How much dosage of zyrtec can i have in a day? im 78 years old.. im having liquid food ensure, for over a month,, could this result in itching allergy

Possible: Ensure has ingredients (with dairy one of them) which can be allergenic. On the other hand, at your age, dry skin may be a more likely issue. Try unscented soap, apply moisturizer on your skin <3 mins after bathing and again in 12 hrs +/- bathing. Zyrtec would not help dry skin but you can take it up to 4 x daily if needed. For food allergy, avoidance is a must.