The Mumbai-based Sun Pharmaceuticals has agreed to stop manufacturing and marketing of its generic version of Namenda (memantine hydrochloride), the lucrative Alzheimer’s drug patented by Forest Laboratories with the resolving of the dispute between the two firms at the US District Court for the District of Delaware.

According to reports, Sun Pharma has agreed to abstain from marketing or manufacturing 5 mg or 10 mg tablets during the life of the US Patent No. 5,061,703 ('703), entitled 'Adamantane Derivatives in the Prevention and Treatment of Cerebral Ischemia', unless all asserted claims of the patent have been found to be invalid.

On the basis of this, the US District Judge Gregory M Sleet of the US District Court signed off on a stipulation and order resolving the dispute dismissing all claims and counterclaims without prejudice in the case. Though denied on any infringement of the '703 earlier, Sun Pharma lately admitted that its filing of an Abbreviated New Drug Application (ANDA) with the FDA constituted 'technical act of infringement'.

The court order comes as a latest development in a number of patent lawsuits filed by Forest Lab and its partner Merz Pharma GmbH & Co. KGaA, against various pharma companies including the leading Indian drug firms, Lupin Ltd, Orchid Chemicals & Pharmaceuticals Ltd and Wockhardt Ltd along with companies like Barr Laboratories Inc, Cobalt Laboratories Inc, Teva Pharmaceuticals USA Inc, and Upsher-Smith Laboratories Inc.

Even as the ‘703 patent was scheduled to expire in April 2010, the patent validity is now extended for another five years by the US Patent and Trademark Office. According to the decision, Forest Lab and its partner can hold the patent rights till April, 2015.

Namenda, which is one of the major drugs in the Alzheimer’s disease treatment, has recorded a sales growth of approximately 12 per cent over the US$ 949.3 million in fiscal 2009. Further, the Q3 results announced by Forest on October 20, 2009, reports that the sales of Namenda jumped 11.9 per cent to US$ 275.3 million, beating estimates of US$ 263.7 million.