Antihistamines work by competing with histamine for histamine type 1 (H1) receptor sites in the blood vessels, GI tract, and respiratory tract. They block the physiologic effects of histamine.
The older, first-generation antihistamines cause more drowsiness, dry mouth, constipation, and other side effects than the second generation antihistamines. Antihistamines are taken daily. Administration at bedtime may help with drowsiness, but sedation and impairment may result in a “hang-over effect.” Second generation antihistamines are non-sedating antihistamines and they are preferred as first-line therapy.
Examples of first-generation antihistamines include:
The second-generation oral antihistamines are:
A limited number of studies comparing these agents suggest that there are no major differences in efficacy. Cetirizine causes drowsiness more frequently. Cetirizine (Zyrtec), fexofenadine (Allegra), and loratadine (Claritin) are available as antihistamine/decongestant combinations.
Intranasal antihistamines are an alternative to oral histamines. Here are examples of intranasal antihistamines:
Olopatadine intranasal (Patanase)
Next: Leukotiene Receptor Antagonists, Decongestants, Nasal Corticosteroids
Leukotriene Receptor Antagonists
Leukotriene receptor antagonists are non-steroidal medicines for preventing constriction of airway passages. These anti-inflammatory agents are alternatives to oral antihistamines. Montelukast (Singulair) is a leukotriene receptor approved for the treatment of seasonal and perennial allergic rhinitis. When used as a single agent, it is comparable to loratadine in reducing seasonal allergy symptoms.
Decongestants work by causing blood vessels in the nasal passage to constrict. Pseudoephedrine (Sudafed) produces weak bronchial relaxation and can increase heart rate and contractility. Decongestants are used in combination with antihistamines to treat nasal congestion.
Nasal steroid sprays are very effective fore treating allergic rhinitis. Nasal corticosteroids help control sneezing, itching, runny nose, and congestion. They are effective as monotherapy and studies have shown that nasal steroids are more effective than nasal cromolyn or antihistamines. Nasal steroids may be used as needed, but are maximally effective when used on a daily basis as maintenance therapy.
Available nasal corticosteroids include:
Next: Cromolyn, Ipratopium, Allergy Shots & Pills