(anti) Histamines Flashcards

1
Q

What is the chemical name of Histamine?

A

[2-(4-imidazole)-ethylamine]

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2
Q

What is the plasma half-life of Histamine?

A

5-10 min

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3
Q

What are the main enzymes involved in Histamine metabolism?

A
  • HNMT: histamine N-methyltransferase
  • DAO: diamine oxidase
  • MAO: monoamine oxidase
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4
Q

What are the cellular sources of Histamine?

A
  • ECL Cells (Enterochromaffin-Like Cells)
  • Mast Cells
  • Basophil
  • Histaminergic neurons
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5
Q

What are the biological actions of Histamine?

A
  • Smooth muscle contraction
  • Vasodilation
  • Increased vascular permeability
  • Immediate symptoms of wheal-and-flare reaction
  • Sensory neuron mediation of pain and itch
  • Stimulation of gastric acid secretion
  • Modulation of neurotransmissions
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6
Q

What are the main components released during Mast Cell degranulation?

A
  • Histamine
  • Serotonin
  • Leukotrienes
  • Prostaglandins
  • Tryptase
  • Chymase
  • Carboxypeptidase A3 (CPA3)
  • Heparin
  • Cytokines and chemokines
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7
Q

True or False: H1-antihistamines are considered competitive antagonists.

A

False

**Footnote
They are inverse agonists

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8
Q

What are the classifications of H1-antihistamines?

A
  • 1st Generation
  • 2nd Generation
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9
Q

Name two examples of 1st Generation Antihistamines.

A
  • Diphenhydramine
  • Chlorphenyramine
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10
Q

What are the preferred uses of 2nd Generation Antihistamines?

A
  • Allergic rhinitis
  • Allergic conjunctivitis
  • Allergic urticaria
  • Food allergy
  • Mastocytosis
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11
Q

Fill in the blank: 1st Generation Antihistamines are ________ antihistamines.

A

Sedating

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12
Q

What is a key difference between 1st and 2nd Generation Antihistamines regarding the blood-brain barrier (BBB)?

A

1st Generation can readily pass BBB, while 2nd Generation has lower lipophilicity and higher molecular weight.
Affinity to p-glycoprotein efflux pump

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13
Q

What is the duration for the onset of action for 1st Generation Antihistamines?

A

2-3 hours

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14
Q

What are common side effects of 1st Generation Antihistamines?

A
  • Drowsiness
  • Blurred vision
  • Dry eyes
  • Constipation
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15
Q

What is the duration of action for 2nd Generation Antihistamines?

A

24 hours (once daily)

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16
Q

What is the role of H1-Antihistamines in allergic disorders?

A
  • Relief of nasal itching
  • Relief of sneezing
  • Relief of rhinorrhea
17
Q

What type of allergic condition can be treated with Azelastine?

A

Allergic conjunctivitis

18
Q

What is the mechanism of action of H1-antihistamines?

A

They stabilize H1-receptors in the inactive form.

19
Q

What are the clinical uses of 1st Generation Antihistamines?

A
  • Motion sickness
  • Nausea and vomiting
  • Insomnia
20
Q

Fill in the blank: 2nd Generation Antihistamines have ________ H1-receptor specificity.

A

High

21
Q

Name one contraindication for the use of 1st Generation Antihistamines.

A

Patients with glaucoma

22
Q

What is a common side effect of 1st Generation Antihistamines related to psychomotor skills?

A

Drowsiness

23
Q

How is L-histidine converted to histamine?

A

Using histidine decarboxylase where CO2 is removed

24
Q

Give 2 examples of 2nd generation antihistamines.

A

Fexofenadine
Centrizine

25
Q

How does phosphatidylinositol pathway contribute to anti-inflammatory responses?

A

When GPCR is activated -> Gαq activated -> activates PLCβ -> PIP2 -> IP3 + DAG
1. Ca2+ regulation to increase gene expression of transcription factors like NF-κB and AP-1, which regulate cytokine production and promote expression of anti-inflammatory cytokines like IL-10
2. PLC activation eventually lead to promote transcription factors in lipid syntehsis -> AA is a precursor of lipoxins which reduce inflammation