Antihistamines are medications that block the effects of histamine coming from the allergy cells in the body. There are currently three ways to get antihistamines; an oral pill, nasal spray and eye drops. The oral pills are things like diphenhydramine (Benadryl), cetirizine (Zyrtec), loratidine (Claritin), etc. Most of these are available over the counter and many times are mixed with decongestants.
The nasal spray forms are azelastine (Astelin/Astepro) or olopatadine (Patanase). These are most often used for allergic rhinitis, but can be useful in controlling some of the symptoms of AERD. There is one combination product that has both an intranasal steroid and an antihistamine. This is known as Dymista and can be a convenient way to get both medications in the nose.
Antihistamines in general may not be the most effective medications in AERD. They may not make a difference when taken on a daily basis, but certainly can be helpful add-on medications during a bad day. They are for the most part inexpensive and quite safe.