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Experimental opioid reduces pain but is non-euphoric

Developer says the new drug reduces pain without creating the euphoria that led to the opioid epidemic

Drug developer Nektar Therapeutics has announced positive results from a phase III trial of its experimental opioid painkiller called NKTR-181. The drug “significantly reduced pain in patients with moderate to severe chronic low back pain, had a favorable safety profile and was well tolerated.”

The San Francisco-based biotech company expects that NKTR-181 will be a huge boon for safer pain treatment, as well as a financial blockbuster, because it’s the first “mu-opioid agonist” to treat pain without causing the opioid euphoria of other opioid painkillers that launched the opioid epidemic.

The term “mu-opioid agonist” refers to the opioid receptors in the central nervous system that respond to the presence of opioids such as morphine, heroin, methadone, oxycodone, hydromorphone, etc.

Phase III trial a success

In the drug’s phase III trial, 610 patients suffering from chronic low back pain were given up to 400 mg of NKTR-181 twice daily and pain scores dropped an average of 63 percent. The trial then transitioned into a 12-week, double-blind phase during which half of the patients received the NKTR-181 and the other a placebo. Average pain scores increased in both groups, but significantly higher in the placebo arm – 1.46 compared to 0.92 for the NKTR-181 arm.

This difference is “statistically significant, though a long way from living pain free,” the company said. Pain relief, side effects and sleep factors appeared to be in line with existing opioid painkillers, however.

A new pharmaceutical generally goes through a series of four trial phases:

  • Phase I on a small group of people for the first time to evaluate safety, determine safe dosage levels and identify side effects
  • Phase II on a larger group of people to further evaluate safety and effectiveness
  • Phase III on large groups to confirm effectiveness, monitor side effects, compare it to commonly used treatments, and collect all the data needed to use it safely and effectively in the real world.
  • Phase IV involves continuing studies after the drug has reached the market to collect ongoing info on the drug’s effect in various populations as well as side effects associated with long-term use.

Testing “human abuse potential”

In March 2017, a separate “human abuse potential” trial of NKTR-181 found almost no difference between the painkiller and a placebo. The results, published in the journal of the American Academy of Pain Medicine, detailed how varying doses of NKTR-181 were tested for abuse potential – scores rated for “drug liking” and “feeling high” – and even the full Phase III dose of 400 mg scored significantly lower than 40 mg oxycodone. In addition, all doses of NKTR-181 scored lower on sleepiness than 40 mg of oxycodone.

Drug-liking and feeling high are two of the most important metrics to assess the abuse potential of a medicine.

“It is clear that there is a pressing societal need for better and safer analgesics,” said Dr. Jack Henningfield, Ph.D., Adjunct Professor of Behavioral Biology in the Department of Psychiatry and Behavioral Sciences at the Johns Hopkins University School of Medicine. “In the human abuse potential study, even the highest analgesic dose of NKTR-181 was barely distinguishable from placebo with respect to both drug-liking and feeling high and these effects were modest compared to those produced by oxycodone.”

Importantly, as NKTR-181 is a new chemical entity, the properties of NKTR-181 are inherent to its molecular structure and independent of any abuse-deterrent formulation, Henningfield added. “Today’s reported efficacy and safety results, along with the human abuse potential data published this past week in Pain Medicine, suggest NKTR-181 may be a major advance towards safer opioid therapy for the treatment of moderate to severe chronic pain,” he said.

“Important advancement in pain medication”

Nektar CEO Howard Robin trumpeted the potential for such a new painkiller. “As a new molecule, NKTR-181 has a highly differentiated profile with the potential to be one of the most important advancements in pain medication,” he said, adding that the company is committed to bringing the drug to patients “as quickly as possible.”

Nektar says it has no plans to market the drug itself. As with other drugs it’s developed, the company is looking for partners – in this case a pharmaceutical player “that has a strong presence and long-term commitment in the pain market” – to out-license manufacturing and marketing.

Nektar already partners with numerous other drug companies to whom it grants licenses to develop and in some cases manufacture and market its new drugs, for which Nektar receives royalties and/or manufacturing revenues. For example, Astra-Zeneca and Daichi-Sanyo are partners for Nektar’s recently developed drug Movantik, which treats opioid-induced constipation – a frequent and significant side effect among chronic pain patients on opioid therapies.

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