The Senate Aging Committee has asked pharmaceutical giant Pfizer for information about soaring prices for the generic drug naloxone, used to reverse the effects of an opioid overdose.
The drug's price rose from $45 for a set of 10 vials in 2009 to $263.88 in early 2014—an increase of almost 600 percent, before settling to $189.96, CNBC reported in September.
"Drug overdoses are now the leading cause of accidental death in the United States, many related to misuse or abuse of prescription opioids," Senators Susan Collins and Claire McCaskill wrote in a letter to Pfizer CEO Ian Read dated Nov. 28, a copy of which was obtained by CNBC.
Pfizer gained naloxone when it acquired Hospira for $17 billion in 2015. The senators said they'd already received 2015-2016 pricing information on the drug from Pfizer, in response to an earlier letter.
"Explain, in detail, the number and amount of price increases and decreases taken by Hospira between 2009 and 2014 for naloxone," the senators wrote.
They also asked for details on how Hospira came to the decision to raise the price, as well as how much the increases contributed to research and development into improving the product, and whether any issues of patient access arose.
In response to an inquiry from CNBC, Pfizer defended its pricing, saying the drug's cost was "priced responsibly" in a statement.
"From the time Naloxone entered our portfolio...our focus has been on providing access to this life saving treatment and we believe it is priced responsibly at a wholesale acquisition cost (WAC) price of $15.83 per dose for the single dose vial, and $11.87 per dose for the multidose vial (10 doses in a vial)," the statement read.
"Pfizer's Naloxone Access Program includes a donation of up to 1 million doses of Naloxone over four years and $1 million in opioid overdose grants to several states."
Pfizer isn't the only maker of naloxone. Other formulations and delivery systems are on the market, including an auto injector called Evzio from private manufacturer Kaleo that costs almost $4,000 for two doses.
Collins and McCaskill wrote letters to five manufacturers in June inquiring about price increases.