The incidence of respiratory allergy in the US has increased gradually over the past several years, and current estimates suggest that allergic rhinitis and bronchial asthma affect approximately 20% and 5% of the population, respectively. Rhinitis and asthma frequently coexist, and large-scale population surveys indicate that up to 38% of subjects with rhinitis have asthma, and up to 78% of subjects with asthma have chronic nasal symptoms. Safety concerns with the increased use of inhaled corticosteroids, the heterogeneity of the disease, and poor compliance with asthma medication regimens, point to the need for the development of safe and convenient oral therapies for asthma. Histamine is an important chemical mediator of inflammation in asthma. The benefits of antihistamine treatment in patients with mild to moderate asthma have been well documented, however their clinical use has been previously limited due to the high doses required for efficacy and their associated side effects including sedation and cognitive impairment.