How Long Does Zyrtec (Cetirizine) Last?

Answer

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Zyrtec (Cetirizine) is a second-generation antihistamine and lasts for about 24 hours per dose. It is most often dosed once daily although there are a few studies showing that 'double dosing' may be helpful for some individuals with severe allergies.

Additionally, there are few Zyrtec products on the market that last 12 hours instead of 24 and contain half the usual Zyrtec dose (e.g. Zyrtec-D 12-Hour).

There are a few other second-generation antihistamines that are also typically dosed once daily. These include:

• Allegra (Fexofenadine)
• Claritin (Loratadine).
• Xyzal (levocetirizine)

All of these antihistamines are available over-the-counter.

Second-Generaiton Antihistamine Info

As mentioned above, second-generation antihistamines are typically dosed once every 24 hours, but studies have shown that the effectiveness of these medications can wear off throughout the day. Allergy symptoms tend to worsen as it gets closer to the next dose, especially for those who suffer from seasonal allergies. This is where all antihistamines are NOT created equal.

There have been a few studies comparing the effectiveness of Zyrtec, Allegra, and Claritin over time. All medications typically work quickly, within 30 minutes to 1 hour but Zyrtec specifically seems to last the longest out of all 3.

The allergy symptoms experienced by subjects in the clinical studies were consistently less with Zyrtec over a longer period of time versus the other medications. So if you are looking for an antihistamine that lasts the longest, Zyrtec is probably your best bet. It should be noted however that Zyrtec does tend to cause drowsiness in some people.

Additional Zyrtec Info

​Duration Of Action: ~ 24 hours per dose

Half-Life: 6.5 to 10 hours

Children: Half-life reduced 33-60% when compared to adults

Elderly: Half-life prolonged 50% when compared to adults

Typical Dose: 10mg once daily

Final Words

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