The maker of the EpiPen is tanking after it was called out for hiking the drug's price by over 500%

Mylan Pharmaceuticals, the company that makes the emergency allergy medication EpiPen, is under pressure.

The drugmaker’s stock is down 4% Tuesday. That’s after Sens. Chuck Grassley of Iowa and Richard Blumenthal of Connecticut wrote separate letters asking for more information from the company about how the drug’s price has increased more than 500% since 2009.

In response to questions about its high list price, Mylan noted in an email to Business Insider that about 80% of people with commercial insurance who also used a “My EpiPen Savings Card” received the device for $0, though they did note that changing insurance plans with higher deductibles could be adding to the price pressure.

“This shift has presented new challenges for consumers, and they are bearing more of the cost. This change to the industry is not an easy challenge to address, but we recognise the need and are committed to working with customers and payors to find solutions to meet the needs of the patients and families we serve.”

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