Describe how antihistamines work.

Histamine is a Monoamine Neurotransmitter, which is formed via the decarboxylation of the amino acid Histidine. Histamine acts on H1-Histamine receptors which are dispersed throughout the body, most prominently on endothelial cells of capillaries and in mucous membranes such as those found in the Nasal, Oral and Pharyngeal cavities. Histamine is produced by granulocytes such as Basophills as well as Mast cells, these cells secrete Histamine in response to IgE activation upon the binding of foreign bodies such as pollen or dust. This results in the production of nitrous oxide by endothelial cells causing capillary lumen dilation and increased capillary permeability. This mechanism is responsible for symptoms such as a stuffy nose, increased mucous production and inflammation around the eyes. Antihistamines such as Cetrizine, Loratidine, Chloramphenicol, and Fexofenadine act as H1 receptor antagonists which prevent the binding of Histamine to its target receptor which inhibits the immune response which causes the symptoms of hayfever. Older antihistamines such as Diphenhydramine and Promethazine are no longer used due to their ability to cross the blood-brain barrier and antagonise H1 receptors of the Reticular Activation Centre which is responsible for alertness and stimulation of the frontal cortex of the forebrain. These older generation antihistamines are now re-branded as sleeping aids for insomnia.

Histamine is not only responsible for the modulation of allergic immune responses, it also plays a key role in the secretion of HCL by the Parietal cells of the Gastric glands of the stomach mucosa. However, Parietal cells do not express H1 histamine receptors but rather H2 histamine receptors. H2 antagonists such as Ranitidine were used in the management of acid reflux and gastritis since they reduced Gastric acid production. In modern medicine proton pump inhibitors such as Omeprazole and Lansoprazole are used more commonly.

When something foreign or abnormal is detected in the body, a protein called histamines are produced as a response. Histamines cause blood vessels to expand and the skin to swell - giving you the symptoms of an allergic response.

Anti-histamines work by blocking the action of histamines, either by attaching to the histamine protein and changing its shape or by attaching to the receptors that histamine attach to resulting in the histamine protein becoming ineffective.

Hi Saul

Allergies are exaggerated responses to certain antigens called allergens. Take hay fever as an example – when pollen grains enter the respiratory system, they may attach to the antigen binding sites of specific antibodies.

This induces cells to release histamine which brings about the typical symptoms related to allergies, including sneezing, teary eyes and muscle contractions which can inhibit effective breathing. Antihistamines block receptors for histamine diminishing the allergy symptoms.

Antihistamines work by blocking the effects of histamine, a chemical released during allergic reactions. This helps to alleviate symptoms like sneezing, itching, and runny nose, providing relief from allergies.

During the process of an allergic reaction, the body floods with histamine to try and combat against the irritant. However, the body often produces to much creating a cytokine storm. Anti-histamine combats against this issue.

Histamine is released in the body in response to harmful mediators, for example during an infection or an allergic response. It causes vasodilation and swelling. Antihistamines block histamine receptors and reduce swelling and are therefore taken to relieve symptoms of allergies, such as hay fever and reactions to bites or stings.

Anti-histamine work by inhibiting the effects of H1 receptors. They are a class of drugs commonly used to treat the symptoms of an allergic reaction such as swelling and itching etc.

When histamine is released by cells it travels around the blood stream and binds to histamine receptors on the surface of cells, this causes many of the symptoms associated with allergies. There are various types of histamine receptors : H1, H2, H3, H4, and H5. H1 is most commonly associated with allergies. Antihistamines have a similar chemical structure to histamine, this allows them to bind to the H1 receptors, however unlike histamine they don't illicit a response once they've bound. Once they've bound they block the receptor and prevent Histamine from binding and causing an allergic response.

Antihistamines work by blocking the effect of histamine. Histamines are released when the body detects something harmful in the body, antihistamines reduces the allergic reactions as well as symptoms.

Histamine is a chemical messenger involved in a number of complex biological actions. It occurs mainly in an inactive bound form in most body tissues. When released, it interacts with specific histamine receptors on the cell surface. There are four types of histamine receptors  H₁, H₂, H₃, and H_4.

Antihistamines are usually synthetically manufactured drugs that inhibit the effects of histamine by binding to the receptors.

H1 Antihistamines inhibit the action of histamine by competitively binding to the receptors and therefore blocking histamine from binding to H1 receptors. (these are usually used to relieve allergic reactions like hay fever)

Histamine also has a role in the regulation of the secretion of acid in the stomach. H2 antihistamines are very effective in the regulation of the secretion of acid and the hormone gastrin. They are therefore great for treatment of peptic ulcers (a condition caused by excessive secretion of gastric acid) .

Each antihistamines target the same receptor as the histamine thus inhibiting the effects of it e.g allergies or ulcers

Antihistamines are drugs used to stop the allergic effect of histamine , a substance produced in the body as a result of the body contact with allergic substances such as pollen, bee sting etc

Firstly, break down the process. Start with histamine. What is Histamine? It is a substance that your body produces when it detects something unusual/ harmful. So when this is released, the body reacts and produces an allergic reaction (Skin swelling, blood vessels expanding and all that). So then to counter that, us doctors prescribe a drug that contains antihistamines. These then go to the histamine "Channels" and block the effect of histamine so we do not have that "allergic reaction".

Antihistamines work by blocking the effects of histamine in the body. This substance is normally released when the body detects something that is potentially harmful such as an infection; histamine causes blood vessels to expand and swelling of the skin, which aids to protect the body.

Antihistamines are a drug class which work to treat a variety of medical issues. These include allergic rhinitis (runny nose), common cold, influenza and other allergens.

The mechanism of action for antihistamines is competitive receptor antagonism. Antihistamines prevent histamine from binding to H1 receptors and therefore preventing the outcome of the issues.

Antihistamines effectively block the effects of a chemical called histamine. These effects are often characterised by inflammatory responses, such as urticaria (hives) or blocked sinuses. Histamine is released when the immune system is exposed to an allergen or a xenobiotic. Antihistamines will block released histamine from binding to receptors, thus reducing symptoms.