After 2010, when oxycodone - a high-dose opioid painkiller sold as OxyContin - was switched by its manufacturer to a new abuse-deterrent formulation, overdose rates fell substantially, researchers have found.

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In addition to potential misuse by people receiving the original prescription, opioid painkillers may be diverted to illicit users.

The formulation change also saw a drop in the levels of dispensing, and the lower opioid overdose and prescribing levels also correlated with the withdrawal from the market of another narcotic drug in the same year, propoxyphene.

OxyContin is an extended-release formulation to deliver its higher painkilling dose in a more controlled way, but misuse of this opioid for a quicker "high" had been possible by crushing or dissolving the medication to bypass this design. The new formulation, however, is resistant to this abuse strategy.

Propoxyphene (Darvon) was withdrawn from the US market in 2010 because of data about its cardiac side-effects. First approved for sale as an analgesic in 1957, it soon became prone to misuse - and the authors cite that, by 1977, propoxyphene was the "second-leading agent in prescription drug-induced deaths."

The authors of the study in JAMA Internal Medicine describe the reduction in dispensing following these two pharmaceutical industry changes in 2010:

"The introduction of abuse-deterrent OxyContin and withdrawal of propoxyphene at the end of 2010 were associated with sudden, substantial and sustained decreases in prescription opioid dispensing.

The estimated decrease in opioid dispensing at 2 years would be enough to supply 5 mg of oxycodone each day of the fourth quarter of 2012 to 5% of the population."

Fall in level of morphine-equivalent amounts dispensed

The researchers analyzed the prescribing of opioids to commercial health plan members across the US to reach the estimated average level of morphine-equivalent dose (MED).

For all opioids combined, between 2003 and the third quarter of 2010, the dispensing rate rose from 95 mg to 163 mg MED per plan beneficiary.

Immediately following the interventions, the dispensing rate dropped by 14.8 mg MED per member, and a downward trend then continued to buck predictions, leading to the rate in the last quarter of 2012 being estimated at 139 mg MED per member, down from the 163 mg peak.

Against the predicted trend of opioid prescriptions, this represented a 19% decrease following the 2010 changes. Further, the estimated rate of overdose also dropped - by 20%.

The prescribing data, drawn from over 31 million insured members, were analyzed by Dr. Marc Larochelle, of the Harvard Medical School and Boston University School of Medicine, and coauthors. They conclude:

"Our results have significant implications for policymakers and health care professionals grappling with the epidemic of opioid abuse and overdose. Changes imposed through regulatory mandates or voluntary company actions may be a viable approach to stemming prescription abuse."

A note of caution is made with this call, however, to reduce opioid supply without harming access to the therapeutic benefit of painkilling treatments.

The authors also warn that interventions at the supply end do not cure the present demand problem, even though it "might decrease new-onset addiction in the future."

Alongside the opioid findings, the authors found that heroin overdose, conversely, increased by 23% in the study period. The authors note:

"Regardless of the mediating mechanism, a transition from prescription opioid to heroin abuse has been well documented and further efforts are needed to improve identification and treatment of these individuals."