Nasal Allergy Medications (cont.)

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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.

Common First Generation Antihistamines
Generic Name Brand Name
diphenhydramine Benadryl
chlorpheniramine Chlortimeton, Allerest
clemastine fumarate Tavist-1
dexbrompheniramine Drixoral
hydroxyzine Atarax, Vistaril

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