Antihistamines block the vascular effects of histamine to dry up a runny nose and watery eyes. Older agents like diphenhydramine (Benadryl) and chlorpheniramine (Chlor-Trimeton) work well, but side effects include drowsiness, dry eyes, constipation, and urinary retention. Second-generation antihistamines, classified as "nonsedating," include loratadine (Claritin) and cetirizine (Zyrtec).

Decongestants constrict the blood vessels of the nasal vasculature to reduce congestion. Products containing pseudoephedrine (Sudafed) are kept behind the pharmacy counter, while others containing phenylephrine (Neo-Synephrine) are on the shelves. Decongestants can increase blood pressure in susceptible individuals.

Other products: Cromolyn (NasalCrom) nasal spray is FDA approved for allergic rhinitis; it stabilizes the body's mast cells to reduce histamine release. Other products include eye drops that contain ocular antihistamines and decongestants to relieve itchy, red eyes.

JAMES M. WOOTEN, PharmD, a member of the RN editorial board, is an associate professor of medicine at the University of Missouri School of Medicine, in Kansas City, MO.

SOURCES: 1. Agency for Healthcare Research and Quality. Management of allergic and nonallergic rhinitis. 2002. www.ahrq.gov/clinic/epcsums/rhinsum.pdf (27 May 2008). 2. Prenner, B. M. (2006). Allergic rhinitis: Treatment based on patient profiles. Am J Med 119(3), 230. 3. Umland, E. M., and Thomas, E. A pharmacist’s guide to OTC therapy: Allergic rhinitis. 2005. http://www.pharmacytimes.com/issues/articles/2005-04_2158.asp (27 May 2008).