Forest Laboratories has filed lawsuits against a number of companies who are planning to market generic versions of the Alzheimer’s disease drug Namenda.

The firm, along with Germany’s Merz Pharma (which licensed the drug to Forest in 2001) says that Namenda (memantine) patent infringement lawsuits have been issued against Teva, Barr Laboratories and Cobalt, plus the Indian drugmakers Lupin, Orchid and Wockhardt, among others. Forest said it had started legal proceedings once it had received notification from several companies that they had filed Abbreviated New Drug Applications in the USA with Paragraph IV certifications to obtain approval for their copycat versions of Namenda.

Forest, which filed the suit in the US District Court in Delaware, said its Namenda patent expires in April 2010, and it has applied for an extension which, if granted, would give coverage up to September 2013. The drug, which is an N-methyl-D-aspartate receptor antagonist for the treatment of moderate and severe Alzheimer's disease, is a major earner for Forest and third-quarter 2007 sales reached $192.9 million, an increase of 24%.

Keeping those sales up is vital for Forest as its flagship antidepressant Lexapro (escitalopram oxalate), which is licensed from Denmark’s Lundbeck, is scheduled to come off-patent in the USA in 2012.