The Meda Pharmaceutical Inc, the US subsidiary of Sweden-based Meda AB, has filed a patent infringement suit against Mumbai-based Sun Pharmaceuticals Ltd in the United States District Court for the District of Delaware on the latter's Para IV filing to market the generic antihistamine nasal spray product in US.

The litigation is against Sun's Abbreviated New Drug Application (ANDA) 90-423 filed with the US Food and Drug Administration (FDA) to manufacture and sell generic spray product containing 0.1 per cent azelastine hydrochloride in aqueous solution for treating seasonal allergic rhinitis.

Meda Pharmaceuticals is currently holding the patent for the nasal spray product, marketed under the brand name Astelin. The product is patent-protected in the US until November 1, 2010 and thereafter with paediatric exclusivity until 1 May 2011, claims Meda Pharma.

In the petition to the District Court of Delaware, Meda Pharma alleged that Sun Pharma has infringed `194 patent in US and prayed not to approve the marketing rights to the latter till the expiration of the patent, including any extensions. The US patent `194 for azelastine containing medicaments has been valid since 1992. Meda Pharma is currently engaged in similar litigation with the Canada-based Cobalt Laboratories for the same brand.

According to the interim report of Meda AB announced in March 2008, Astelin for allergic and non-allergic rhinitis treatment, recorded sales worth Swedish Korona (SEK) 405 million at the time and US sales was of USD 57 million.

The company, in April 2008, has also settled a patent infringement issue with the Canada-based generic company, Apotex Corporation and its US subsidiary, for exclusive rights of Astelin and Optivar, the azelastine hydrochloride ophthalmic solution of Meda Pharma. As per the information available, the settlement agreement allows Apotex, alongside Meda's own sales, to launch a generic version of Astelin, licensed from Meda Pharma, on March 2010. Apotex may also launch a generic version of Optivar in December 2009 without further payment obligation to Meda Pharma.

Meda Pharma has already filed a complaint against Sun Pharma regarding a proposed generic version of Optivar in the end of 2006. The interim report of Meda in 2008 informs that Optivar has a total sales of SEK 80 million in which USD 9 million is from US market. Court proceedings against Sun for Optivar are scheduled to start on 20 July 2009.

The Sun Pharma spokesperson refused to comment on the latest development, as the issue is under the consideration of the court.