Antihistamines

Antihistamines

Histamine is one of the chemicals released when antibodies overreact to allergens. It is the cause of many symptoms of allergic rhinitis. Anti histamines can help relieve:

• Itching, sneezing, and nasal discharge
• Other allergy symptoms unrelated to rhinitis, including hives and some rashes
• Nasal congestion, for some of the newer antihistamines, such as cetirizine (Zyrtec) and desloratadine (Clarinex)

If possible, patients should take antihistamines before an anticipated allergy attack.

Many antihistamines are available. They include short-acting and long-acting forms and are available as tablets, nasal-inhalers, eye drops, and syrups. Antihistamines are generally categorized as first- and second-generation. First-generation antihistamines may cause more side effects than newer second-generation ones.

There are some notes of caution when taking any generation antihistamine:

• Antihistamines may thicken mucus secretions and can worsen bacterial rhinitis or sinusitis.
• Antihistamines can lose their effectiveness over time, and a different one may need to be tried.

First-Generation Antihistamines

First-Generation Antihistamines Ingredients and Brand Names. The older, so-called first generation antihistamines include:

• Diphenhydramine (Benadryl)
• Carbinoxamine (Clistin)
• Clemastine (Tavist)
• Chlorpheniramine (Chlor-Trimeton). Some health professionals recommend this drug if antihistamines are required during pregnancy. It may be as effective as the second generation antihistamines and much less expensive.
• Brompheniramine (Dimetane)

First-generation antihistamines contain compounds called anticholinergics, which tend to produce more side effects than second-generation antihistamines.

Side Effects

• Drowsiness and impaired thinking
• Dry mouth
• Dizziness
• Agitation
• Insomnia or nightmares
• Sore throat
• Rapid heart beat and chest tightness (uncommon and should be reported)
• Men with enlarged prostate glands may experience difficulty urinating

Drowsiness and First-Generation Antihistamines. Drowsiness is the most distressing side effect reported from first-generation antihistamines, and is potentially serious. It may pose a higher than average risk for work-related and automobile accidents than alcohol, narcotics, or prescription sedatives. However, some studies have not found any strong differences in sedation between the first- and second-generation antihistamines.Still, experts caution against the first-generation antihistamines for people most at risk from sedative effects, particularly elderly individuals. To reduce risks, take the antihistamine at home a few hours before bedtime, and do not combine it with alcohol or tranquilizers. Do not drive or operate heavy machinery.