Histamine

Question 1

What is it?

Answer 1

Neurotransmitter, neuromodulator, hormone
Stored in mast cell, basophils, enterochromafin cell,
Inflammation, gastric acid sceretion, allergy

Question 2

Receptor of histamine in smooth muscles, vascular endothelium and brain.?

Answer 2

H1
Bronchoconstriction
GI smooth muscle contraction
Pain
Increase heart rate
Vasodilation BP drop

Question 3

Receptor on mast cells, cardiac muscle, Gastric parietal cells, brain?

Answer 3

H2
BP drop due to vasodilation
Increase heart rate
Gastric acid secretion

Question 4

Receptor on CNS and gastric mucosa

Answer 4

H3
Increased satiety reduced appetite
Decreaes cAmp

H4:hematopoeitic tissue

H2 increas cAMP
h1 IP3 DAG Ca

Question 5

Triple response

Answer 5

H1 and H2
Small red spot at the centre of an intradermal injection of histamine
Edematous wheel around and red flare around the wheel

Question 6

Actions of H1receptor antagonists (inverse agonists)

Answer 6

❑ Sedation
❑ Anti nausea / Anti emetic (meclizine,diphenhydramine )
❑ Anti Parkinsons effect (diphenhydramine) cancer therapy induced vomit
❑ Anti muscarinic actions
❑ Alpha blocking effect (promethazine)
❑ Serotonin blocking effect (cyproheptadine)
Local anesthesia (promethazine, diphenhydramine)

Question 7

Toxicity of anitihistamines

Answer 7

Sedation
❑ Anti muscarinic effects
❑ Postural hypotension ❑ Convulsions in kids ❑ Rarely allergy

Question 8

Drug interactions of antihistamines

Answer 8

❑ Enzyme inhibitors like ketoconazole can potentiate toxicity ❑ Can have additive sedation with CNS depressants
❑ Additive effects with anti muscarinics

Question 9

Uses of antihistamines

Answer 9

H1:
Urticari
Angioedema
Seasonal rhinitis
Nausea in pregnancy
Motion sickness

H2
Acid production in PUD
Recurrent ulcers
Duodenal ulcers
Nocturnal acid secretion