The most appropriate treatment for this patient is an intranasal glucocorticoid. This patient has chronic cough (cough of more than 8 weeks' duration) due to upper airway cough syndrome (UACS) associated with allergic rhinitis. UACS is associated with conditions that cause excessive mucus production in the upper airways and postnasal drip, triggering cough. Allergic rhinitis is a frequent cause of UACS and is likely in this patient with evidence of seasonal allergies (clear nasal drainage, postnasal drip) and symptoms that are worse in high allergy seasons (fall and spring). Patients with UACS due to allergic rhinitis respond well to intranasal glucocorticoids, and these agents are considered first-line therapy.

Antibiotics are not indicated in this patient who has no clinical evidence of acute or chronic bacterial sinusitis.

First-generation antihistamine and decongestant therapy is recommended for patients with UACS due to nonallergic rhinitis. Since this patient's presentation is typical of seasonal allergies, intranasal glucocorticoids are a better option. Additionally, the systemic side effects associated with oral medications do not occur with intranasal administration.

Although cough can be a manifestation of asthma, this patient had no reports of wheezing, even with exercise, and physical examination did not reveal the presence of wheeze or airflow limitation. Therefore, inhaled bronchodilators are not indicated.