US-based Forest Laboratories has sued leading Indian drug firms, Lupin Ltd, Orchid Chemicals & Pharmaceuticals Ltd and Wockhardt Ltd, for alleged infringement of Forest?s Alzheimer?s drug patent.

In a suit filed in the US District Court of Delaware, along with its partner, Merz Pharma GmbH, Forest Labs argued that the generic drugs to be launched by the firms will infringe the ?703 US patent, granted to the company for Namenda, its leading drug for treating Alzheimer?s disease. The other defendants named in the lawsuits include Barr Laboratories Inc, Cobalt Laboratories Inc, Teva Pharmaceuticals USA Inc, and Upsher-Smith Laboratories Inc. The ?703 patent expires in April 2010. Namenda generated sales of $192.9 million during the fiscal 2008-second quarter.

Forest has applied for a patent term extension which, if granted, would extend the ?703 patent until September 2013. In its statement, Forest Labs said that it had received notification from several companies that they had filed Abbreviated New Drug Applications (ANDA) with paragraph IV certifications to obtain approval to market generic versions of Namenda.

Viewing the windfall from the 180-day marketing exclusivity that the company can enjoy if it wins the patent litigation, more Indian firms are filing paragraph IV ANDAs. Once the paragraph IV ANDAs are filed with the US FDA by generic firms, the patent holder must challenge the ANDA in the court, accusing the ANDA will infringe the patent granted to the innovator company.

During December last year, Astrazeneca Pharmaceuticals sued Aurobindo pharma and Sun Pharma in various US courts, alleging their paragraph IV ANDA to manufacture a generic version of Astrazeneca?s Crestor, used to treat high cholesterol, will infringe the patent.

Crestor recorded sales of more than $2 billion in 2006. In December first week, in a similar move, Glenmark Pharmaceuticals Inc. was sued by Sanofi-Aventis, following a paragraph IV ANDA filing by Glenmark’s to manufacture a generic version of plaintiffs’ Tarka, drug for hypertension.

In the same week, US-based Abbott Laboratories filed suit against Zydus Pharmaceuticals following Zydus? filing of para IV ANDA to manufacture a generic version of Abbott?s Depakote, which recorded sales of $1.23 billion in 2006.