Antihistamines are a group of medicines which act by blocking the action of the chemical called histamine in the body.Either H1 or H2 histamine receptors can be blocked by medicines, but the group commonly known as antihistamines blocks the H1 receptor.**Perennial allergic rhinitis**: This drug is indicated for the relief of symptoms associated with perennial allergic rhinitis due to allergens including dust mites, animal dander, and molds in adults and children 6 months of age and older.
For example, dry mouth, blurred vision and retention of urine.While this is a helpful response, it also causes redness, swelling and itching.Allergic reactions such as hay fever (seasonal allergic rhinitis) are caused by an oversensitivity or over-reaction of the immune system to a particular allergen.Desloratidine is also used for the sympomatic treatment of pruritus and urticaria (hives) associated with chronic idiopathic urticaria.Olopatadine is indicated for the symptomatic treatment of ocular itching associated with allergic conjunctivitis as ophthalmic solution.[L6781] In nasal spray, olopatadine is indicated for the symptomatic relief of seasonal allergic rhinitis in patients 12 years of age and older.[L6784]Intranasal azelastine is indicated for the symptomatic treatment of seasonal allergic rhinitis in patients 5 years and older and for the symptomatic treatment of vasomotor rhinitis in patients 12 years and older.[L8240] Ophthalmic azelastine solution is indicated for the treatment of itchy eyes associated with allergic conjunctivitis.[L8270]Levocetirizine is indicated to treat symptoms of perennial allergic rhinitis and uncomplicated skin manifestations of chronic idiopathic urticaria.[L7694] It is also used over the counter for a variety of mild allergy symptoms.[A181748]For symptomatic relief of nasal and non-nasal symptoms of seasonal rhinitis in patients 12 years of age and older and for symptomatic relief in chronic spontaneous urticaria in patients 18 years of age and older [FDA Label].