In her decision, seen by AFP, judge Colleen McMahon said the federal judge who approved the pharmaceutical company’s bankruptcy plan in September did not have authority to prevent future lawsuits against members of the Sackler family, except in cases of intentional misconduct.

Forty-three US states had approved the plan but the justice department and a handful of other states challenged it.

They argued that it denied victims the right to sue the company.

Under the settlement Purdue Pharma, the manufacturer of OxyContin, would be dissolved and the Sackler families that founded and profited from the company would have to pay US$4.5 billion.

But they could not be taken to court again over the drug.

The opioid addiction crisis caused more than 500,000 overdose deaths in the US over the past 20 years.

Facing an avalanche of litigation, Purdue last year pled guilty to three criminal charges over its aggressive drive to push sales of OxyContin, a highly addictive prescription painkiller.

Under the terms of the deal, the company would be sold by 2024 to be replaced by a new entity managed by a trust, and its involvement in selling opioid products would be restricted.

Purdue also would be required to create a repository for tens of millions of documents detailing its sales and marketing practices.