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Xyzal: What Is IT and How Does IT Work? Dr.Peter Rice

Xyzal ™ – a right-handed nonprescription antihistamine

Last month I attended the annual meeting of the American Pharmacists Association in San Francisco. We had beautiful weather for the meeting, and I was able to visit with my cousin Terri who lives there. Terri is always happy to meet relatives visiting San Francisco as long as we don’t ask her to take us to Alcatraz – she has been there way too often to enjoy it.

Annual meetings of the profession are a good time to have some fun at the exhibits while catching up on the latest “big thing”. Xyzal is a newly marketed nonprescription second generation antihistamine, and I just happened to have had my picture taken with the product mascot, an owl wearing glasses and a bow tie. After I returned home I had several folks independently ask me about the drug, so it seems my blog friends might also be wondering about it.

Many patients are surprised to learn that drugs – much like people – can be right- or left-handed or ambidextrous. It’s a chemical thing. Most drugs contain the element carbon, and depending on the its chemical structure drug molecules can be left-handed, right-handed, or an equal mixture of each.

Xyxal ™ is levocetirizine, the right-handed molecule of the nonprescription antihistamine cetirizine, or Zyrtec™.

Both cetirizine and Xyzal ,levocetirizine act as second generation antagonists of histamine at the Histamine-1 receptor that mediates allergic responses. The drugs both have similar high affinity for the Histamine-1 receptor, but levocetirizine stays on the receptor better, so it is a better blocker as histamine concentrations change during an allergic response.

Xyzal, Levocetirizine, has some theoretical and practical advantages compared to cetirizine. In theory, levocetirizine is a cleaner medicine that should more specifically produce its effects. The presence of an other-handed molecule can sometimes interfere with metabolism or produce unwanted adverse effects. In the case of cetirizine, there does NOT appear to be any metabolic effects as both left- and right-handed forms are eliminated from the body through the kidneys rather than through metabolism.

Xyzal, levocetirizine, and cetirizine have similar pharmacokinetics; they are rapidly absorbed and can begin to act within an hour.

Interestingly, their half-life, a measure of their time in the body, is 6-9 hours depending on age. This suggests that even though they are marketed as once-daily drugs, some patients may find better results by taking half the daily dose twice daily.

With that said, the most reasonable question is whether you should take cetirizine or the newer Xyzal, levocetirizine.

It depends. If you’re doing well on cetirizine, you’ll likely do well on levocetirizine, but it will cost you. A comparison of the adverse effects suggests that Xyzal, levocetirizine, has many fewer adverse effects compared to cetirizine. No headache, much less gastrointestinal issues, bronchospasm. The major advantage of second generation antihistamines is that they do not cause drowsiness, but cetirizine and levocetirizine do not appear to differ in their drowsiness and fatigue.

If you are having issues with your antihistamine, it’s a good idea to try several and find which one suits you best.

  • These are drugs for symptomatic relief, so you will always be the one in the best position to tell which one helps you the most.
  • If you currently take cetirizine, Xyzal, levocetirizine is definitely worth a try.

There are always new drugs entering the market or being marketed in new ways. Your prescriber or pharmacist can answer your questions. Talk to your doctor who can help you make good choices with your medicines.

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Dr. Peter J. Rice

Dr. Peter J. Rice is a professor of Pharmacology emeritus at the East Tennessee State University Quillen College of Medicine and Professor of Clinical Pharmacy at the University of Colorado Skaggs School of Pharmacy and Pharmaceutical Sciences. He received his BS in pharmacy from Northeastern University, PhD in pharmacology from the Ohio State University and PharmD from the University of Kentucky. He is a Board Certified Pharmacotherapy Specialist and practices in the ambulatory care and community pharmacy settings. Professor Rice is the author of Understanding Drug Action: An introduction to pharmacology (APhA, 2014) and is a fellow of the American Pharmacists Association.




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