Olopatadine hydrochloride (Patanol - Alcon), a propilidinedibenzoxypin derivative, has recently been marketed in a 0.1% ophthalmic solution for prevention of itching due to allergic conjunctivitis in adults and children more than three years old. It is the first drug for this indication that both inhibits mast cell degranulation and is a selective histamine H1 receptor antagonist (NA Sharif et al, J Pharmacol Exp Ther, 278:1252, 1996).

A 0.05% ophthalmic solution of levocabastine hydrochloride (Livostin - Iolab), a histamine H 1 -receptor antagonist, has been approved by the US Food and Drug Administration for treatment of seasonal allergic conjunctivitis. The new drug is a cyclohexylpiperidine derivative with no structural relationship to any other antihistamine.

Epinastine HCl, an H₁-receptor antagonist and mast cell stabilizer, has been approved by the FDA for use in a 0.05% ophthalmic solution (Elestat - Allergan/Inspire) for prevention of itching associated with allergic conjunctivitis. The drug is available orally in Europe and Asia.

Ophthalmic formulations of ketotifen fumarate (Zaditor), pemirolast potassium (Alamast) and nedocromil sodium (Alocril) have recently been approved by the FDA for use in adults and children with itching of the eyes due to allergic conjunctivitis.

Olopatadine 0.6% nasal spray (Patanase - Alcon) has been approved by the FDA for treatment of seasonal allergic rhinitis in patients ≥ 12 years old. An H1-antihistamine with mast-cell stabilizing activity, olopatadine is already marketed for treatment of allergic conjunctivitis in a 0.1% solution as Patanol and in a 0.2% solution as Pataday. Azelastine (Astelin), another H1-antihistamine with mast-cell stabilizing activity, has been available for intranasal treatment of allergic rhinitis since 1997.

The FDA has approved a nasal spray fixed-dose combination (Dymista – Meda) of the H₁-antihistamine azelastine (Astelin, Astepro, and generics) and the corticosteroid fluticasone propionate (Flonase, and generics) for treatment of seasonal allergic rhinitis (SAR) in patients ≥12 years old who need both medications for symptomatic relief. It is the first nasal spray to be approved in the US that contains both an H₁-antihistamine and a corticosteroid.