Histamines and Anti-Histamines

Question 1

What agonists are antihistamines?

Answer 1

Inverse agonists

Question 2

Stimulation and functions of Histamines

Answer 2

IgE-bound to - Mast Cells, Granulocytes

• Bronchoconstriction
• Increase vascular permeability
• Vasodilation

Somatostain, Gastrin - ECL Cells, Stomach
- Gastric Acid

Sleep/Wake cycle; Itch/Pain

Question 3

Type of receptor for acute allergic rxn

Answer 3

H1, GPCR (all histamine receptors GPCR)

Question 4

M3 muscarinic function on eyes

Answer 4

Constrict Pupils by circular muscles, decrease light miosis
Contracts ciliary muscles, near vision, improves drainage

• Decreases IOP

Question 5

Old Generation vs New Generation Antihistamines properties and usage

Answer 5

Gen 1 for motion sickness, vertigo, N&V, Insomnia
Gen 2 for allergies
Anaphylaxis use adrenaline

Gen 1 sedating, with anti-adrenergic and anti-muscarinic side effects
Gen 2 non-sedating, poor CNS H1 specificity; Poor CNS due to less lipophilic, high affinity w efflux pumps, higher molecular weight

Question 6

Side effects of Old Gen

Answer 6

CNS: decreased alertness. psychomotor performance

Anti-muscarinic:

• bladder retention
• blurred vision
• dry mouth
• constipation
• sinus TC

Anti- alpha adrenergic (recall alpha function)
- limit vasoconstriction of visceral organs, blood vessels hence Postural Hypotension

Heart: V Arrhythmia, Prolonged QTc

Question 7

Contra I of Gen 1 antihistamines

Answer 7

BPH
Glaucoma (antagonize constriction of ciliary muscle, lens circular muscle, limit drainage and increases IOP)
Pilots

Question 8

DDI

Answer 8

Alcohol (liver problem and Sedative effects)
Opioid Analgesics (potentiating effects)

Question 9

Name Gen 2 antihistamines LCF

Answer 9

Cetirizine (Levocetirizine too)
Loratadine (Desloratidine too)
Fexofenadine