1. ANTIHISTAMINES
DR.FOUZIA

2. HISTAMINE
1-It is a chemical produced in mast cells.
Histidine  Histamine MAO
2-It mediates cellular responses like:
A- Allergic and inflammatory reactions
B- Gastric acid secretion
C- Neurotransmission in brain.
3-It has no clinical applications
4- Antihistamines have therapeutic applications.

3. HISTAMINE RECEPTORS
H1:
Pain and itching in the skin, bronchoconstriction, vasodilation
H2:
Gastric acid secretion by parietal cells in stomach, Cardio stimulant,
To ↓ histamine release from mast cells
H3:
Presynaptic modulation of histamine in CNS
H4:
Leukocytes (eosinophil), mast cells Chemotactic responses

4. CLASSIFICATION OF ANTI-HISTAMINES
H1-Antagonist:
First generation anti-histamines: (More sedation)
Chlorpheniramine
Cyclizine
Carbinoxamine
Dimenhydrinate
Diphenhydramine
Meclizine
Brompheniramine
Promethazine

5. CLASSIFICATION OF ANTI-HISTAMINES
H1-Antagonist:
Second generation anti-histamines:(Less sedation)
Fexofanadine
Loratidine
Desloratidine
Cetrizine

6. ANTIHISTAMINES
Mechanism of action:
1-H1 blockers are competitive antagonists of histamine at the H1-R
2-No effect on histamine release from storage sites
First generation
H1-R
Muscarinic-R
α1-R
Serotonin-R
Second generation
H1-R

8. CLINICAL USES OF ANTIHISTAMINES
1-Allergic and inflammatory conditions:
Allergic rhinitis
Hay fever
Allergic conjunctivitis
Urticaria
2-Anti-motion sickness:
Diphenhydramine, dimenhydrinate, cyclizine, meclizine, promethazine
3-Chemotherapy-induced vomiting
Diphenhydramine

9. CLINICAL USES OF ANTIHISTAMINES
4-Morning sickness in pregnancy:
Doxylamine (with pyridoxine)
5-Drug-induced parkinsonism:
Diphenhydramine( parentrally)
Acute suppression of extrapyramidal symptoms associated with
antipsychotics
6-As local anesthetics:
Diphenhydramine, Promethazine

10. ADVERSE EFFECTS OF ANTI-HISTAMINES
First generation
1-Sedation
2-Antimuscarinic effects
Dry mouth and blurred vision, urinary retention, tachycardia
3-Alpha-adrenoceptor blockade
Orthostatic hypotension (Promethazine)
4-Contact dermatitis
Diphenhydramine
5-Excitation and convulsions in children

11. ADVERSE EFFECTS OF ANTI-HISTAMINES
Second generation:
Headache
Arrhythmias (Terfenadine)

12. SEROTONIN
It is a local hormone, neurotransmitter
Receptors: 1-7
Clinical uses:
Serotonin agonist
1-BuspironeAnxiolytic
2-SumatriptanMigraine
3-Cisapride Gastro esophageal reflex and motility disorders
4-Tegaserod Irritable bowel syndrome

13. SEROTONIN
Clinical uses:
Serotonin antagonist
Cyproheptadine
1-Carcinoid tumor
2-Cold induced urticaria
Ondansetron
For nausea and vomiting associated with surgery and chemotherapy