The cost of EpiPens — the go-to drug injectors for children and adults suffering from severe allergic reactions — has skyrocketed in the past several years, leaving families scrambling in a market that offers few alternatives.

Members of Congress are demanding more information from the drug’s manufacturer, Mylan, on why the cost of a two-pen set, which parents and allergists said can be the deciding factor in whether a child survives a reaction, is now listed at more than $600. In 2007, when Mylan took over rights to EpiPen, a pair of syringes cost $93.88.

“It’s not like this is a luxury product,” said Teri Tonna, of Massapequa, whose 12-year-old daughter requires the pen for her allergies to dairy, eggs and tree nuts. “It literally means the difference between life and death.”

EpiPen is the most widely prescribed auto-injector on the market, found in schools, offices and first aid kits across the country. It’s used to treat anaphylactic allergic reactions, which constrain breathing, among other symptoms, and is designed to allow sufferers and those around them to stop the reaction with epinephrine, also known as adrenaline.

In a statement, Mylan did not give an explanation for the price increase but defended the cost, saying prices had always been rising. Families were feeling an increased financial burden, they said, due to changes in the insurance industry and high deductible insurance plans.

Officials also noted that the company offers a $100 coupon online.

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“EpiPen is a first-line therapy. It can be lifesaving, so it needs to be available to the patient at an affordable price,” said Dr. Susan Schuval, chief of pediatric allergy and immunology at Stony Brook University Hospital.

Families have the choice to use another, similar injector, but nothing quite matches the ubiquity and ease of the EpiPen, said Dr. Sherry Farzan, a specialist in allergy and immunology at Northwell Health in Great Neck. The drug itself is inexpensive, but the cost of the applicator ranges.

Competitor Auvi-Q was pulled off the market in 2015 amid concerns about malfunctioning devices, and Adrenaclick, another option, is more difficult to apply, Farzan said.

Last year, more than 3.6 million U.S. prescriptions for two-packs of EpiPens were filled, according to data firm IMS Health.

Tonna said her family has relied on EpiPen for more than a decade. Like many families, they have multiple sets — up to three for a total of six pens — to cover all scenarios when their daughter might come into contact with an allergen, and using an alternative made Tonna uneasy.

“I only found recently that there’s a generic company, but I don’t know if I would trust that,” she said. “It can’t not work if you need it.”

At Stony Brook, Schuval said EpiPens are the standard prescription for anyone diagnosed with a severe allergy. The cost has not yet prevented her patients from getting the injector, she said.

“They usually can get a reduction in their copay, but for patients without insurance, it can be an issue,” Schuval said. “We’re expecting it to be a big problem in the future.”

Before Tonna met her deductible, she said pharmacies were quoting her $600 for a single set, a trend she began noticing last year.

The copay coupon helps, but only when it works, like last week, when she was able to get the cost down to $100 for her daughter’s newest set.

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“I don’t know what people do that have a kid with food allergies and don’t have insurance,” she said. “It’s frustrating. You just have to suck it up and pay the price.”