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Timing is key
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Antihistamines are the mainstay of allergy treatment, but they must be used in a timely manner to prevent allergy symptoms
By Marie Berry Sniffles, sneezes, watery eyes — isn’t it time to reach for an antihistamine? But wait, it may be too late. Allergies affect from 10% to 20% of Canadians, but many more may have allergy symptoms they do not attribute to an allergy. Antihistamines are the mainstay of allergy treatment, but they must be used in a timely manner to prevent allergy symptoms.
Allergies are caused by allergens, such as pollen or poison ivy. When the allergen comes in contact with the body, perhaps by breathing in the pollen or by touching the poison ivy, an allergic reaction may result. The allergen fits together with an antibody — think of a jigsaw puzzle — and once together, they affect mast cells.
Mast cells are located throughout the body and contain vasoactive and inflammatory mediators like histamine. The allergen-antibody complex causes the mast cell to rupture and release its contents, like breaking open an egg. The mediators like histamine produce the itching, irritation and inflammation of allergies.
You must have antibodies that match the specific allergens in order to produce an allergic reaction, i.e. the jigsaw puzzle pieces have to fit together. There is a genetic tendency. If members of your family have allergies, you have a greater chance of having them. However, with repeated exposure, your body can develop its own antibodies. This explains why the first, second, or even the third time you were exposed to an allergen like poison ivy, you were not allergic. Your body needed these exposures to develop antibodies.
Antihistamines block histamine by competing at receptor sites with histamine. If more antihistamine molecules reach the receptor sites than histamine molecules, the allergy symptoms are avoided or reduced. That’s why you take antihistamines early, before histamine is released, to block as many receptor sites as possible, and prevent histamine from acting.
Two Groups
Antihistamines are classified in either of two groups based on their side effect profile as sedating or non sedating.
• Sedating antihistamines, first discovered in 1937, are referred to as classic antihistamines. Sedation occurs because this antihistamine group is readily able to cross into and affect the nervous system. Dizziness, lightheadedness, and drowsiness are the results. While sedation can be a bothersome side effect, precluding performing tasks that require mental alertness, it may mean a more restful night. Sedating antihistamines also have the ability to interact with other drugs that have sedation as a side effect.
Sedating antihistamines have other potential side effects, primarily anticholinergic:
• blurred vision,
• urinary retention,
• constipation,
• rapid heart beat
• dry mouth.
People with glaucoma, heart disease, chronic lung disease, or problems with prostate gland enlargement may not tolerate the above anticholinergic side effects.
Ironically, in some children and adults, sedating antihistamines can cause hyperactivity and insomnia. Nausea, especially for people with sensitive stomachs, and loss of appetite can also be problematic.
• Non sedating antihistamines, are the result of research begun in the 1970s. Astemizole (Hismanal) and terfenadine (Seldane) have recently changed status from non prescription to prescription because of their ability in combination with certain medications such as the antibiotic erythromycin to produce heart beat irregularities.
Alcohol should be avoided with all antihistamines. Pregnant women and nursing mothers should use them with care.
Antihistamines for allergies usually begin with the maximum recommended dose and are reduced for optimal maintenance. In overdose, antihistamines can produce sedation, disorientation, and even hallucinations.
How To Avoid Allergens
Pollens:
• stay indoors; hot, windy days spread more pollen while wet, rainy days “wash” pollen out of the air; higher pollen counts usually occur in the afternoon and late afternoon, but plants pollinate in the morning;
• avoid heavy pollinating trees like birch, ash, maple, poplar, oak and walnut; pollen from trees usually remains within several feet of the tree,
• dust and pollen masks can reduce exposure;
• air conditioning helps eliminate pollen in the house.
Animal Dander:
• avoid pets; washing a pet’s fur does not seem to reduce allergens.
House Dust and Mites:
• cover mattresses and pillows with dust-proof material or plastic;
• eliminate carpets, clean throw rugs, clean and dust thoroughly and regularly;
• clean furnace ducts and filters.
Mould and Spores:
• stay indoors, because moulds and spores are everywhere outdoors, and may be difficult to avoid; for example, snow mould is the crust left on the ground after snow has melted;
• inside the house, repair leaks, clean up mould on shower curtains, drains, etc.
Contact Allergens:
• for poison ivy, avoid contact and remember pets can transfer the allergen;
• for metal jewellery, a coat of clear nail polish will prevent contact;
• wear gloves and protective clothing.
Others Methods of Coping With Allergies
1. Saline nasal drops and sprays wash out accumulated mucous and allergens.
2. Cromoglycate stabilizes mast cells and prevents the release of histamine. Long used for asthma, this prescription product has recently become available as a non-prescription eye drop for the red, itchy, watery eyes associated with allergies. One draw back is that it has to be used frequently — four times daily.
3. Decongestants may be helpful if congestion is a problem and no counterindications are evident — for example with antihypertensives, antidepressants and thyroid medications. Decongestant sprays should be used for a maximum of 3-7 days, otherwise rebound congestion may occur. Those taken orally may produce a “wired feeling” or wakefulness.
4. Prescription steroid drugs like Prednisone tablets and beclomethasone nasal spray reduce inflammation. Steroid drugs are reserved for severe or chronic allergies.
5. Immunotherapy — allergy shots — is reserved for cases where all other avenues have been tried.
Common Questions About Allergies and Antihistamines
Q. Is there any way that I can determine what is causing my allergy symptoms?
A. A skin prick test may help your physician identify which allergens cause you most problems. A small amount of the allergen, e.g. ragweed pollen, is pricked into your skin and the reaction gives a good idea of whether you are allergic. Another, more straight forward method is to keep a diary of your activities and foods in relation to your allergy symptoms. You may be able to see a trend and identify the source of an offending allergen.
Q. I get hayfever in the spring, but isn’t hayfever supposed to occur more often in the fall?
A. Hayfever or allergic rhinitis is the group of symptoms experienced as a result of exposure to plants and plant pollen. Different plants produce pollen at different times of year — trees in the spring, grasses in the summer early fall, and ragweed in the fall.
Q. I’m allergic to cats, and I have to visit relatives who have cats. When should I take an antihistamine?
A. You should take an antihistamine at least half an hour to an hour before you go. The object is to make sure the antihistamine is in your body and blocking the histamine receptor sites before you encounter the offending allergens. Dosing is important Take the recommended dose for your age and size no more and no less. If your visit is prolonged, you may have to take more than one dose to be “protected” for the duration of your visit.
Q. Are antihistamines safe to give to children?
A. Antihistamines are safe for children, and many are formulated as liquids so they can be given to children. Make sure that the dose is correct for the age and size of the child, and remember that some children experience paradoxical stimulation with antihistamines.
Q. I have been using an antihistamine for over a year now. Is it safe?
A. Long-term antihistamine use is usually safe, as long as you do not have conditions that may preclude antihistamine use, e.g. thyroid problems, hypertension, glaucoma, prostate problems or liver disease. Make sure you are using the antihistamine for an allergy and not for something else that has similar symptoms, such as polyps. Chronic allergies should be evaluated because there may be a more appropriate therapy, e.g. steroid sprays.
Q. How do I tell the difference between an allergy and a cold?
A. Both allergies and colds are associated with a nasal discharge, congestion, sneezing and itching. With an allergy the nasal discharge is watery, copious and clear; with a cold, it is thicker, opaque and greener in colour. Sneezing and itching are more pronounced with an allergy. Watery, itchy eyes are seen with allergies. Colds are associated with coughs and sore throats, and last for about a week. Allergies last for weeks or months depending upon the duration of exposure to the allergen.
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