Anti-histamin Drugs

Antihistamin Drugs
• Autacoids (local hormones): are substances have
differing structures
• It includes:
• histamine
• Serotonin
• prostaglandin
Histamine
Histamine mediates a wide range of cellular
response including:
– allergic and inflammatory
Release of histamine:
It is released as a primary response to some
stimuli such as destruction of cells as a result of
• cold,
• bacterial toxins,
• bee sting venom, or
• Trauma
• Drugs such as morphine
Mechanism of action
• Histamine acts on histamine receptors which
include :
• H1 receptor
• H2 receptor
• H3 receptor
• H4 receptor.
All types of histamine receptors have seven
transmembrane helical domines and
transduce extracellular signals by way of G
protein-mediated second-messenger system.
Actions of histamine
• H1 receptor produce:
• Exocrine secretion: increase nasal and bronchial
discharge.
• Bronchial smooth muscle: constriction of bronchial
smooth muscle causes symptoms of asthma.
• Intestinal smooth muscle: constriction cause
intestinal cramps and diarrhea.
• Sensory nerve ending: causes itching and pain.