More than 30 U.S. senators have asked Kaleo Pharmaceuticals to explain why it raised the price of its opioid overdose reversal medication by nearly $4,000. Reports indicate the company increased the price of Evzio from $690 for a twin-pack to $4,500 today. In a letter to Kaleo CEO Spencer Williamson, the senators said the price increase is "very concerning." They wrote, "We are concerned about the impact the high list price may have for those who do not qualify for the (discount program) and for state and local entities who hope to purchase large quantities of your product." The senators asked Kaleo to provide information about its pricing structure for Evzio since it received FDA approval and how many Evzio devices are set aside for the company's donation program. In a statement, Williamson acknowledged he received the letter and is communicating with the senators who signed it to "ensure all questions are addressed."