CNS, Cardiac muscle – Sleep/Wake cycle, learning, memory, stimulate nerve endings, bronchoconstriction, vasodilation of blood vessels, contraction of smooth muscle.

**H2 – Parietal cells of stomach, cardiac muscle CNS – Gastric Acid production

H3 – CNS, peripheral tissue – Modulation of neurotransmitter release

H4 – Basophils, bone marrow, small intestine, colon, spleen, thymus – Facilitates mast cell chemotaxis

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5
Q

Cardiovascular effects of Histamine

A

More likely to be pronounced in preexisting cardiac disease

Inotropic effect

Hypotension secondary to vasodilation

Tachycardia

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6
Q

Histamine in immune modulation

A

Vasodilation -> capillaries permeable -> allows WBC to move in to site threat

  • Leads to Facial flushing and edema
  • Separation of endothelial cells -> urticaria
  • Induces fluid secretion – Gives rise to classic allergy symptoms —“Runny” nose, watery eyes etc
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7
Q

Histamine in parietal cells

A

Gastric acid secretion mediated by:

Histamine

Gastrin

AcH

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8
Q

Histamine in the CNS

A

Considered a Neurotransmitter

-H1,H3 receptors located in brain, some H2

Modulates:

  • ACH release -> learning & cognition
  • Alertness -> sleep wake cycle
  • Serotonin -> mood
  • Food intake -> suppression of appetite
  • Emesis center -> nausea / vomiting
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9
Q

H1 Effects of agonism

A

Bronchoconstriction

Diarrhea

Stimulation of peripheral nerves

Urticaria / edema

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10
Q

H1 Effects of antagonism

A

Bronchodilation

Constipation

Anti-itch, reduction of pain

Reduce inflammatory/allergic reaction

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11
Q

H2 Effects of agonism

A

Gastric Acid production

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12
Q

H2 effects of antagonism

A

Suppression of gastric acid

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13
Q

Histamine antagonists

A

Epinephrine -> works quickly/emergent

  • SM relaxation
  • A&B receptor stim

Cromolyn sodium -> works over weeks

-Stabilize mast cells, prevent degran

Antihistamines

  • H1 blockers-> txt allergies, insomnia, motion sickness
  • H2 blockers -> txt GERD/PUD
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14
Q

First gen H1 antihistamine Facts

A

Allergic symptoms / motion sickness / insomnia

-OTC & RX

Poor receptor selectivity

-Often interact with other receptors of other amines

–Anti-muscarinic, anti-alpha adrenergic, and anti-serotonin

Highly lipophilic!

-Crossees BBB to interfere with histaminergic transmission]

–Leads to many ADEs limiting use

Not preferred in elders

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15
Q

First Gen H1 Antihistamines

A

Doxylamine

Diphenhydramine

Cyclizine

Meclizine

Chlorpheniramine

Brompheniramine

Hydroxyzine

Promethazine

Cyproheptadine

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16
Q

Doxylamine & Diphenhydramine Clin Use

A

Insomnia, allergies

Highly sedating, large doses can cause arrythmias (QTc prolong)

Avoid in elders

+++ Anticholinergic effect - OTC

17
Q

Cyclizine & Meclizine Clin Use

A

Motion sickness

Vertigo

Mildly sedating

+ Anticholinergic effects – OTC/RX

18
Q

Chlorpheniramine & Brompheniramine Clin Use

A

Allergies

Moderately sedating possible paradoxical CNS stimulation

Often found in combo w/cold products

Avoid elder use

++ Anticholinergic effects - OTC

19
Q

Hydroxyzine Clin Use

A

HCL: allergies, urticaria

PAMoate: insomnia, anxiety

Mild-moderate insomnia, anxiety

+ And ++ Anticholinergic effects - RX

20
Q

Promethazine Clin Use

A

Anti-emetic

Highly sedating

a-blockade ->hypotension

D2-blockade -> dystonic reactions, akathisia

+++ Anticholinergic effect - RX

21
Q

Cyproheptadine Clin Use

A

Weight gain due to 5-HT2 blockade

+ Anticholinergic effect - OTC/RX

22
Q

ADE/DDI of 1st gen antihistamines

A
23
Q

ADE/DDI of 1st gen antihistamines DDIs

A

Metabolized via 2D6 and 3A4

Avoid:

