CAMBRIDGE, Mass., March 22, 2013 (GLOBE NEWSWIRE) -- Idenix Pharmaceuticals, Inc. (Nasdaq:IDIX), a biopharmaceutical company engaged in the discovery and development of drugs for the treatment of human viral diseases, today announced that the United States Patent and Trademark Office Patent Trial and Appeal Board (USPTO) issued a decision in the first phase of the ongoing interference concerning one of the Company's patent applications (U.S. Patent Application 12/131,868) and an issued patent ( U.S. Patent 7,429,572) owned by Gilead Pharmasset LLC ("Gilead") that covers certain 2'-methyl- 2'-fluoro nucleoside compounds useful in the treatment of the hepatitis C virus. An interference is an adversarial proceeding declared by the USPTO when a party has a U.S. patent application that covers the same invention as another patent application or issued patent to determine priority of invention in the United States. An interference proceeding is divided into two stages. The first phase determines the application filing dates each party will have benefit of for the interfering subject matter. The party with the benefit of the earliest application filing date is deemed the 'senior party' and the party with the later date is deemed the 'junior party'. The second phase determines who was first to invent. The party who is deemed first to invent prevails in the interference proceeding. Today the USPTO issued a decision whereby Idenix was determined to have a later application filing date than Gilead. Therefore Idenix was determined to be the 'junior party' and Gilead the 'senior party' in the interference. The second phase of the interference is expected to commence in the second quarter of 2013 and, as noted above, will determine which party was first to invent. The decision that Idenix is the junior party does not determine which party will be deemed first to invent and ultimately prevail in the interference.