FILE - In this July 8, 2016, file photo, a pharmacist holds a package of EpiPens epinephrine auto-injector, a Mylan product, in Sacramento, Calif. Mylan said it will make available a generic version of its EpiPen, as criticism mounts over the price of its injectable medicine. (AP Photo/Rich Pedroncelli, File)

FILE - In this July 8, 2016, file photo, a pharmacist holds a package of EpiPens epinephrine auto-injector, a Mylan product, in Sacramento, Calif. Mylan said it will make available a generic version of its EpiPen, as criticism mounts over the price of its injectable medicine. (AP Photo/Rich Pedroncelli, File)

WASHINGTON (AP) — In a sign of growing concern in Congress, 20 Democratic senators are demanding answers about steep price hikes for the life-saving EpiPen injector device.

The senators said in a letter Tuesday that price hikes of more than 500 percent have jeopardized access to emergency allergy shots for many Americans. The letter was addressed to Heather Bresch, CEO of the pharmaceutical company that makes the devices, Mylan N.V.

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Bresch is the daughter of Sen. Joe Manchin, D-W.Va. Manchin did not sign the letter.

Mylan has responded to the public outcry over the price hikes by expanding programs to make EpiPens more affordable and promising a cheaper, generic version. But Massachusetts Sen. Elizabeth Warren and other senators said the generic device still costs $300, three times more than the branded EpiPen did in 2007.

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“Some Americans who are unable to afford this cost increase have resorted to carrying expired EpiPens — or carry no EpiPens at all,” Warren and other senators said in an eight-page letter. The lawmakers asked Mylan to answer detailed questions by Sept. 12.

The senators said Mylan’s near monopoly on the epinephrine auto-injector market has allowed it to increase prices well beyond increases in manufacturing costs.

Mylan has not reduced the $608 list price for a pair of EpiPen auto injectors or explained why it boosted prices by 500 percent since 2007.

EpiPens are used in emergencies to stop potentially fatal allergic reactions to insect bites and stings, and foods like nuts and eggs. People usually keep multiple EpiPens handy at home, school or work, but the syringes, prefilled with the hormone epinephrine, expire after a year.

The price hike, which hit just as parents and students were preparing for a new school year, has led to an election-year uproar amid widespread concerns about high drug prices. A chorus of politicians, consumer groups and parents has been calling for hearings and investigations of EpiPen pricing, along with action by the Food and Drug Administration to speed approvals of rival products.

There’s currently little competition for EpiPen. Rival Adrenaclick carries a list price of $461, and there’s a generic version, but doctors typically prescribe EpiPen, originally launched in 1987, because it’s so well-known.

Last week, Mylan offered more financial aid to patients getting EpiPens, including coupon cards covering up to $300 off patient copayments, triple the $100 discounts previously offered. Coupon cards are a standard pharmaceutical industry strategy, one that leaves employers and taxpayers still footing at least two-thirds of a big bill — and everyone facing eventual higher insurance premiums.

A generic competitor was expected in 2015 but has been delayed.

On Monday, leaders of the House Oversight and Government Reform Committee wrote to Bresch, requesting information about Mylan’s revenues from EpiPens since 2007, manufacturing costs and how much Mylan receives from federal health care programs.

Leaders of the House Energy and Commerce Committee sent a letter to FDA Commissioner Dr. Robert Califf about the lack of competition for auto-injection devices.

“EpiPens are a critical and often only option for saving kids from the brink of death during severe allergic reactions. And the soaring costs that patients are now facing for Epi-Pen Auto-Injectors is cause for alarm,” said Rep. Fred Upton, R-Mich., the panel’s chairman.

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