The head of a pharmaceutical company, who partnered with the Clinton Foundation, has increased the price of an auto-injector used to treat opioid overdoses by 680 percent over the course of three years.

Spencer Williamson, the president and chief executive officer of the Richmond, Virginia-based Kaleo Pharmaceuticals, is under fire after the price of a two-pack of Evzio, a device that treats life-threatening opioid overdoses, skyrocketed from $690 in 2014 to $4,500 today.

Thirty-one Democratic senators are now demanding answers on the price hike.

"We are deeply concerned about reports that Kaleo dramatically increased the cost of its naloxone injector device, Evzio, an FDA approved medication used for the emergency treatment of an opioid overdoes – from $690 for a two pack in 2014 to $4,500 today," the letter sent from the senators to Williamson said.

"This drug is now in the hands of first responders and families struggling with substance use disorder across the country. It is particularly needed in rural areas where access to life-saving emergency services can be limited. Such a steep rise in the cost of this drug threatens to price-out families and communities that depend on naloxone to save lives."

The senators ask Williamson to detail the pricing structure of Evzio and to provide documentation as to why the company changed its pricing structure. In addition, the lawmakers seek the total amount that Evzio has received in reimbursements over the last 12 months, among other demands.

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