Can you give Claritin to a large dog?

NO. Please see your veterinarian if your dog seems to have symptoms of an upper respiratory problem or allergies, such as sneezing, coughing, difficulty breathing or harsh breath sounds, nasal discharge, or runny eyes. Dogs and cats should NEVER be given human medications, as their symptoms are often much different than ours, even in the same diseases, dosing for body weight is critically important, and even simple medicines like ibuprofen and acetaminophen can make animals critically ill to the point of death because their bodies metabolize these substances differently than we do. ALWAYS consult with your veterinarian if your animal seems to have a problem that you feel might improve with human medicines... you could be fatally mistaken.