Six Pacific trading partners are resisting a U.S. push to set rules that would protect patented next-generation medicines from competition from generic drugs for eight years and are insisting on a shorter period of five years as part of a sweeping trade pact, two sources close to the negotiations said on Friday. Ministers from the 12 countries negotiating the Trans-Pacific Partnership (TPP) entered a third day of talks in Atlanta still deadlocked over the treatment of biologic drugs, next-generation drugs which are made from living cells and used to treat cancer and other diseases.