NEW YORK (AP) — Sales growth of prescription drugs in the U.S. slowed for the second straight year, with the economic downturn playing a key role, according to IMS Health Inc. Norwalk, Conn.-based IMS, which conducts health care market research, cited lower demand for less-expensive generic drugs, lagging new product sales, and reduced consumer demand. Sales rose just 1.3 percent to $291 billion in 2008, falling within the company's prior outlook of 1 percent to 2 percent growth. In 2007, U.S. sales rose 3.8 percent to $286.5 billion, while they gained 8 percent in 2006. Anti-psychotic drugs were the lead sales drivers, followed by cholesterol drugs and treatments for heartburn and related conditions. New York-based Pfizer Inc.'s cholesterol pill Lipitor retained its spot as the drug with the highest sales, followed by the heartburn treatment Nexium, made by British drug developer AstraZeneca PLC. Meanwhile, IMS said dispensed prescription volume rose 0.9 percent, with cholesterol drugs being the most widely dispensed.