First came Martin Shkreli, the brash young pharmaceutical entrepreneur who raised the price for an AIDS treatment by 5,000 percent. Then, Heather Bresch, the CEO of Mylan, who oversaw the price hike for its signature Epi-Pen to more than $600 for a twin-pack, though its active ingredient costs pennies by comparison.

Now a small Virginia company called Kaleo is joining their ranks. It makes an injector device that is suddenly in demand because of the nation’s epidemic use of opioids, a class of drugs that includes heavy painkillers and heroin.

Called Evzio, it is used to deliver naloxone, a life-saving antidote to overdoses of opioids. And as demand for Kaleo’s product has grown, the privately held firm has raised its twin-pack price to $4,500, from $690 in 2014. Founded by twin brothers Eric and Evan Edwards, 36, the company first sought to develop an Epi-Pen competitor, thanks to their own food allergies. Now, they’ve taken that model and marketed it for a major public health crisis. It’s another auto-injector that delivers an inexpensive medicine.

And the cost of generic, injectable naloxone – which has been on the market since 1971 – has been climbing. A 10-mililiter vial sold by one of the dominant vendors costs close to $150, more than double its price from even a few years ago, and far beyond the production costs of the naloxone chemical, researchers say. The other common injectable, which comes in a smaller but more potent dose, costs closer to $40, still about double its 2009 cost.

U.S. Senator Claire McCaskill on Thursday asked Kaleo Pharmaceuticals to justify the more than 550 percent surge in the price of its device to treat painkiller overdoses, becoming the second senator to question Evzio’s $4,500 price tag.  Senator Amy Klobuchar sent Kaleo a letter earlier this month, voicing similar concerns.

Evzio contains the overdose-reversing drug naloxone and can be used in emergencies by people without medical training. Privately held Kaleo has raised the price of a twin-pack to $4,500, from $690 in 2014, according to a Kaiser Health News report.

The concerns over Evzio’s price comes at a time when pharmaceutical companies are facing intense scrutiny over “price-gouging”, and as lawmakers struggle with the epidemic of opioid abuse.

“At a time when Congress has worked to expand access to naloxone products and to assist state and local communities to equip first responders with this life-saving drug, this startling price hike is very concerning,” McCaskill said in a letter to Kaleo Chief Executive Spencer Williamson. The letter, which was signed by 30 U.S. senators, asked Kaleo for information on Evzio’s price structure and why the company chose to adjust prices.

“We received the letter from the Senators and are in communication with them to ensure all questions are addressed,” Williamson told Reuters in an e-mailed statement.

“There’s absolutely nothing that warrants them charging what they’re charging,” said Leo Beletsky, an associate professor of law and health sciences at Northeastern University in Boston.