Antihistamines

Antihistamines are effective medications for reducing the symptoms of sneezing, itchiness, and runny nose, some of the most common symptoms associated with allergies. However, they are not very effective in treating nasal congestion. This is one reason why antihistamines are often combined with decongestants such as pseudoephedrine.

Histamine is a substance in the body that stimulates the production of mucus and the dilation (widening) of blood vessels. Allergy sufferers recognize histamine's effects as a runny nose and swollen nasal passages. Antihistamines prevent histamine from binding to histamine (H1) receptors, thereby blocking the histamine reaction. They are different from the medications called histamine (H2) blockers that are used to treat peptic ulcer disease and heartburn.

Drugs in this Class
Clemastine Tablets (Dailyhist-1, Tavist Allergy)
Azelastine Nasal Spray (Astelin)
Dexchlorpheniramine Solution (Dexchlorpheniramine Maleate Oral Solution, Dexchlorpheniramine Oral Solution)
Brompheniramine Tannate Oral Suspension (B-Vex Suspension, Brovex Suspension, J-Tan Suspension, TanaCof Suspension)
Dexchlorpheniramine Extended-Release Tablets  (Dexchlorpheniramine Maleate Extended-Release Tablets , Dexchlorpheniramine Tablets Extended-Release)
Cetirizine Tablets (Zyrtec)
Chlorpheniramine Maleate Tablets (Aller-Chlor Tablets, Allergy Tablets, Chlo-Amine Tablets, Chlor-Trimeton Allergy Tablets, Chlor-TrimetonTablets)
Carbinoxamine Tablets (Palgic)
Diphenhydramine Citrate Oral Disintegrating Tablets (Benadryl Children's Allergy Fastmelt Tablets)
Desloratadine Tablets (Clarinex Tablets, Desloratidine Tablets)
Loratadine Tablets (Claritin Tablets, Clear-Atadine Tablets, Tavist ND Tablets)
Cyproheptadine Tablets (Periactin)
Brompheniramine Maleate Oral Solution (J-Tan PD Drops, Vazol Solution)
Promethazine Tablets (Promethazine Hydrochloride Tablets)

Summarizing the Evidence

  • The older oral antihistamines, called first generation antihistamines, cause sedation in 20% to 35% of patients, but most patients build up tolerance to this side effect after a few days. First generation antihistamines include: brompheniramine, carbinoxamine, chlorpheniramine, clemastine, cyproheptadine, diphenhydramine, hydroxyzine, and promethazine.

  • The newer antihistamines, called second generation antihistamines, cause much less sedation and are longer acting than the earlier antihistamines. Second generation antihistamines include: cetirizine (Zyrtec), desloratadine (Clarinex), fexofenadine (Allegra) and loratadine (Claritin).

  • Allegra, Clarinex, Claritin, and Zyrtec are taken orally. Azelastine (Astelin), is another antihistamine that is available as nasal spray. Because Astelin is a nasal spray, individuals may not tolerate it as well as the antihistamine medications that can be taken orally.

  • Few scientific studies have been conducted comparing Allegra, Astelin, Clarinex, Claritin and Zyrtec; therefore it is difficult to determine if one is superior to the others in controlling allergy symptoms. The American Academy of Allergy, Asthma, and Immunology (AAAAI) clinical practice guidelines for allergic rhinitis notes that while comparisons in clinical effectiveness among the second generation antihistamines are limited, overall clinical effectiveness and patient acceptance for management of allergic rhinitis appear to be similar.

  • Generally, it is thought that all antihistamines are similarly effective in controlling allergy symptoms. It may take "trial and error" to see which drug is most effective for you.

  • Of the second generation antihistamines, Zyrtec has been shown to cause more drowsiness than Allegra, Clarinex, and Claritin. Drowsiness is one of the more important side effects that the second generation antihistamines claim to reduce compared to first generation antihistamines. Zyrtec may be less desirable than the other second generation antihistamines if drowsiness is a concern.

  • The American Academy of Allergy, Asthma and Immunology (AAAAI) recommends second generation antihistamines, nasal corticosteroids or intranasal antihistamines for the initial management of allergy symptoms.

Dosing and Administration

  • Clarinex, loratadine (Claritin), and Zyrtec can be dosed once daily, whereas Allegra is dosed once or twice daily. Astelin is used twice daily. The other antihistamines need to be taken more frequently unless they are extended-release forms of the medication.

Generic Availability

  • Astelin and Clarinex are not available generically. The other antihistamines are available as generics, and most are available as over-the-counter (OTC) products. The OTC antihistamines may be available under several different brand names. They are also marketed as combination products for the treatment of cold symptoms under different product names. All ingredients are listed on the package to allow patients to purchase only the ingredients they need.ul>

    Drug Interactions

    Some interactions between medications can be more severe than others. The best way for you to avoid harmful interactions is to tell your doctor and/or pharmacist what medications you are currently taking, including any over-the-counter products, vitamins, and herbals. For specific information on how the drugs interact and the severity of the interaction, please use our Drug Interactions Checker.

    Side Effects

    To view specific side effect information, please use our Side Effect Checker.

    Additional Information

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      Last Updated: March 2008

      Note: The above information is intended to supplement, not substitute for, the expertise and judgment of your physician, pharmacist, or other healthcare professional. It should not be construed to indicate that the use of the product is safe, appropriate, or effective for you. Consult your healthcare professional before taking any medication.

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