WASHINGTON (AP) — A Democratic senator is seeking marketing information, sales records and studies from manufacturers of the top-selling opioid products in the United States to determine whether drugmakers have contributed to an overuse of the pain killers.

Sen. Claire McCaskill of Missouri said that sales of prescription opioids have quadrupled since 1999, taking a financial toll on the government and a deadly toll on thousands of consumers.

McCaskill said previous government and media reports show an industry not focused on preventing abuse but on fostering addiction. She is investigating whether such practices continue today.

Some of the records she is asking for from the five companies include the sales rep expenses for entertaining physicians, payments made to health care advocacy groups, as well as marketing and business plans.

"We have an obligation to everyone devastated by this epidemic to find answers," McCaskill said in a prepared statement issued Tuesday. "All of this didn't happen overnight. It happened one prescription and marketing program at a time."

More than 52,000 people died of drug overdoses in 2015, and roughly two-thirds of them had used prescription opioids like OxyContin or Vicodin or illegal drugs like heroin, according to the Centers for Disease Control and Prevention. Those overdoses have jumped 33 percent in the past five years alone, with some states reporting the death toll had doubled or more.

Last September, The Associated Press and Center for Public Integrity published an investigation outlining how makers of prescription painkillers have adopted a 50-state strategy that includes hundreds of lobbyists and millions in campaign contributions to help kill or weaken measures aimed at stemming the tide of prescription opioids.

The industry and its allies spent more than $880 million nationwide on lobbying and campaign contributions from 2006 through 2015 — more than 200 times what those advocating for stricter policies spent and eight times more than the influential gun lobby recorded for similar activities during that same period, the investigation found.

McCaskill is the ranking Democratic lawmaker on the Senate Committee on Homeland Security and Governmental Affairs. The Republican chairman, Sen. Ron Johnson, did not sign the letter seeking the information from the drug manufacturers, and an aide said Republicans weren't given time to join the investigation.

Brittni Palke, spokeswoman for the committee, said McCaskill waited until the last minute to notify Johnson of the probe. She said Johnson was disappointed by McCaskill's decision to "get headlines instead of results."

"Contrary to the committee's longstanding bipartisan traditions, Senator McCaskill chose to make her requests unilaterally despite widespread interest in coming together to address the root causes of America's opioid addiction," Palke said.