The 24-week study met its primary and key secondary endpoints for both dosage regimens, according to the company.
“The clinical data from our Phase III study also showed that outcomes with RBP-6000 are consistent across other secondary clinical endpoints, including control of craving and withdrawal symptoms, as compared to placebo,” chief scientific officer Christian Heidbreder said in prepared remarks. “These outcomes started with the first dose of RBP-6000, which achieved buprenorphine plasma concentrations ≥ 2 ng/mL and predicted whole brain mu-opioid receptor occupancy of ≥ 70%, and were also maintained for the one-month dosing intervals and for the entire treatment duration.”
The trial enrolled 504 treatment-seeking adults, ages 19 to 64, with moderate or severe opioid use disorder who were not receiving medication-assisted treatment. The patients were randomized to receive either 1 of 2 dosage regimens of RBP-6000 or palcebo.
Prior to randomization, all study participants were inducted and stabilized with a sublingual film of Suboxone (buprenorphine and naloxone) to ensure that they weren’t allergic to buprenorphine and to suppress opioid withdrawal signs, Indivior said.
The participants were randomized to receive 6 once-monthly 300 milligram doses, 2 once-monthly 300 milligram doses followed by 4 once-monthly 100 milligram doses or 6 once-monthly subcutaneous placebo injections. The study subjects also received manual-guided psychosocial support at least once a week.
The primary efficacy endpoint was the mean percentage abstinence, or weeks spent opioid-free, combined with self-reports negative for illicit opioid use from week 5 to week 24. The key secondary endpoint was treatment success, defined as any participant with greater than or equal to 80% of urine samples negative for opioids.
RBP-6000 met the primary efficacy endpoint and both dosage regimens yielded significantly higher abstinence rates compared to the placebo. Both dosages also met the key secondary endpoint of treatment success, Indivior reported.
The depot was generally well tolerated in the late-stage trial, as 2.7% of subjects on both dosage regimens combined experienced a serious treatment-emergent adverse event compared to 5% of participants on placebo.
Also, approximately 60% of patients in each dosage group finished the study versus 33.3% of the people taking a placebo.
“Opioid use disorder is a chronic, relapsing medical condition with multiple factors playing a role and impacting patient outcomes, including control of withdrawal symptoms, cravings and relapse to illicit opioid use,” principal investigator Dr. Amit Vijapura said. “If approved, RBP-6000 could help address the unmet needs of patients and represent a potentially important new option for the treatment of opioid use disorder.”
Indivior submitted a new drug application to the FDA last month, looking for marketing approval for RBP-6000 as a treatment for adults with moderate-to-severe opioid use disorder in combination with counseling and psychosocial support.