  • Alcohol
  • Other Hypnotics and or Benzos
  • Tricyclic antidepressants (TCAs)
  • Acetylcholinesterase Inhibitors
24
Q

Second Gen H1 Antihistamines

A

Used to treat allergic symptoms only

Highly Selective for H1 receptor with no other receptor effects

Limited penetration of BBB

-Minimally or non-sedating

Preferred in elders

Rapid onset of action

Longer duration of action

25
Q

Second Gen H1 Antihistamines

A

Cetirizine

Azelastine

Levocetirizine

Fexofenadine

Desloratadine

Olopatadine

Loratadine

CALF LOD ine

26
Q

Azelastine and Olopatidine

A

Dual MOA: Mast Cell Stabilizer + H1 blocker

Local application -> less systemic effect

  • Local Irritation can occur (irritation, nosebleed, bitter taste/smell)
  • Avoid use in nasal passage damage

–RX – Nasal Spray—

27
Q

Fexofenadine

A

Highest safety profile

No CYP 450 metabolism

–Oral-OTC–

28
Q

Cetirizine

A

Most somnolence

Active metabolite of hydroxyzine

–Oral-OTC–

29
Q

Levocetirizine

A

Active metabolite of Cetirizine

–Oral-OTC—

30
Q

Loratadine

A

Metabolized via 3A4, 2D6 -> check for 3A4 inhibitors

–Oral-OTC—

31
Q

Desloratadine

A

Least likely to cause somnolence

Active metabolite of Loratadine

–Oral-RX—

32
Q

Potency of 2nd Gen H1 Antihistamines Most to Least

A

Desloratadine

Levocetirizine

Fexofenadine

33
Q

2nd Gen H1 Antihistamine ADEs

A

Somnolence

  • Usually at higher doses
  • Highest with cetirizine & levocetirizine

Constipation

HA

No sig Cardiac Effect

34
Q

2nd Gen H1 Antihistamine DDIs

A

Fexofenadine

  • NOT metabolized via CYP450 –> highest safety profile
  • Avoid grapefruit, orange, or apple juice

–Must separate by at least 4 hours

Loratadine, desloratadine

-Metabolized via 3A4 and 2D6 – Watch for DDIs Ketoconazole/grapefruit etc

Cetirizine, levocetirizine

  • Not metabolized via CYP450, but both are PgP substrates ->watch for DDI with Grapefruit juice
  • Avoid other sedative drugs -> additive effects
35
Q

H2 Receptor antagonist-Description

A

Reversibly decreases fasting and food stimulated acid secretion by inhibiting histamine at H2 receptor of parietal cell

Indicated for the treatment of mild-moderate, infrequent, episodic heartburn

-Good for on-demand, meal provoked symptoms

H2RA – onset:30-45 mins – Duration 4-10 Hrs.

36
Q

H2 Receptor antagonist-Misc

A

All H2Ras are equally efficacious – interchangeable

All are both OTC and RX

-OTCs about half strength

Well absorbed: absorption can be delayed by antacid but not food

-Bioavailability of cimetidine and ranitidine reduced with simultaneous high-dose antacid

37
Q

Available H2 receptor antagonists

A

Ranitidine

Nizatidine

Cimetidine

Famotidine

-Pepcid Complete Famotidine variant

R NiCe Fam tidine

38
Q

H2RA ADEs

A

Well tolerated

Most common are CNS related:

-HA, dizzy, fatigue, confusion

–Incident increased in elderly / renal impairment

Dose related gynecomastia occurs with cimetidine

Tolerance reported with prolonged use

-PRN

39
Q

H2RA DDIs

A

Drugs that depend on acid for proper absorption:

-Ketoconazole, itraconazole, protease inhibitors, calcium carbonate, iron salts

Cimetidine inhibits CYP450 (3A4, 2D6, 1A2, 2C9)

-Substrates: Cyclosporine, theophylline, warfarin, phenytoin. Amiodarone, antidepressants

Pharmacology Semester II (21 decks)

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