Scrabble?! ANTIHISTAMINICS

Definitions of ANTIHISTAMINICS in various dictionaries:

Antihistamines are drugs which treat allergic rhinitis and other allergies. Antihistamines can give relief when a person has nasal congestion, sneezing, or hives because of pollen, dust mites, or animal allergy. Typically people take antihistamines as an inexpensive, generic, over-the-counter drug with few side effects. As an alternative to taking an antihistamine, people who suffer from allergies can instead avoid the substance which irritates them. However, this is not always possible as some substances, such as pollen, are carried in the air, thus making allergic reactions caused by them generally unavoidable. Antihistamines are usually for short-term treatment. Chronic allergies increase the risk of health problems which antihistamines might not treat, including asthma, sinusitis, and lower respiratory tract infection. Doctors recommend that people talk to them before any longer term use of antihistamines.Although people typically use the word “antihistamine” to describe drugs for treating allergies, doctors and scientists use the term to describe a class of drug that opposes the activity of histamine receptors in the body. In this sense of the word, antihistamines are subclassified according to the histamine receptor that they act upon. The two largest classes of antihistamines are H1-antihistamines and H2-antihistamines. Antihistamines that target the histamine H1-receptor are used to treat allergic reactions in the nose (e.g., itching, runny nose, and sneezing) as well as for insomnia. They are sometimes also used to treat motion sickness or vertigo caused by problems with the inner ear. Antihistamines that target the histamine H2-receptor are used to treat gastric acid conditions (e.g., peptic ulcers and acid reflux). H1-antihistamines work by binding to histamine H1 receptors in mast cells, smooth muscle, and endothelium in the body as well as in the tuberomammillary nucleus in the brain; H2-antihistamines bind to histamine H2 receptors in the upper gastrointestinal tract, primarily in the stomach. Histamine receptors exhibit constitutive activity, so antihistamines can function as either a neutral receptor antagonist or an inverse agonist at histamine receptors. Only a few currently marketed H1-antihistamines are known to function as inverse agonists.