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U.S. Senators are scrutinizing the rising price of EpiPens following a public outcry over the 400 percent price hike since 2008.

On Monday, Senator Charles Grassley of Iowa, chairman of the Senate Judiciary Committee, sent a letter to Heather Bresch, chief executive officer of Mylan, the maker of EpiPens. The letter, which cited earlier NBC News reporting, said he was "concerned that the substantial price increase could limit access to a much-needed medication" and requested additional information on the price increases.

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Separately, Connecticut Senator Richard Blumenthal urged Mylan to reduce the price of EpiPens.

"I demand that Mylan take immediate action to lower the price of EpiPen’s for all Americans that rely on this product for their health and safety," he wrote in a letter to Bresch, citing hearing from dozens of concerned families, school nurses and first responders.

EpiPen average wholesale price chart, 2007-2016. Ben Popken / NBC News

They join Senator Amy Klobuchar of Minnesota, the top Democrat on the Judiciary committee's antitrust subcommittee, who called for a hearing to investigate "the enormous increase in the price of EpiPens." The Senator on Sunday, who said her daughter uses an EpiPen, also sent a letter to the FTC requesting an investigation into Mylan's trade practices.

EpiPens are a marker-sized device that are jammed into a thigh to deliver epinephrine. The medicine is used to stop the potentially fatal anaphylactic shock that comes with a severe allergic reaction.

"Although the antitrust laws do not prohibit price gouging, regardless of how unseemly it may be, they do prohibit the use of unreasonable restraints of trade to facilitate or protect a price increase," wrote Klobuchar.

"The FTC should investigate whether Mylan Pharmaceuticals engaged in activity, such as using incentives or exclusionary contracts with insurers, distributors, or pharmacies, to deny an alternative product access to the market."

Mylan did not immediately respond to a request for comment on the new letters. In an earlier statement the company said the "wholesale price has changed over time to better reflect important product features and the value the product provides" and that "ensuring access to epinephrine — the only first-line treatment — is a core part of our mission."