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Old 02-09-2019, 08:34 PM
asterion asterion is online now
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Does Xyzal have any advantage over Zyrtec?

Needing to get some new antihistamine, I found myself contemplating levocetirizine (Xyzal) vs cetirizine (Zyrtec). Is there any greater efficacy shown for the enatomerically pure version of the API over the racemic, or is it basically marketing and exploitation of available patent space? I did wind up with a generic levocetirizine, but the decision was purely based on cost.
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Old 02-09-2019, 08:54 PM
kayT kayT is offline
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My allergist told me Xyzal is not as strong as other OTC antihistamines. I don't know if it's true but in my experience almost all other antihistamines screw up my sleep patterns one way or another and Xyzal doesn't seem to do so. On the other hand my sleep patterns are pretty goofy all the time. On the other hand (3 hands!) I take antihistamines almost all the time since moving to Allergy Central (AKA Austin). So for what it's worth, I tend to take Xyzal most of the time (of course a generic).

And I don't have any idea what most of your second sentence means.
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Old 02-09-2019, 09:02 PM
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Yes, especially if you play it on a Triple Word Score.
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Old 02-09-2019, 09:41 PM
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Originally Posted by Thudlow Boink View Post
Yes, especially if you play it on a Triple Word Score.
Bravo!
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Old 02-09-2019, 10:05 PM
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Baron Greenback Baron Greenback is offline
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The US drug industry needs to invest in more vowels
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Old 02-09-2019, 11:12 PM
nearwildheaven nearwildheaven is offline
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Quote:
Originally Posted by kayT View Post
And I don't have any idea what most of your second sentence means.
The words "enantiomerically" and "racemic" are organic chemistry terms, and have to do with the molecule's 3-dimensional structure. In cetirizine's case, it has levo- and dextro-isomers (left- and right-handed structures of the same molecule) and they do have variable efficacy.

And yeah, it was a me-too drug to keep the patent active, but some people do find that one formulation or the other works better.
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Old 02-09-2019, 11:26 PM
kayT kayT is offline
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Thanks, nearwildheaven.
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Old 02-11-2019, 01:04 PM
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What I read is that levocetirizine is a particular isomer that has the same antihistamine effectiveness, but less drowsiness than regular cetirizine.

So for the same dosage, it should work the same but make you less sleepy. Or, I suppose you could take more without becoming sleepy (someone with some actual pharmacological knowledge can speak to that, not me!)
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Old 02-11-2019, 01:19 PM
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I'm on long term antihistamines for undetermined allergic response, and my doctor put me on Zyrtex because she said it had fewest side effects.
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Old 02-11-2019, 01:53 PM
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Usually in biochemistry, mirror isomers will end up having completely different effects. With a racemic mixture, you've got three possibilities: Either one isomer is active and the other is completely inert, in which case a doubled dosage of the mixture would be equivalent to a single dose of the pure active isomer. Or one is active in a way that we like, and the other is active in some completely unrelated way. Or both are active, and just happen to be complementary somehow such that the combination works better than either individually.

The third possibility is incredibly unlikely, and even if it were so, there would probably be some optimal ratio that wasn't 1 to 1, so you'd still probably want to isolate the two and dose them separately. In the second possibility, you'll get unwanted side effects from the other isomer, and so you'd be better off with the pure one. And the first possibility might happen, but unless the mixture is significantly cheaper than the pure form, you might as well go for the pure form anyway.
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Old 02-11-2019, 07:52 PM
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Qadgop the Mercotan Qadgop the Mercotan is offline
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Quote:
Originally Posted by Telemark View Post
I'm on long term antihistamines for undetermined allergic response, and my doctor put me on Zyrtex because she said it had fewest side effects.
I always found that zyrtec was the most sedating of the 'non-sedating' antihistamines, both personally and professionally.

Anyway, the most common side effects and their frequency for

zyrtec:
  • >10%:
    Central nervous system: Drowsiness (adults 14%; children 2% to 4%), headache (children 11% to 14%, placebo 12%)

    2% to 10%:

    Central nervous system: Insomnia (children 9%; adults <2%), fatigue (adults 6%), malaise (4%), dizziness (adults 2%)

    Gastrointestinal: Abdominal pain (children 4% to 6%), xerostomia (adults 5%), diarrhea (children 2% to 3%), nausea (children 2% to 3%; placebo 2%), vomiting (children 2% to 3%)

    Respiratory: Pharyngitis (children 3% to 6%; placebo 3%), epistaxis (children 2% to 4%; placebo 3%), bronchospasm (children 2% to 3%; placebo 2%)

vs Xyzal
  • >10%:
    Gastrointestinal: Diarrhea (infants: 13%; children: 4%)

    1% to 10%:

    Central nervous system: Drowsiness (3% to 6%), fatigue (adolescents and adults: 4%)

    Gastrointestinal: Constipation (infants: 7%), vomiting (4%), xerostomia (adolescents and adults: 2% to 3%)

    Otic: Otitis media (children: 3%)

    Respiratory: Nasopharyngitis (adolescents and adults: 4% to 6%), cough (children: 3%), epistaxis (children: 2%), pharyngitis (adolescents and adults: 2%)

    Miscellaneous: Fever (children: 4%)

So not a huge difference, but xyzal may be less sedating.
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