Whatever are antihistamines?
Antihistamines, usually as tablets, are the basic
treatment of hayfever and some other allergic illnesses. They are also the main
treatment for a kind of skin rash called 'urticaria' or 'hives', also called 'nettlerash'.
In hayfever, the big advantage of antihistamines is that
they treat the nose, the eyes, and the terrible itching which some sufferers get
in the throat or ears. The only other treatments which help so many of the
symptoms are steroid tablets or injections, and desensitising injections. Both
of these other treatments have disadvantages not shared by antihistamines.
In hayfever the drawback of antihistamines is that they
are not so effective for the blockage in the nose which troubles some people.
Asthma is helped only slightly by
antihistamines; they are rarely used for asthma in Britain because there are so
many better medicines for that.
How do antihistamines work?
In allergic reactions special allergy cells in the
body release a chemical called histamine. Histamine causes rashes, sneezing,
itching and runniness of your nose, and the other features of allergic ailments.
It does this by causing blood vessels to widen and leak, nerves to itch,
secretions to pour from the lining of your nose or lungs, and in a variety of
other ways.So if we could just stop histamine from
working, we would help allergies.
Well, we can! Antihistamines do exactly this. They are chemicals
which look enough like histamine to fool the cells of the body, but not enough
like histamine to make the cells of the body do the nasty things which cause
allergy symptoms. (In technical jargon, they 'block histamine receptors').
In other words, antihistamines stop histamine from working
in the body.
But histamine is is not just involved in allergies. In fact
it plays a vital role in the brain. What it does in the brain is to keep us
attentive, alert, and awake.
So if we stopped all the histamine in the body from
working, we would get rid of allergy troubles, but fall asleep, or at least
become inattentive. This would make us dangerous drivers, bad students, and
generally bad at all the daily tasks which need alertness.
That is exactly what happens if you take old
antihistamines. They should not be used any more, except for special reasons,
such as when the doctor wants to make you sleepy.
Fortunately newer antihistamines help allergies with little
or no effect on your brain. How do they do this? It's very simple. Some
medicines hardly get into the brain from the blood. This is a disadvantage with
antibiotics for brain infections. But when research workers made antihistamines
which hardly got into the brain it solved the problem of sleepiness and
inattentiveness. So the new antihistamines are vastly better.
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