Cetirizine dosage. Cetirizine is given as a single daily dose at a time during the day that works for you. It’s available as 5 milligrams (mg) and 10 mg tablets, 1 mg/mL syrup, and 5 mg and 10 mg chewable tablets, which can be taken with or without water and without regard to food consumption. Adults and children 12 years and older are recommended an initial dose of 5 mg or 10 mg per day, depending on how severe their symptoms are.