Antihistamines are a class of drugs used to block the production, effectiveness or release of histamine, which is a chemical that causes inflammation and other allergy symptoms. Histamine is the chief chemical that causes most of the symptoms of asthma and other allergic reactions. There are different types of antihistamine drugs that are used by physicians. Each type of drug can be used in patients requiring antihistamine relief.
Histamine H1-Receptor Blockers
H1-receptor blockers, or antagonists, were among the first marketed antihistamine drugs. These drugs do not prevent the release or production of histamine, but rather prevent histamine from binding to the H1-receptor, reports Oregon State University. By preventing this binding, the drugs prevent histamine from acting on the tissues of the body. Histamine is only able to function when it binds to the histamine receptors. H1-blockers are useful in treating allergic rhinitis, itching and sneezing. These drugs cause relaxation of the smooth muscles in the respiratory and digestive tracts. Examples of H1-receptor antagonists include azatadine, brompheniramine and clemastine.
Histamine H2-receptor Blockers
Histamine H2-receptor blockers, or antagonists, block histamine from binding to H2-receptors. These drugs are used to treat duodenal ulcers and gastric ulcers and prevent the recurrence of those ulcers, according to MayoClinic.com. Histamine can cause the release of acid in the stomach when it binds to H2 receptors. By blocking those receptors, H2-receptor antagonists drastically reduce stomach acid levels in the stomach and intestines. High levels of acid are associated with ulcers. H2 blockers are available as over-the-counter preparations or in forms that require a doctor's prescription. Famotidine, cimetidine and ranitidine are all examples are H2 receptor blockers.
Mast Cell Stabilizers
Mast cell stabilizers are a type of antihistamine used to control and prevent asthma attacks, according to the Palo Alto Medical Foundation. Mast cells are special cells in the blood and tissues that break open and release histamine and other chemicals when exposed to certain allergens. The released chemicals cause inflammation and other symptoms of asthma. Mast cell stabilizers prevent the mast cells from breaking down and significantly decrease the amount of histamine in the body. Examples of mast cell stabilizers include cromolyn sodium and Tilade. Side effects of mast cell stabilizers are cough, throat irritation, taste problems, headache and runny nose.
