For seasonal and perennial allergic rhinoconjunctivitis (runny/itching nose and red/itchy/watery eyes) and in chronic urticaria (itching), treatment is often with over the counter second generation H1 Antihistamines such as loratidine (Claritin). Studies have shown that these are most effective when taken on a regular basis than on an as needed basis to reduce allergic inflammation and prevent symptoms. Therefore your allergy drug would be most effective if it is taken on a regular basis during the duration of your symptoms.