** Shares of pharmaceutical companies fell in afternoon trading on Thurs, with an index of pharmaceutical companies .DRG down 2.4%, after the White House said U.S. President Donald Trump has sent letters to the chief executives of 17 major cos, urging them to lower the cost of prescription drugs for Americans

** Shares of Eli Lilly LLY.N were last down 2.8%, while Merck & Co MRK.N was down 3.7%. Both were among companies to which Trump sent letters. Also sent letters were Regeneron REGN.O, down 1.95%; Johnson & Johnson JNJ.N, down 1.4%; as well as Sanofi SASY.PA and AstraZeneca AZN.L and others

** Eli Lilly and Merck were among companies weighing on the S&P 500 .SPX, which was down 0.11%

** The S&P 500 healthcare sector .SPXHC was down 2.68% on Thurs, the most of any of the 11 major sectors

(Reporting by Caroline Valetkevitch)

((caroline.valetkevitch@tr.com))