ANTIHISTAMINES

Jun 24, 2013

By Trevor Shewfelt, Pharmacist at the Dauphin Clinic Pharmacy

 

Im failing as a parent, again. Do you itch to get out of bed in the morning? The early bird gets the worm, right? My son Eric cant wait to get out of bed. Eric has found that if he gets up earlier than anyone else, he doesnt have to share the iPad with his sister or mother. He can watch a movie or play a game without any interruptions. However, when Erics mean Dad catches him watching a movie at 5:45 am, Eric gets sent back to bed. I say Id like Eric to learn to rise early and get a head start on the day, but I punish him when I catch him performing the behavior. And all because Eric is itching to watch a movie without his sister.

 

If you get a sudden itch, or running nose or watery eyes, it could be an allergy. To treat allergic reactions, one of the types of medication we reach for are antihistamines. Oral antihistamines have been used for itchy watery eyes and runny noses since the 1940s. Antihistamines block the H1 histamine receptor inside the nose, lungs, eyes and skin.

 

Allergic reactions start more or less the same way. Your body comes in contact with what you are allergic to which is known as the allergen. Certain cells in your immune system release a chemical messenger called histamine in response to the allergen. The histamine fits into the H1 histamine receptor like a key into a lock which activates the H1 receptor. The activated H1 receptor tells your body to start having allergy symptoms like a runny nose, or an itchy rash. The easiest and best way to avoid an allergic reaction is to identify and avoid the allergen. For example, if you are allergic to the cat at your mother-in-laws house, avoid your mother-in-law. If that horrible cologne your wife bought gives you an itchy rash, dont use it. Simple, right? Well, even if we can identify the allergen, sometimes they are hard to avoid. If you are allergic to pollens that are common in Manitoba, you will probably get a stuffy nose in the spring no matter what you do. So if we cant identify and avoid the allergen, we may need to block the H1 histamine receptor with a medication.

 

We block the H1 histamine receptor with antihistamines. There are two basic types of antihistamines, first generation and second generation. They both work well, but their differences are speed, side effects and price. The first generation antihistamines are have names like chlortripolon (chlorpheniramine), and benadryl (diphenhydramine). First generation antihistamines block the H1 histamine receptor, but they also block other receptors. We call them poorly selective. That leads to some of their side effects like dry mouth, because they affect other receptors. First generation antihistamines are also lipophilic which means they can get through the blood brain barrier. The fact first generation antihistamines can get into the brain and effect histamine receptors there, leads to side effects like drowsiness. In summary, they are inexpensive, work quite well, but they also often cause drowsiness, and some other side effects like dry mouth, urinary retention, and worsening glaucoma. They work fast, which is great if you have a runny nose or an itchy rash, but they dont last that long and you may have to take several pills a day.

 

Second generation antihistamines cause much less sedation, last longer and have far fewer side effects, but they are more expensive. Second generation antihistamines are much more likely to only block the H1 receptor. We say this makes them much more selective. So we get fewer side effects like dry mouth. Second generation antihistamines are much less lipophilic. This means they are far less likely to get across the blood brain barrier and cause problems like sedation. These are agents like reactine (cetirizine), claritin (loratadine), aerius (desloratidine) and allegra (fexofenadine). 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. So they are more expensive, but have fewer side effects and more staying power.

 

Ive recommended antihistamines for itchy rashes for a long time. I even took them myself when I got swimmers itch at Clear Lake. I took fast acting diphenhydramine when I first got the itch. It helped the itch but made me sleepy. Over the next couple of days I took long acting cetirizine once a day. It didnt make me sleepy and also kept the itch away. However, my reading for this article says there is little proof that antihistamines work on all types of itches. In their 2005 paper in Dermatologic Therapy Michael ODonoghue and Michael Tharp looked at antihistamines as treatments for itch. They found antihistamines are very good at treating hives or uticaria, and the itch associated with hives. This is because there is a lot of histamine released when you get hives. However, there just hasnt been that much study about antihistamines and other types of skin itch. So, although we throw antihistamines at all sorts of itch as a first line treatment, we really dont have the science to back up that decision.

 

Itching to get out of bed early is a good trait for fishing, farming, being in the military, baking or being a morning radio host. Ive met many people over the years that say they get their best work done early in the day. I hope my kids grow up to seize the day and seize it early. Maybe Im a better parent than I think. Maybe when I punish Eric when he gets up early, I am making Eric want to get up ear ly even more because it is forbidden fruit. Maybe Im using reverse psychology. Or maybe, as usual, I just dont know what Im doing.

 

 

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.

 

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

 

 

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

 


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