Merck, the original patent holder of finasteride, has now filed a lawsuit against Dr Reddy's Lab in the United States District Court for the District of Delaware, alleging that the latter has infringed the patent rights 817 and 957 for the drug molecule finasteride.

The European pharma major filed the patent infringement case against DRL on September 29, 2004.

Dr Reddy's Laboratories had filed an Abbreviated New Drug Application (ANDA) with the United States Food and Drug Administration for finasteride tablets 1 mg with a Paragraph IV certification on three of the four Orange Book patents listed for the drug, in June 2002.

Though DRL notified Merck on the ANDA filing in September 2002, the latter did not file a lawsuit within the 45-day period under the Hatch-Waxman Act.

Finasteride tablets 1 mg is the generic version of Merck's Propecia with annual brand sales in the United States of approximately $ 112 million.