Welcome to the ultimate resource for mastering pharmacology! Our comprehensive pharmacology notes are specifically designed to help university students understand the main concepts of antihistamines as well as providing summaries of different types of antihistamines medication and their effects.
Antihistam
ines
Introduction
Hay fever and anaphylaxis
IgE antibody attaches to a mast cell
Re-exposure to an antigen (Ag) degranulation
Production and release of mediators
Mediator are localized-hay fever
Massive general release of histamine-
anaphylaxis (LIFE THREATNING)
Antigens-allergens
Mast Cells
Mast cells occur in almost all tissues
Contain Histamine
Release of Histamine involves the influx of
Ca2+ ions
↑Permeability of the cell membrane when
↑adenosine monosphosphate (cAMP)
Actions on the receptor
H1 receptor
- Pain and itching
- Bronchoconstriction
, - Vasodilation caused by release of nitric oxide
- Capillary endothelial cells-vasodilation-
↑permeability →local oedema
- Effects occur in allergic reactions
- Inhibit appetite and increases wakefulness
viaH1 receptors in the CNS
- H1 receptors-allergies, urticaria, anaphylactic
reactions
Histamine release by drugs, peptides,
venoms, and other agents
- Mechanical injury
- Many compounds stimulate histamine release
from mast cells directly, without prior
sensitization
- E.g. Tubocurine, succinylcholine, morphine,
some antibiotics, radiocontrast media, and
certain carbohydrate plasma expanders
- May account for unexpected anaphylactoid
reactions
- Some venoms e.g. wasp
Histamine H1 Antagonists
Oral, IV, topically
First generation agents
- E.g. Diphenhydramine, promethazine
- Highly sedating
- Significant automatic receptor-blocking
effects
- A newer subgroup of first-generation
agents
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