Antihistamines for Treating Nasal Allergies

Histamine is a chemical released from allergic cells in the body (such as mast cells and basophils), usually in response to an allergen like cat dander or pollen.

When histamine is released by allergic cells in the nose and eyes, the result is sneezing, runny nose, itchy eyes/nose/throat, nasal congestion, and post-nasal drip. These are the symptoms of hay fever, also known as allergic rhinitis.

Antihistamines are medications that block the receptor for histamine, thereby stopping the symptoms that histamine causes. Antihistamines are the most commonly used medications to treat allergic rhinitis.

Older antihistamines, called first-generation antihistamines, include:

• Benadryl (diphenhydramine)
• Chlor-Trimeton (chlorpheniramine)
• Atarax/Vistaril (hydroxyzine)

These antihistamines have significant side effects termed “anticholinergic” side effects, which may include dry mouth, sleepiness, constipation, and urinary retention. Because of the side effects of these medications, they are generally considered to be too sedating for routine daytime use.

Therefore, this article will only discuss the newer antihistamines, as described below.

Newer antihistamines, called second-generation antihistamines include:

• Zyrtec (cetirizine)
• Allegra, generics (fexofenadine)
• Clarinex (desloratadine) 
• Claritin, Alavert, various generics (loratadine)
• Xyzal (levocetirizine) 

 These newer antihistamines tend to have fewer anticholinergic side effects and therefore are termed “low-sedating” or “non-sedating”.

It's important to note that montelukast (Singulair), is not an antihistamine, but rather an antileukotriene medication. Leukotrienes are chemicals released from a variety of allergic and immune cells and may cause allergy symptoms, primarily nasal congestion.

Antihistamines block the action of histamine, and histamine-related symptoms include:

• sneezing
• runny nose
• itchy eyes
• itchy nose
• itchy ears
• itchy throat

Other symptoms, including post-nasal drip, cough, and nasal congestion may also be caused by histamine, and therefore can be treated by antihistamines.

However, antihistamines are generally less effective at treating post-nasal drip and nasal congestion symptoms, since other chemicals other than histamine may be involved.

The answer to this question is completely based on my experiences and opinions as a board-certified allergist. Studies are very helpful in deciding which medication works best, but it also must be kept in mind which company is paying for the study.

It is my opinion that Zyrtec and Allegra are very closely matched, and very good antihistamines. I think these medications work much better than either Claritin or Clarinex. At the present time, I feel that Zyrtec is the best antihistamine available in the U.S. for the treatment of allergic rhinitis.

The topic of sedation is an important one. Sedation refers to the concept that someone feels tired. This is different than impairment, which refers to the concept that someone’s ability to perform various mental and physical tasks is affected.

The only truly non-sedating antihistamine currently available is Allegra. Zyrtec causes sedation five to ten percent more than placebo. Claritin and Clarinex cause minimal sedation. None of these second-generation antihistamines, when used in recommended doses for allergic rhinitis, have been shown to result in impairment. This is in comparison to the older antihistamines, such as Benadryl, which are well known to result in the impairment of mental and physical tasks.