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How does it work? of Antihistamine drugs
Antihistimines are drugs that block the action of histamine.
There are special histamine-receptor cells spread in tissues around your body. When the chemical histamine is released into the blood, it attaches to these receptor cells. This causes the blood vessels to widen, increasing blood flow to areas where there are receptors, such as the nose, which makes the area swell up and produce mucous, itching and other symptoms.
Antihistamines work by stopping histamine getting to the histamine receptor cells. This stops the blood vessels from widening, so prevents the allergy symptoms. The antihistamine drug also gets into your bloodstream and travels through the blood to your brain. Depending on the type of drug, it can act on the brain to produce other effects such as drowsiness, and to block the reflexes that make you vomit or cough.
There are two main types of histamine receptors. H1 receptors are mainly found in the small blood vessels in the skin, nose and eyes. Antihistamines that block H1 receptors are used to treat allergies, such as hay fever, that cause symptoms like itching, sneezing, and watering eyes.
H2 receptors are found mainly in the stomach lining. When histamine attaches to a H2 receptor, it releases acid into the stomach. Antihistamines that work on H2 receptors are therefore used to treat stomach ulcers. They stop acid being produced and give the stomach’s protective, mucous lining time to heal itself.
