Pacific Rim trade ministers neared the final spurt of negotiations on an ambitious free trade pact on Thursday, but differences over farm exports and monopoly periods for next-generation drugs kept them short of an elusive final deal. Ministers from the 12 countries negotiating the Trans-Pacific Partnership (TPP), which would cut trade barriers and set common standards for 40 percent of the world economy, are meeting in Hawaii to try to hammer out a deal. The United States is pushing for 12 years but Australia and other countries worried about the impact on medicine prices want five.