well i have given sarah zyrtec. my vet said one pill a day and sarah is 47 pounds. i would give 1/2 am and 1/2 pm but i know some who have given more. i have also used claritin. same thing 1/2 am and 1/2 pm if needed. i have also given chlorphenaramine. i think i used the 4 hour kind and 1 pill am and 1 pill pm but not sure didnt use that long. i think zyrtec works good for hives and runny nose. you can also give 1/2 zyrtec and then 1 benadryl later if that doesnt do it. my vet said it was safe and i have done this with sarah before. the claritin was ok but what works for one wont always work the same for another.