| An
antihistamine is a drug which serves to reduce or eliminate
effects mediated by histamine, an endogenous chemical mediator
released during allergic reactions, through action at the
histamine receptor.
Only agents where the main therapeutic
effect is mediated by negative modulation of histamine receptors
are termed antihistamines - other agents may have antihistaminergic
action but are not true antihistamines.
Antihistamine drugs are used to stop the
effects of a substance in the blood called histamine. Histamine
is a natural chemical produced by the immune (disease-fighting)
system of the body. When it is released, it increases blood
flow to the affected area. Liquid leaks out of the blood vessels,
making the mucous membranes lining the nose and throat to
swell, and stimulating nearby gland to produce mucus.
It causes symptoms such as itching, swelling,
or reddening. Histamine can also cause sneezing, running nose,
itchy or watery eyes, and in some people can cause breathing
difficulties.
The main action of histamine is related to
allergies. It is released when the body comes in contact with
an allergen. An allergen is a substance that isn’t normally
harmful, such as pollen, but which causes an over-reaction
by the immune system in some people. Histamine also has other
functions around the body, such as widening and tightening
blood vessels and squeezing muscles in your breathing and
digestive systems.
Antihistamine drugs are available as tablets
(oral), creams, and injections. The older antihistamines tend
to cause drowsiness (sedation is the medical term for drowsiness)
and rare dangerous heart arrhythmias (terfenadine and astemizole).
More recently developed, new antihistamines,
cause less drowsiness. The effects of ‘new’, non-sedating
antihistamines also tend to last longer, so you have to take
the medicine less frequently.
Antihistamine drugs prevent histamine carrying
out these actions. They are most often used to treat allergic
reactions, although certain types can be used in the treatment
of other conditions such as migraines, travel sickness, and
stomach ulcers.
Some antihistamines, such as creams for insect
bites, and some tablets for hay fever, can be bought over-the-counter
from your pharmacist. Others have to be prescribed by your
doctor.
What
are Antihistamine drugs? |
How
does it work? | What
is it used for? | Who
can use it?|
Side
effects|
Managing
Allergies During Pregnancy|
Asthma
in Pregnancy|
How
To Survive Spring Allergies|
Allegra
A Common Anti Allergy Drug|
Practical
Measures to Prevent and Treat Allergy|
Give
Your Allergies A Sniffle-Free Spring |
