ANTIHISTAMINES AND ALLERGIC RHINITIS

Apr 23, 2015

By Trevor Shewfelt, Pharmacist at the Dauphin Clinic Pharmacy

Albert Einstein was a pretty bright fellow. He said whether you are standing still, or speeding along in a rocket, light always moves at the same speed. That little statement has some big consequences. It means that if you travel in a rocket that approaches the speed of light, time moves slower for you than it does for me sitting on the ground. As you go faster and faster in your rocket, your mass will increase. And as your space ship flies by me, it will get shorter. All these strange predictions were just thought experiments to Einstein when he published Special Relativity in 1905. All of them have turned out to be true. These brilliant, strange predictions, among many others , revolutionized physics and how we think about the universe. Einstein was so brilliant at explaining the universe that people have always been interested in what he had to say about more mundane matters. One of my favorite Einstein quotes has always been The definition of insanity is doing the same thing over and over again and expecting different results

Spring can feel a little insane sometimes. We love to get outside. We love the longer hours of sunlight. We want to walk, ride our bikes and play in the garden. 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, which is 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. Thus, 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 occasionally 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.

I hope I explained antihistamines in a simple way that everyone could understand. Thats because Einstein had something to say about onerous explanations. If you can't explain it simply, you don't understand it well enough. I suppose that horrible explanation I gave off the top of Special Relativity belies my almost total lack of understanding about Relativity. We should leave that to the master as well. When you are courting a nice girl an hour seems like a second. When you sit on a red-hot cinder and a second seems like an hour. That's relativity.

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

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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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