As many as half the patients who were prescribed potent fentanyl painkillers designed for people battling cancer should not have received the drug from doctors, according to a study released Tuesday that sheds light on opioid oversight.

Among the chief findings is that the U.S. Food and Drug Administration and drug manufacturers failed to properly regulate the painkiller despite safeguards adopted eight years ago, according to the report. The findings are based on 4,877 pages of documents obtained by public records requests filed by researchers from Johns Hopkins and Yale universities.

Although the FDA has maintained a monitoring program since 2011 to track such medications, the study says the FDA and fentanyl makers did not take action when evidence arose about inappropriate prescriptions.

Drug manufacturers did not report a single instance in which a physician incorrectly prescribed the drug, the report says.

“The million-dollar question is, how on earth did such high rates of unsafe use occur when these products were subject to one of the most restrictive distribution systems that the FDA and manufacturers have?” said Caleb Alexander, a professor of epidemiology at the Johns Hopkins Bloomberg School of Public Health, which helped lead the study.

The findings – published in the Journal of the American Medical Association – come amid a raging national opioid crisis. More than 47,000 people in the USA died from opioids in 2017, making the odds of dying from an opioid overdose greater than dying by car crash. Over-prescribing contributed to the epidemic.

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At issue is a type of fentanyl called Transmucosal Immediate-Release Fentanyl, or TIRF, which is 100 times more powerful than morphine.

The drug, which is taken by either sublingual and buccal tablets, lozenges or sprays, is designed primarily for cancer patients with “breakthrough pain” who are already tolerant to opioids.

“These are not your typical products,” Alexander said in an interview. “The risks of these products are not typical risks. If these products are used among patients who are not already what we call ‘opioid-tolerant’ and are on around-the-clock opioids, they can be fatal. They can kill you.”

The study reviewed documents from 2012 to 2017 that are part of the FDA monitoring system for TIRFs. Records were obtained through the federal Freedom of Information Act with help from Yale Law School’s Collaboration for Research Integrity and Transparency.

In a statement to USA TODAY, the FDA said the agency “shares the concerns” about how TIRF products are used and whether the monitoring program works as intended.

“These products are medically important for a small group of patients who are opioid-tolerant but also pose serious risks,” the statement said. “That’s why the agency has sought to ensure that the TIRF (monitoring) program is achieving its public health goal of assuring safe use and mitigating the risks of misuse, abuse, addiction, overdose, and complications due to medication errors.”

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The statement said the FDA has been “actively assessing” the recommendations of an advisory committee and will soon share planned next steps, including modifications to the monitoring program.

The data in the study include health insurance claims, which the FDA started to review in 2014 as part of the monitoring process. An initial set of insurance reports showed 51 percent of patients receiving TIRFs – 12,916 of 25,322 patients – were not opioid-tolerant, therefore should not have received the painkiller.

The same assessment found the FDA and drug companies had not reported any case of a physician prescribing a TIRF to a patient who is not tolerant of opioids, nor had they reported any examples of prescribers being disenrolled, the report says.

A subsequent analysis of health insurance claims, conducted in 2016, found that 34.6 percent to 55.4 percent of TIRF patients lacked opioid tolerance, depending on which TIRF drug was prescribed.

This was the case even though surveys, detailed in the same monitoring system, indicate that the majority of pharmacists, prescribers and patients were aware that TIRFs are supposed to be prescribed to patients who have developed a tolerance for opioids.

“Despite increasing evidence that the program was not achieving its stated goals, no substantive changes to the program were made by TIRF manufacturers or the FDA to address these shortcomings,” the study says.

In recognition that the monitoring system did not meet the agency’s goals, the FDA requested further analyses of opioid tolerance among patients receiving TIRFs after the program’s fifth-year evaluation in 2017.

The next year, the FDA held a public advisory committee meeting in August 2018 to examine the TIRF monitoring program.