This study will evaluate a novel anti-Th2 therapy as a controller treatment of moderate-to-severe atopic dermatitis with the primary objective to prevent occurrence of disease flares, the major healthcare burden. OC000459 is an orally administered drug that inhibits the receptor CRTH2 expressed by Th2 lymphocytes, eosinophils and basophils. CRTH2 mediates recruitment of these leukocytes to inflamed skin and their activation to elaborate Th2 cytokines. CRTH2 is also implicated in the process of allergic sensitisation and its inhibition may therefore have long lasting disease modifying activity with the potential to halt the atopic march. OC000459 has proven efficacy in asthma and allergic rhinoconjunctivitis and therefore has the advantage of treating multiple co-morbid allergic diseases as a single systemic treatment.