Antihistamines:

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

• Itching, sneezing, and nasal discharge
• Other allergy symptoms unrelated to rhinitis, including hives and some rashes
• Nasal congestion

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

Many antihistamines are available. They include short-acting and long-acting forms, and they come in form of 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 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 Antihistamine Ingredients and Brand Names. The older, so-called first generation antihistamines include:

• Diphenhydramine (Benadryl)
• Carbinoxamine (Clistin)
• Clemastine (Tavist)
• Chlorpheniramine (Chlor-Trimeton). Some health care providers 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. Although some studies have not found any strong differences in sedation between the first- and second-generation antihistamines, experts caution against first-generation antihistamines for people most at risk from sedative effects. 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. In general, second-generation antihistamines are now recommended as first-line therapy when antihistamines are used.

Second-Generation (Nonsedating) Antihistamines

The newer second-generation antihistamines do not usually cause drowsiness to the extent that the first generation antihistamines do. They are sometimes referred to collectively as nonsedating antihistamines. They are now generally recommended as first-line treatment when antihistamines are needed.

Brand Names. The second-generation drugs include:

• Loratadine (Claritin). Claritin is available over-the-counter and is approved for children ages 2 and older. Desloratadine (Clarinex) is similar to Claritin but stronger and longer-lasting. It is available only by prescription.
• Cetirizine (Zyrtec). Zyrtec is approved for both indoor and outdoor allergies. It is the only antihistamine to date approved for infants as young as 6 months. It is available over-the-counter.
• Fexofenadine (Allegra) is also available over-the-counter.
• Acrivastine (Semprex)
• Ebastine, norastemizole, levocetirizine, and mizolastine are other second-generation antihistamines under investigation in the U.S. and Europe. Some may prove to be useful for specific populations.

For nonprescription antihistamines, some studies suggest that cetirizine (Zyrtec) may be more effective than Allegra or Claritin in improving symptoms, including those in children. However, cetirizine can cause drowsiness when taken at high doses.

Side Effects and Precautions.

• Common side effects include headache, dry mouth, and dry nose. (These are often only temporary and go away during treatment.)
• Drowsiness occurs in about 10% of adults and in 2 - 4% of children.
• Uncommon side effects include rapid heart beat and chest tightness. Tell your doctor if these effects occur.
• Extended-release forms of Claritin and Zyrtec have other ingredients that can cause other symptoms, including nervousness, restlessness, and insomnia. Some patients taking Claritin-D 24 Hour Extended Release tablets have reported obstruction in the upper gastrointestinal tract, including difficulty swallowing.

Nasal-Spray Antihistamines

Azelastine (Astelin) and levocabastine (Livostin) are available in nasal spray form. They can reduce nasal congestion as well as allergy symptoms. Both reduce symptoms, although azelastine may be more effective in some patients. Their disadvantages are a bitter taste, drowsiness, and expense. They are not as effective as steroid nasal sprays.

Combination Antihistamines and Decongestants

Many prescription and non-prescription products that combine antihistamines and decongestants are available. Combinations sold over-the-counter include Allerest, Sudafed Severe Cold Formula, Vicks DayQuil, Benadryl Allergy/Sinus, Contac Day/Night Allergy & Sinus, and Zyrtec-D. Prescription combinations include Claritin-D and Allegra D. Symptoms may improve within 60 minutes, with congestion clearing up first.

Treating Itchy Eyes

Itching and redness in the eyes sometimes respond to oral antihistamines. Eye drops, however, provide faster relief, and a combination of the two may be best. The following are eye drops for itchy eyes. Others are also available. Individual responses vary, and patients need to find which specific treatment works best for them.

• Antihistamine eye drops: azelastine (Optivar), olopatadine (Patanol), ketotifen (Zaditor), levocabastine (Livostin) for relief of both nasal symptoms and itchy red eyes
• Decongestant eye drops: phenylephrine (Allergan Relief), naphazoline (Naphcon, Opcon-A, VasoClear), tetrahydrozoline (Murine Plus, Visine)
• Combination decongestant/antihistamine: Visine A
• Corticosteroids: loteprednol (Lotemax, Alrex), pemirolast (Alamast)
• Non-steroidal antiinflammatory eye drops: ketorolac (Acular)

General Side Effects and Warning.

• All eye drops can cause stinging, and some may result in headache and congestion.
• No one should continue taking eye drops if they experience pain, changes in vision, worsened redness, or irritation, or if the condition lasts more than 3 days.
• Do not touch the tip of the device to the eye or touch other surfaces with it. Replace the cap after using. Discard any solution that changes color or becomes cloudy.
• People who have heart disease, high blood pressure, an enlarged prostate gland, or glaucoma should talk to their doctor before taking these types of eye drops.