(Adds background on drug pricing)
NEW YORK, Aug 17 (Reuters) - U.S. House Democrats said on Thursday they were launching an investigation into why prices for Multiple Sclerosis (MS) treatments have nearly quadrupled since 2004, and they sent letters requesting information from seven drugmakers.
U.S. Representatives Elijah Cummings and Peter Welch sent the letters to Bayer AG, Biogen Inc, EMD Serono, Novartis AG, Roche Holding AG, Sanofi SA, and Teva Pharmaceutical Industries Inc .
The lawmakers on the U.S. House Committee on Oversight and Government Reform said in the letters that they were looking to determine whether drug companies were raising prices for MS drugs in lockstep with their competitors.
The letters said that the average cost of MS therapy rose to more than $60,000 in 2015 from $16,050 in 2004.
Drugmakers have faced a global pushback from regulators and lawmakers about high prices.
President Donald Trump has said the companies are "getting away with murder" and has pledged to lower the cost of prescription drugs. He met with Representative Cummings to discuss the issue in March.
Previous congressional investigations and hearings into drug pricing practices have had far-reaching effects. Mylan NV sharply reduced the cost of EpiPen after the Oversight Committee began looking into the increases that drove the list price of the life saving allergy treatment to around $600 a pair.
Valeant Pharmaceuticals International and Turing Pharmaceuticals have also faced congressional pressure over high prices.
Sanofi and Novartis did not immediately have a comment on the probe. Bayer, Biogen, EMD Serono, Roche, and Teva Pharmaceutical Industries Inc could not immediately be reached for comment. (Reporting by Michael Erman; editing by David Gregorio and Andrew Hay)