Antihistamines are used to treat hay fever and other allergies. They work by preventing the effects of histamine, which is produced by the body. Histamine can cause itching, sneezing, runny nose, and watery eyes.
Allergic reaction occurs when our body’s immune system mistakes a harmless substance for a harmful one, and the body releases chemicals to fight it. This reaction is what causes the symptoms.
Hay fever is an allergic reaction to substances in the air like pollen. This can be indoors or outdoors. Besides pollen, one can have allergy to dust mites, or tiny flecks of skin and saliva shed by cats, dogs, and other animals with fur or feathers.
Allergic rhinitis refers to inflammation of the nasal passages due to the release of histamine and other mediators in the nose. Allergy testing helps with the diagnosis. Allergic rhinitis may be seasonal (usually due to grass, tree or weed pollens) or perennial (due to triggers such as pet hair, house dust mite or mould). Allergic rhinitis can lead to increased asthma symptoms.
Allergic conjunctivitis is another condition similar to allergic rhinitis. It can be seasonal due to pollens or perennial due to allergens present all year.
An article titled “How to use antihistamines,” was published in the Canadian Medical Association Journal (CMAJ April 6, 2021) which says, “Antihistamines are among the most commonly and incorrectly used medicines worldwide.”
The article says antihistamine use is most strongly supported for treating allergic rhino-conjunctivitis (hay fever) and urticaria (hives). It says we should not use antihistamines for conditions where antihistamines have questionable utility, such as in managing asthma, eczema, or cough.
Older (first generation) antihistamines are associated with substantial and sometimes fatal adverse effects. They cause sedation, injury and impairment in sleep. They interfere with mental and cognitive function, including impaired performance at school.
Older antihistamines should be avoided in the elderly. Overdose can result in death. Examples of older antihistamines are: Benadryl, Chlor-Tripolon, and Atarax.
The CMAJ article says, “Newer antihistamines are safer, as affordable and as efficacious as first-generation antihistamines.”
Compared with first-generation antihistamines, systematic reviews of randomized controlled trials have found newer antihistamines to be safer, longer lasting (12–24 hours) and faster acting. Their effect is felt in 50 minutes compared to 80 minutes for the first-generation antihistamines.
Warning – no antihistamine should be consumed with alcohol. And antihistamines should not be used for anaphylaxis. For this purpose, epinephrine is the drug of choice.
What you should know about second generation antihistamines.
Second generation antihistamines are newer medicines. Many treat allergy symptoms without causing sleepiness. The CMAJ article gives a summary of preferred antihistamines for allergy and urticaria: Bilastine, Cetirizine (Reactine), Desloratadine (Aerius), Fexofenadine (Allegra), Loratadine (Claritin), Rupatadine (Rupall).
It is important to remember some antihistamines are mixed with other medicines. These could include pain relievers or decongestants. These are meant to treat many symptoms at the same time. It is a good idea to treat just the symptoms that you have. If you have only a runny nose, don’t choose a medicine that also treats headache and fever.
There are other uses of antihistamines. For example: to prevent motion sickness, nausea, vomiting, and dizziness. In addition, since antihistamines may cause drowsiness as a side effect, some of them may be used to help people go to sleep, relieve anxiety, and produce sleep before surgery.
Start reading the preview of my book A Doctor's Journey for free on Amazon. Available on Kindle for $2.99!