Does a 24 hour antihistamine ( cetirizine hydrochloride 10mg) always last 24 hours? I took it at 7:30am. It's now 10:00pm and I'm having the same allergy symptoms for which I took it in the first place. Itchy eyes and nose, and feeling like I'm going to sneeze. Also some coughing. I'm asthmatic and also take symbicort. I used avamys nose spray earlier today. The allergies make my asthma worse. I have both indoor and outdoor allergies as well as food allergies.
Sometimes your allergies might overwhelm your meds. You can, however, take 2 zyrtec (cetririzine) a day - one AM and one 12 hours later - for 3-4 days until the allergies are under control...then go to one a day. I have had to do that a couple of times and was advised to do so by both my allergist and pharmacist.
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