Allergic Rhinitis & Allergy: Understanding 1st & 2nd Generation Antihistamines
15
October

By Adem Lewis / in , , , , , /


Dr. David Fischer is the President of the
Canadian Society of Allergy and Clinical Immunology. He shares information regarding the over-reliance
on first generation antihistamines and related side effects by Canadians suffering from seasonal
allergies or allergic rhinitis, (an inflammation of the nose, who are seeking relief from
common aggravating symptoms such as a runny or stuffy nose, sneezing, or red, itchy, watery
eyes. At the Canadian Society of Allergy and Clinical
Immunology, we certainly have been frustrated over the years with the over-reliance of various
physicians prescribing first generation antihistamines, and technically pharmacists recommending them,
as well, as one of the first drugs of choice. We tend to view them as the last drug that
we would tend to recommend to our patients. In use for more than 75 years, first generation
antihistamines are widely available over the counter. They would include Benadryl, chlor-tripolon
and adderax which is available by prescription. These medications cause a significant amount
of drowsiness. Interestingly, from a drowsiness perspective,
Benadryl is sold as a sleep aid. So you can buy 50 milligrams of Benadryl as
a sleep aid or but you’re also taking it for your allergy symptoms during the daytime,
which is not making a lot of sense. While antihistamines may help you to fall
asleep, overall sleep quality is usually not very good. So, the sleep that you do well with, which
is called REM sleep, where you’re getting dreams, that sort of thing, that doesn’t
happen when you’re taking a first generation antihistamine. So, people think they’re doing a good thing,
because they’re taking the medication that will help them to fall asleep, but in fact,
they’re actually not getting good sleep. Benadryl should not be used when driving or
operating heavy machinery, but also when mental faculties are required to be optimal. There is a definite hangover effect in children. There are a few studies that were done that
looked at exam performance in children on first generation antihistamines. They did very poorly, actually. You also have something called anticholinergic
side effects. So, those are things where you get dry mouth,
dry eyes, dry nose…so you get a lot of significant dryness. And, you can actually have other side effects
which include dizziness, and so not just drowsiness, but dizziness during the day. Senior citizens taking these medications,
they’re at risk for falling, they are at risk for having a lot of urinary retention
issues and things that people aren’t always thinking about. There are options for allergy sufferers, which
provide effective symptom control but should not make you drowsy. These are second generation antihistamines,
commonly known as Allegra, Aerius, Claritin and Reactine, mostly available over the counter
at your pharmacy for some time in Canada. Additionally, Reactine is available by prescription
in higher dosage. The only drug that is different dose-wise
on prescription is Reactine. So Reactine, prescription-wise is 20 milligrams. Over the counter strength is 10. So, therefore, you are getting a slightly
higher dose of Reactine. The drawback of Reactine at 20 milligrams
is that it makes about 20% of people drowsy. So it’s not supposed to be undrowsy. It’s potentially drowsy. Prescription strength Reactine and Benadryl
are not prescribed for pilots. There is a study where they’re looking at
plane crashes, and they’re examining the blood of pilots. And 6% of them had Benadryl in their bloodstream. So, we know that certain drugs like Benadryl,
drowsy medications, are things that should be essentially forbidden for…pilots,
truck drivers, bus drivers, etc. For the first time in 20 years, there are
two new antihistamines available in Canada by prescription. So, after quite a number of years, 20 years,
we actually have 2 new antihistamines in Canada at pretty much, exactly the same time. So they’re both on prescription, and one
is Rupatadine, or Rupal. Rupal is the only new prescription indicated
for children ages 2 or older. And the other is Bilastine, or Blexten. Blexten is indicated for patients 12 years
and older. So they’re both on prescription, they’re
once daily and they’re quite non-drowsy. So those are all things to their benefit as
well. In clinical trials among 2nd generation prescription
antihistamines there are differences in the rates of sedation. As well, one should also consider whether
a product is processed in the liver, known as metabolism. Drugs that need to be processed by the liver
may lead to an increased likelihood of drug interactions. Dr. Fischer has one final message to share
regarding the use of antihistamines within allergies and allergic rhinitis. I want patients to know that I do have some
concerns if they’re taking a lot of Benadryl on multiple levels. I want them to be aware that these other medications
are available on prescription. You can seek them out, especially if you do
have drug plan coverage. And I want them to know that they are basically
safe, and a lot of people afraid of taking antihistamines on a regular basis, there’s
very little data to support that regular taking of them is a problem. A patient who is doing any of these new antihistamines,
you should speak to your pharmacist…there are some potentials for drug interactions
and that’s what your pharmacist is for. Please always speak with your pharmacist for
counsel regarding antihistamines and potential drug reactions or side effects.


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