Allergy Treatment: Treatment: Antihistamines
A histamine antagonist, commonly called an antihistamine, is a pharmaceutical drug class which, as of 2015, includes two types of drugs: histamine H1-receptor antagonistsand histamine H2-receptor antagonists. Antagonists of the histamine H1-receptor are used to treat allergic reactions in the nose (e.g., itching, runny nose, and sneezing) and which are used off-label for insomnia. They are sometimes also used to treat motion sickness or vertigo caused by problems with the inner ear. Antagonists of the histamine H2-receptor are used to treat gastric acid conditions (e.g., peptic ulcers and acid reflux). They work by binding to histamine H1 receptors in mast cells, smooth muscle, andendothelium in the body and tuberomammillary nucleus the brain or histamine H2 receptors in the upper gastrointestinal tract, primarily in the stomach.
Histamine produces increased vascular permeability, causing fluid to escape from capillaries into tissues, which leads to the classic symptoms of an allergic reaction — a runny nose and watery eyes. Histamine also promotes angiogenesis.
Antihistamines suppress the histamine-induced wheal response (swelling) and flare response (vasodilation) by blocking the binding of histamine to its receptors on nerves,vascular smooth muscle, glandular cells, endothelium, and mast cells. They exert a competitive antagonism to histamines.
Itching and sneezing are suppressed by antihistamine blocking of H1-receptors on nasal sensory nerves.
Treating allergies can involve different medications, including steroids and allergy shots, but usually the first thing to try is an antihistamine.
How Antihistamines Treat Allergies
When your body comes into contact with whatever your allergic trigger is — pollen, ragweed, pet dander, dust mites, for example — it makes chemicals called histamines. They cause the tissue in your nose to swell (making it stuffy), your nose and eyes to run, and your eyes, nose and sometimes mouth to itch. Sometimes you may also get an itchy rash on your skin, called hives.
Antihistamines reduce or block histamines, so they stop allergy symptoms.
Antihistamines work well to relieve symptoms of different types of allergies, including seasonal (hay fever), indoor, and food allergies, but they can’t relieve every symptom. To treat nasal congestion, your doctor may recommend taking a decongestant. Some drugs combine an antihistamine and decongestant.
What Types of Antihistamines Are Available?
Antihistamines come in different forms, including tablets, capsules, liquids, nasal sprays, and eyedrops. Some are only available by prescription. Others you can buy over the counter (OTC) at your local pharmacy.
Examples of prescription antihistamines include:
- Astelin, Astepro (azelastine) nasal sprays
- Atarax, Vistaril (hydroxyzine)
- Clarinex (desloratadine)
- Cyproheptadine (generic only)
- Emadine (emadastine) eyedrops
- Livostin (levocabastine) eyedrops
- Optivar (azelastine) eyedrops
- Palgic (carbinoxamine)
- Xyzal (levocetirizine)
Examples of OTC antihistamines:
- Allegra (fexofenadine)
- Benadryl (diphenhydramine)
- Dimetane (brompheniramine)
- Claritin, Alavert (loratadine)
- Tavist (clemastine)
- Chlor-Trimeton (chlorpheniramine)
- Zyrtec (certirizine)
Eyedrops likes Emadine and Livostin treat symptoms of eye allergies, including itchy, watery eyes. Some medications, like Allegra-D, Claritin-D, and Zyrtec-D, combine an antihistamine and a decongestant to relieve congestion.
Side Effects of Antihistamines
Antihistamines can cause side effects, and some cause more side effects than others. Drugs such as Benadryl, Chlor-Trimeton, and Tavist and belong to an older group known as “first-generation” antihistamines. They tend to cause more side effects, particularly drowsiness.
Newer-generation antihistamines such as Allegra, Clarinex, and Zyrtec and have fewer side effects, so they may be a better choice for some people.
Some of the main side effects of antihistamines include:
- Dry mouth
- Nausea and vomiting
- Restlessness or moodiness (in some children)
- Trouble urinating or not being able to urinate
- Blurred vision
If you’re taking an antihistamine that causes drowsiness, try to take it before bedtime. Don’t take it during the day before driving or operating heavy machinery.
Read the label before you take an allergy drug. Antihistamines may interact with other medications you are taking.
Talk to your doctor first if you have an enlarged prostate, heart disease,high blood pressure, thyroid problems, kidney or liver disease, abladder obstruction, or glaucoma. Also check with your doctor if you are pregnant or nursing.
How antihistamines help
Antihistamines treat these allergy symptoms:
- Congestion, runny nose, sneezing, or itching
- Swelling of the nasal passages
- Hives and other skin rashes
- Itchy, runny eyes
Treating symptoms can help you or your child to feel better during the day and sleep better at night.
How to take antihistamines
Depending on your symptoms, you can take antihistamines:
- Every day, to help keep daily symptoms under control
- Only when you have symptoms
- Before being exposed to things that often cause your allergy symptoms, such as a pet or certain plants
For many people with allergies, symptoms are the worst around 4 a.m. to 6 a.m. Taking an antihistamine at bedtime may help you or your child feel better in the morning during allergy season.
What antihistamine is right for you?
You can buy many different brands and forms of antihistamines without a prescription.
- Some work for only 4 to 6 hours, while others last for 12 to 24 hours.
- Some are combined with a decongestant, a drug that dries up your nasal passages.
Ask your health care provider what type of antihistamine and what exact dosage is right for you or your child. Make sure you understand how much to use and how many times a day to use it. Be sure to read the label carefully. Or ask your pharmacist if you have questions.
- Some antihistamines cause less sleepiness than others. These include cetirizine (Zyrtec), desloratadine (Clarinex), fexofenadine (Allegra), and loratadine (Claritin).
- Do not drink alcohol when you are taking antihistamines.
- Store antihistamines at room temperature, away from heat, direct light, and moisture.
- Do not freeze antihistamines.
- Keep all medicines where children cannot reach them.