Yes, you can feed your dog zyrtec in right dose. If you are not sure about the feeding amount, check with your vet first. Zyrtec (cetirizine) can be given once to twice daily. The adult tablets are both 10mg. Dogs under 10 pounds should get no more than 5mg, or 1/2 of a tablet. Those weighing 10-50 pounds should get 10mg, and heavy dogs (over 50 pounds) can take up to 20mg.