Thursday, November 8, 2007

How Do Drugs Work - Antihistamines

Hello Everyone,

Tis the Season.

Well, Thanksgiving and Christmas are coming but that is not the season I am talking about.

I am referring to ALLERGY SEASON.

You go to bed one evening and you wake up in the morning with nose dripping, red eyes, scratchy throat, wheezing, sneezing, hives, and maybe throat tightness.

That is your body's immune response to a substance that is causing irritation in your nose and throat. The mast cells in your body are producing histamines. The histamines and the other chemicals that they stimulate are responsible for your runny nose and itchy eyes. Histamines can cause allergic reactions in other parts of your if you are allergic to peanuts or some prescription drugs.

To treat those symptoms, you need something to block the action of histamine. Something that works against the histamine, something that is "ANTI-histamine"

"Anti-Histamine" - Does that sound familiar?

Antihistamines are a class of medication that are used to counteract the action of histamines in the body. Specifically, they block histamine-1 receptors in the respiratory tract, GI tract and blood vessels. By blocking the receptors, the histamine is prevented from adhering or interacting with the receptors. The histamine can not then trigger the chemical cascade that then causes the symptoms that make you miserable.

Examples of antihistamines include chlorpheniramine (Chlor-Trimeton), diphenhydramine (Benadryl), clemastine (Tavist),fexofenadine (Allegra), loratadine (Claritin) and cetirizine (Zyrtec). The less-sedating antihistamines (Allegra, Claritin, Zyrtec) are available either by prescription or over the counter.

Side effects commonly include drowsiness and dry mouth. Because they can cause drowsiness, many people can not take antihistamines early in the day and you should not take them before driving or performing any other hazardous activities. I usually recommend to my patients to take antihistamines at night before going to sleep. In fact, many people take diphenhydramine so they can sleep! Antihistamines can cause difficulty urinating, confusion, and an increased risk for falls or injury especially in older adults.

Antihistamines are also useful for treating hives. There are antihistamine creams, lotions and gels that can be applied topically to treat itching on the skin.

There are other types of antihistamines. However, they are not usually known by that name. Remember, there are histamine receptors in the stomach. When those receptors are stimulated, it causes the acid producing cells in the stomach to produce acid. Histamine-2 blockers (H2 blockers) are used as an anti-acid treatment for treating heartburn. Examples of H2 blocker medication include ranitidine (Zantac) or cimetidine (Tagamet).

Please stay tuned to future posts concerning other medications to treat allergy symptoms such as decongestants. There are many patients that should not take decongestants because of their other medical conditions. Please be careful because there are many combination allergy treatments that contain both antihistamines and decongestants. Please read the label carefully or ask your pharmacist for advice. If the package says "Non-Drowsy Formula" - WATCH OUT. That usually means that it has a decongestant in it. We will go over that information soon.

Hope you stay healthy.

Dr. Paul

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