Cetirizine, the active ingredient of Zyrtec ... Recommended dose for adults and children ages 6 to 64: One 10-mg tablet every 24 hours (maximum 10 mg per day) One to two 5-mg chewable tablets ...

or four tablets (10 mg) once a day, depending on symptom severity. Dosage guidance for Children's Zyrtec Allergy Relief syrup ...