- 10 Common Allergy Triggers Slideshow Pictures
- Take the Quiz on Allergies
- Nasal Allergy Relief Products Slideshow
- Nasal allergy medication facts
- Nasal allergy (allergic rhinitis) medication introduction
- Nasal allergy symptoms: an overview of treatments
- What's the difference between a controller and a reliever?
- What are antihistamines?
- How do antihistamines work?
- What are common side effects of antihistamines?
- What are decongestants?
- How do decongestants work?
- When should I use topical decongestants?
- What are side effects of decongestants?
- What about combination antihistamine/decongestant preparations?
- Nasal steroid sprays
- Other nasal sprays that might help
- Tips for proper use of nasal sprays
What are antihistamines?
The term "antihistamine" is a combination of two words; "anti-" means against, and "histamine" is a naturally occurring chemical that is released by the mast cells. Histamine is responsible for many of the signs and symptoms of allergic reactions, for example, swelling of the lining of the nose, sneezing, and itchy eyes. Histamine is released from histamine-storing cells (mast cells) and then attaches to other cells that have histamine receptors. The attachment of the histamine to the receptors causes these cell to be "activated," releasing other chemicals which produce the effects (symptoms, see previous sectiohn "Nasal allergy symptoms: an overview of treatments") that are associated with nasal allergies.
How do antihistamines work?
Human cells have three different types of histamine receptors (H1, H2, and H3). Histamine works by attaching itself to these receptors on the surface of cells and thereby causing its effects. It is mainly through the H1 receptors that histamine causes symptoms of nasal allergy. Antihistamines compete with histamine to attach to these same H1 receptor sites, thereby preventing histamine from binding to them. This action prevents histamine from causing allergic symptoms because the antihistamines that bind do not activate the cells.
Histamines can cause symptoms of swelling, sneezing, itching (nose, throat, roof of mouth), and a runny nose through the nostrils or down the back of the throat (post-nasal drip). Antihistamines are effective in treating the sneezing, post-nasal drip, and itching. They usually begin working between 30 to 60 minutes after being taken. However, histamine is only one of the many chemicals involved in the allergic reaction, which explains why relief from antihistamines is usually only partial.
Antihistamines have an interesting history. Bovet and Straub at the Pasteur Institute discovered the first antihistamine in 1937. It was too weak, however, and caused many side effects. In 1942, phenobenzamin (Antegan) was the first antihistamine used to treat allergies. Within a few years, diphenhydramine (Benadryl) and tripelennamine (PBZ) were formulated. These were the first and oldest generation of antihistamines
Many of the older antihistamines are now available OTC. Many different preparations are available, and are derived from six separate chemical classes. Although these inexpensive OTC drugs are helpful in controlling milder symptoms, they also cause various side effects. Drowsiness and reduced mental alertness are particularly common (seen in up to 50% of those taking the medications). Cells that line the blood vessels in the brain regulate which chemicals can enter the brain. These cells are referred to as the blood brain barrier. The reason these drugs induce sleepiness is that they are able to cross the blood brain barrier. The next table lists some common first generation antihistamines; these are widely available and may help people with nasal allergies sleep at night, but should not be used by people who need to be alert (driving vehicles or doing any action that involves high mental concentration) because they can be sedating.
|Generic Name||Brand Name|
Asking the pharmacist for generic version of the doctor's brand name suggestion or prescription requires caution. Check that the generic name and strength is the same as the medicine doctor recommended or prescribed.
The second generation antihistamines are often referred to as "non-sedating." In general, this group of antihistamines is more expensive, has a slower onset of action, is longer acting, and induces less sleepiness. However, even some of these can be slightly sedating, so the persons taking these medications should use them with caution (see table below). Two of the earlier second generation antihistamines, terfenadine (Seldane) and astemizole (Hismanal), were found to have unacceptable heart side effects and are no longer available on the market.
|Generic Name||Brand Name|
|certirizine (light sedation)||Zyrtec|
|azelastine (light sedation)||Astelin|
Antihistamines perform best when taken regularly or before an allergic reaction begins. The second generation antihistamines may take up to an hour or more to become effective. They should be taken well before an expected allergic exposure, such as a visit to a friend who has a cat, and that the person may be allergic to cat dander.
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