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Histamine is a substance produced by the body as part of its defence mechanisms. It is stored in cells called mast cells, in almost all tissues of the body. When the body reacts to a foreign substance (known as an allergen, eg flower pollen, pet fur, dust mites), the mast cells are stimulated by the allergen and release their stores of histamine.
The released histamine then binds to its receptors (H1 receptors), causing a chain reaction that results in allergic symptoms. It causes an increase in blood flow to the area of the allergy, and the release of other chemicals that add to the allergic response.
All this results in the symptoms of an allergic reaction. In hayfever, this causes inflammation of the nose, eyes, skin or airways and results in itchy watery eyes, a runny nose, sneezing and nasal congestion. Histamine is also responsible for the symptoms of allergic and itchy rashes, and allergic reactions to foods, medicines or insect bites. It can also cause more severe allergic reactions such as angioneurotic oedema, which involves severe swelling of the eyes, lips, tongue or throat.
Clemastine works by blocking histamine H1 receptors. It doesn't prevent the actual release of histamine from mast cells, but prevents it binding to its receptors. This in turn prevents the release of other allergy chemicals and increased blood supply to the area, and provides relief from the symptoms of allergies.
Clemastine is called a sedating antihistamine because it enters the brain in significant quantities and causes drowsiness.
What is it used for?
Warning!
Use with caution in
Not to be used in
This medicine should not be used if you are allergic to one or any of its ingredients. Please inform your doctor or pharmacist if you have previously experienced such an allergy.
Pregnancy and Breastfeeding
Certain medicines should not be used during pregnancy or breastfeeding. However, other medicines may be safely used in pregnancy or breastfeeding providing the benefits to the mother outweigh the risks to the unborn baby. Always inform your doctor if you are pregnant or planning a pregnancy, before using any medicine.
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