(Reuters) - U.S. Food and Drug Administration (FDA) scientists on Monday expressed concern that Intellipharmaceutics International Inc had failed to provide adequate data on the abuse potential of its long-acting opioid painkiller.

Opioids are considered the gold standard in treating pain that persists despite other forms of therapy, but the rising wave of abuse is taking a toll on the U.S. healthcare system.

Health regulators have implemented a slew of measures of limit their supply, in particular requiring drugmakers such as Intellipharmaceutics to prove their painkillers discourage abuse.

Toronto-based Intellipharma’s painkiller, Rexista, has been developed as a unique abuse-deterrent version of Purdue Pharma’s often-abused blockbuster OxyContin, which already has tamper-resistant properties.

Most notably, Rexista contains a blue dye that is emitted if the tablet is manipulated, which could help identify abusers. The drug has also shown bioequivalence to OxyContin, which means that if approved, it could be used interchangeably with OxyContin.

Long-acting opioids contain high doses of narcotics designed to be released over time. If crushed pills are snorted or injected, they release their full dose all at once, making them dangerous and valuable for addicts.

In a preliminary review, FDA staffers said Intellipharma had not submitted abuse-liability study data as part of its application to market Rexista in the United States. bit.ly/2eHJpSH

“It basically comes down to a philosophical difference with the FDA,” Intellipharma’s finance chief Domenic Della Penna said in an interview.

“If you are bioequivalent to something, why do you need to do all these extra studies?”

Penna noted that Rexista was relatively harder to abuse via the popular method of injection, adding that other studies would follow.

FDA staff noted that Rexista was easier to crush than OxyContin, but said it was similar to OxyContin or was less likely to be manipulated for abuse using a syringe.

Agency scientists also concluded Rexista was less likely to vaporize if manipulated for abuse via inhalation, and that it was not easy to separate the blue dye and nasal irritant from the drug.

The FDA’s report comes two days ahead of a meeting of independent advisers who will make recommendations on Rexista. The regulator is expected to decide on Rexista’s approval by Sept. 25.

However, since Purdue has sued Intellipharma, claiming patent infringement, the drug’s final approval is subject to the outcome of the lawsuit.

Intellipharma’s U.S.-listed shares were down 11.8 percent at $2.37 in midday trading.