Antihistamines and Allergic Rhinitis

Apr 15, 2014

By Trevor Shewfelt, Pharmacist at the Dauphin Clinic Pharmacy

3...2...1.. Blast Off!!! It actually worked! Erics rocket actually worked! I really had my doubts. Explosives, children, my complete lack of ability put things together properly. It shouldnt have gone that well. After a long, cold winter it was finally warm outside. It was the last weekend of Spring Break. It was about 1 C, no wind and lots of sunshine. Emily, Eric and I snowshoed to the middle of the field behind the house. We only needed to wear sweat shirts and sunglasses. Eric and I set up the rocket and got ready to launch. Emily was video taping us to put our potential diaster on YouTube if we injured ourselves in funny enough ways. But nothing bad happened. The rocket took off, well, like a rocket. It went straight up. The bright yellow chute openned against the blue sky. Eric didnt even have to run very far on his snowshoes to retrieve it.

Outdoor rocketry is a sign of spring. However with spring comes pollen. Spring pollens mean itchy watery eyes and stuffed up noses for many people. We call this condition allergic rhinitis. The usual quote is that about 10% of the population has hay fever or allergic rhinitis. However some estimates peg the number closer to 30-40%.

If we look inside the nose of someone with allergic rhinitis, there is a lot going on. Allergens, in this case pollens, are inhaled and bind to an antibody called IgE on the surface of special immune system cells called mast cells. These mast cells live in the lining of the nose called the nasal mucosa. After exposure to the allergens, mast cells quickly release a bunch of chemical signals. These signals include histamine, tryptase, vascular endothelial growth factor, and other inflammatory mediators. This leads to nasal itching and sneezing. Leukotrienes increase vascular permeability, causing runny nose and congestion. Then, 4 to 12 hours later, nasal congestion is increased due to the influx of different immune cells called T-cells, basophils, and eosinophils. These cells then release their own batch of chemical messengers.

Allergic rhinitis is when the immune system over reacts to pollens, which really arent a threat. The best way to avoid allergy symptoms would be to avoid the pollen. Some tips include using air conditioning instead of opening windows, showering and changing clothes after being outdoors and use a clothes dryer rather than hanging linens outside to dry. Frankly, though, if you go outside, you will probably be exposed. If you get allergic rhinitis, the most common over the counter medications we reach for are the antihistamines. Antihistamine medications block the histamine receptor which hopefully stops the allergic cascade and reduces the allergic rhinitis symptoms.

There is more than one type of histamine receptor that can be blocked. Some histamine receptors dont even affect allergies. For example, histamine blockers that block the H2 histamine receptor are used to reduce stomach acid. They have names like ranitidine and famotidine and we use them to treat heart burn and ulcers. To treat allergic rhinitis, we need to block the H1 histamine receptor.

There are two basic types of medications that block the H1 histamine receptor. We call these the first and second generation antihistamines. The first generation antihistamines are have names like chlortripolon (chlorpheniramine), and benadryl (diphenhydramine). They are inexpensive, work quite well, but they also often cause drowsiness, and some other side effects like urinary retention, and worsening glaucoma. They work fast, which is great if you have an itchy rash, but they dont last that long and you may have to take several pills a day. So they are cheap and fast, but have no staying power and might put you to sleep. So, they arent usually the first choice for allergic rhinitis.

Second generation antihistamines cause much less sedation, have far fewer side effects, but they are more expensive. These are agents like reactine (cetirizine), and claritin (loratadine). A nice benefit is one pill often lasts all day. Reactine is good for both runny noses and itchy rashes, but I have seen it make some people sleepy. Claritin only works well on runny noses, but it is much less likely to make someone sleepy. Between the two, I usually recommend the Claritin or loratidine for allergic rhinitis.

Spring is here. Im sure of it. We will have some warmer days and colder days, but the trend is to flowers, pollen, itchy watery eyes and runny noses. Ive seen an eight year old boy on snowshoes clad only in a sweat shirt and sunglasses chase a rocket. If that isnt a sure sign of spring, I dont know what is.

As always if you have any questions or concerns about these or other products, ask your pharmacist.

We now have this and most other articles published in the Parkland Shopper on our Website. Please visit us at www.dcp.ca

The information in this article is intended as a helpful guide only. It is not intended to be used as a substitute for professional advice. If you have any questions about your medications and what is right for you see your doctor, pharmacist or other health care professional.

 


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