Many of the older antihistamines are now available OTC.
Many different preparations are available, and are derived from
six separate chemical classes. Although
these inexpensive OTC drugs are helpful in controlling
milder symptoms, they also cause various side effects.
Drowsiness and reduced mental alertness are particularly
common (seen in up to 50% of those taking the
medications). Cells that line the blood vessels in the
brain regulate which chemicals can enter the brain. These
cells are referred to as the blood brain barrier. The
reason these drugs induce sleepiness is that they are able to cross
the blood
brain barrier.
Table I: Common First Generation
Antihistamines
Generic Name
Brand Name
diphenhydramine
Benadryl
chlorpheniramine
Chlortimeton, Allerest
clemastine fumarate
Tavist
dexbrompheniramine
Drixoral
Allergy Alert
If you ask your pharmacist for the generic version of
your doctor's brand name suggestion, you may well get a
different preparation. Check that the generic name is the
same as the one your doctor recommended.
What are second generation antihistamines
(prescription)?
The newer antihistamines are available by prescription
only and are often referred to as "non-sedating." In
general, this group of antihistamines is more expensive,
has a slower onset of action, is longer acting, and induces
less sleepiness. Even some of these can be slightly
sedating (see Table II).
Allergy Alert
Two of the earlier second generation antihistamines,
Seldane (terfenadine) and Hismanal (astemizole), were
found to have unacceptable heart side effects and are no
longer available on the market.
Antihistamines perform best when taken regularly or
before an allergic reaction begins. The second generation
antihistamines may take up to an hour or more to become
effective. They should be taken well before an expected
allergic exposure, such as a visit to a friend who has a
cat.
Allergic rhinitis symptoms include an itchy, runny nose, sneezing, itchy ears, eyes, and throat. Seasonal allergic rhinitis (also called hay fever) is usually caused by pollen in the air. Perennial allergic rhinitis is a type of chronic rhinitis and is a year–round problem, often caused by indoor allergens, such as dust, animal dander, and pollens that may exist at the time. Treatment of chronic rhinitis and post nasal drip are dependant upon the type of rhinitis condition.
An allergy refers to a misguided reaction by our immune system in response to bodily contact with certain foreign substances. When these allergens come in contact with the body, it causes the immune system to develop an allergic reaction in people who are allergic to it. It is estimated that 50 million North Americans are affected by allergic conditions. The parts of the body that are prone to react to allergies include the eyes, nose, lungs, skin, and stomach. Common allergic disorders include hay fever, asthma, allergic eyes, allergic eczema, hives, and allergic shock.
Hay fever (allergic rhinitis) is an irritation of the nose caused by pollen and is associated with the following allergic symptoms: nasal congestion, runny nose, sneezing, eye and nose itching, and tearing eyes. Avoidance of known allergens is the recommended treatment, but if this is not possible, antihistamines, decongestants, and nasal sprays may help alleviate symptoms.
Common sources of indoor allergens include dust mites, cockroaches, molds, pets, and plants. Managing allergies caused by indoor allergens means reducing your exposure to them.
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