According to Russell A. Settipane in an article in a 2003 issue of "Allergy and Asthma Proceedings," allergic rhinitis affects up to 30 percent of adults and 40 percent of children and is the sixth most common chronic disease in the United States. One of the first-line treatments for allergic rhinitis is antihistamine medications, including nasal sprays. Antihistamine nasal sprays—such as azelastine, sold as Astelin or Astepro, or olopatadine, brand name Patanase—have some side effects that are similar to other antihistamines, but some side effects are specific to the nasal route of administration as well.
When using an antihistamine nasal spray, the medication can drip down the back of the throat, which can cause a bitter taste in the mouth. One way to avoid this is to not tip the head back and to lean forward while taking the nasal spray, as noted on the University of Pittsburgh Medical Center website.
One of the side effects of antihistamine nasal sprays is epistaxis, or bleeding from the nose. According to the Mayo Clinic, the physician should be aware if the patient has any injuries to the nose or nosebleeds, because these medications can make these conditions worse. If a nosebleed occurs, the physician should be alerted.
Antihistamines can cause drowsiness, and antihistamine nasal sprays can cause this side effect in some patients as well. According to the Mayo Clinic, the combination of these nasal sprays with medications such as sedatives and sleeping medications could compound the symptoms of sleepiness. Before taking an antihistamine nasal spray, the patient should alert the doctor to other medications that might react with the nasal spray.
Another common side effect of antihistamine nasal sprays is headaches. This is typically related to constriction of blood vessels caused by the antihistamine activity, as noted in a 2009 presentation called "Respiratory Antihistamines" at Mercer County Community College. These headaches are typically temporary and generally resolve during treatment.
Dry mouth is another potential side effect of antihistamine nasal sprays. The antihistamine medication decreases the amount of saliva formed by the glands in the mouth, according to Mercer County Community College presentation. As with the side effect of headache, the dry mouth symptom is generally temporary and will go away with continued treatment.
The antihistamine nasal spray called olopatadine can cause urinary tract problems such as bladder pain, difficulty with urination or blood in the urine, as noted on the Mayo Clinic website. These problems could be very serious; if the patient notices these symptoms, the patient's physician should be contacted.