I. Hydroxyzine Medication

Hydroxyzine Medication belongs to a group of medicines called sedating antihistamines.

Hydroxyzine medication's main use is to help in the treatment of anxiety. The way in which Hydroxyzine works in this condition is not fully known. It is thought to decrease the activity of certain areas in the brain and thereby relieve anxiety.

Hydroxyzine is also used to relieve symptoms of certain allergic reactions.

Histamine is a chemical produced by the body. It is stored in cells (mast cells) in almost all tissues of the body. When the body reacts to a foreign substance (an allergen e.g. flower pollen), the mast cells release their stores of histamine.

Histamine may then bind to receptors (H-1 receptors) in many areas of the body causing an increase in blood flow to the area of the allergy and the release of other chemicals that add to the allergic response. This stimulates the symptoms of an allergic reaction such as inflammation of the skin, airways or tissues, rashes, itching of the skin, eyes or nose, nasal congestion or narrowing of the airways.

Hydroxyzine acts by blocking the binding of histamine to receptors in the body and so preventing or relieving the typical symptoms of an allergic reaction.

Histamine may be released from and act in a small (localized) area of the body e.g. the nose. Alternatively, histamine can result in a serious or complete body reaction e.g. anaphylactic reaction. Hydroxyzine is only useful for the prevention or relief of localised or less serious allergies such as an itchy rash (rather than very serious allergic reactions).

Hydroxyzine is called a sedating anti-histamine as it enters the brain in significant quantities and is therefore more likely to cause drowsiness than the newer group of non-sedating anti-histamines.

Antihistamines: Information

Histamine is an important body chemical that is responsible for the congestion, sneezing, and runny nose that a patient suffers with an allergic attack or an infection.

Antihistamine drugs block the action of histamine, therefore reducing the allergy symptoms. For the best result, antihistamines should be taken before allergic symptoms get well established.

An allergy is a condition in which the body becomes unusually sensitive to some substance, such as pollen, mold spores, dust particles, certain foods, or medicines.

Common types of allergies

There are many kinds of allergies. Some of the most common types are:

• Indoor allergies – year-round, can be treated with medicine
• Outdoor allergies – seasonal, can be treated with medicine

These substances, known as allergens, cause no unusual reactions in most people. But in people who are sensitive to them, exposure to allergens causes the immune system to overreact. The main reaction is the release of a chemical called histamine from specialized cells in the body tissues. Histamine causes such familiar and annoying allergy symptoms as sneezing, itching, runny nose, and watery eyes.

As their name suggests, antihistamines block the effects of histamine, reducing allergy symptoms. When used for this purpose, they work best when taken before symptoms are too severe. Antihistamine creams and ointments may be used to temporarily relieve itching. Some antihistamines are also used to treat motion sickness, nausea, dizziness, and vomiting. And because some cause drowsiness, they may be used as sleep aids.

Histamines: Information

Histamine is an important protein involved in many allergic reactions. Allergies are caused by an immune response to a normally innocuous substance (i.e. pollen, dust) that comes in contact with lymphocytes specific for that substance, or antigen. In many cases, the lymphocyte triggered to respond is a mast cell. For this response to occur, a free-floating IgE (an immunoglobulin associated with allergic response) molecule specific to the antigen must first be attached to cell surface receptors on mast cells. Antigen binding to the mast cell-attached IgE then triggers the mast cell to respond. This response often includes the release of histamine.

The release of histamine (hist = because it's made up of histidine residues, amine = because it's a vasoactive amine) causes several allergic symptoms.
1) It contributes to an inflammatory response. 2) It causes constriction of smooth muscle.

Diagram 1: Histamine (Explanation for diagram: As more of the allergen enters your body, the antibodies "grab" the allergen. This triggers the basophils and mast cells to release powerful chemicals, including histamine.

Histamine can cause inflammation directly as well as indirectly. Upon release of histamine by an antigen-activated mast cell, permeability of vessels near the site is increased. Thus, blood fluids (including leukocytes, which participate in immune responses) enter the area causing swelling. This is accomplished due to histamine's ability to induce phosphorylation of an intercellular adhesion protein (called (VE)-cadherin) found on vascular endothelial cells. That is why histamine is known as being vasoactive. Gaps between the cells in vascular tissue are created by this phosphorylation, allowing blood fluids to seep out into extracellular space.

Indirectly, histamine contributes to inflammation by affecting the functions of other leukocytes in the area. It has been suggested by researchers that histamine release triggers the release of cytokines and inflammatory mediator by some neighboring leukocytes. These chemicals in turn increase the inflammatory response.

Histamine's second type of allergic response is one of the major causes for asthma. In response to an allergen (a substance that triggers an allergic reaction), histamine, along with other chemicals, causes the contraction of smooth muscle. Consequently, the muscles surrounding the airways constrict causing shortness of breath and possibly complete tracheal-closure, an obviously life-threatening condition. If the effects of histamine during an allergic reaction are inhibited, the life of an allergic person can be eased (in the case of inflammation) or even saved by preventing or shortening asthma attacks. Thankfully, many effective drugs have been developed to hinder histamine's allergic response activities.

Side effects of antihistamines

Common side effects of antihistamines include drowsiness, dizziness, poor coordination, restlessness, excitability, nervousness, and upset stomach. These problems usually go away as the body adjusts to the drug and do not require medical treatment. Less common side effects, such as dry mouth, nose, and eyes, irritability, difficulty urinating, and blurred vision, also may occur and do not need medical attention unless they do not go away or they interfere with normal activities.

If any of the following side effects occur, check with the physician who prescribed the medicine as soon as possible:

• Rapid, irregular, pounding, or fluttering heartbeat
• Convulsions
• Sweating
• Vomiting
• Fever
• Chills
• Fainting
• Breathing problems
• Hallucinations
• Unusual bleeding or bruising
• Low blood pressure
• Unusual sensitivity to light
• Uncontrolled movements.

Alternate Uses of Antihistamines

• Motion sickness
• Vertigo (severe dizziness)
• Nausea and vomiting
• Stiffness and tremors in patients with Parkinson's disease (diphenhydramine)
• Cough due to colds or hay fever (the syrup form of diphenhydramine)
• Insomnia
• Pre-operative sedation
• With narcotic analgesics for severe pain

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III. Useful links

http://www.cdc.gov/

http://www.fda.gov/

http://www.fda.gov/cder/ogd/

http://www.nih.gov/

http://www.ncbi.nlm.nih.gov/entrez/query.fcgi

http://www.health.gov.on.ca/

National Library of Medicine

World Health Organization

http://www.mayoclinic.com/index.cfm

MedicineNet.com

Drugdigest.org

Healthsquare.com

http://www.netdoctor.co.uk/medicines/100000192.html

http://www.entnet.org/healthinfo/allergies/antihistamines.cfm

http://www.zyrtec.com/index.asp?pid=3_0

http://www.bio.davidson.edu/courses/Immunology/Students/spring2000/lamar/mfirp.htm

http://www.swedish.org/16714.cfm

Pharmacy sites

http://www.roche.com/home/company/com_hist.htm

http://www.healthdigest.org/Bactrim-DS(Oral)_2006_PRO.php

http://www.hsforum.com/stories/storyReader$1509

http://www.hsforum.com/stories/storyReader$1516

http://www.hsforum.com/stories/storyReader$1504

http://www.people.vcu.edu/~urdesai/atc.htm#Process%20of%20clotting

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