Nasal Allergy Medications (cont.)
What are first generation antihistamines (OTCs)?
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.
Table II: Second Generation Antihistamines
| Generic Name |
Brand Name |
Usual Dosage |
| loratadine (non-sedating)
| Claritin tablet/redi-tab 10mg, Claritin syrup 5mg/tsp
| 10mg once per day |
| fexofenadine (non-sedating)
| Allegra capsule 60mg
| 60mg twice per day |
| cetirizine (slightly sedating)
| Zyrtec tablet 5mg or 10mg, Zyrtec syrup 5mg/tsp
| 10mg once per day |
| azelastine (slightly sedating)
| Astelin Nasal Spray
| Two sprays in each nostril two times per day |
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.
Next: What are common side effects of antihistamines? »
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