Two of the highlighted agents – pimavanserin and SEP-363856 – were designed to eschew the traditional antipsychotic target, the dopamine D2 receptor, in favor of other mechanisms of action aimed at the negative symptoms of schizophrenia, for which there is a long-recognized major unmet need for better therapies.
A third agent, known for now as ALKS 3831, is composed of a combination of olanzapine and samidorphan, an opioid receptor antagonist. This once-daily oral combination of olanzapine/samidorphan (OLA/SAM) is designed to retain the clinical efficacy of olanzapine while mitigating the drug’s limiting side effect of substantial weight gain.
OLA/SAM New Drug Application expected soon
Christine Graham, PhD, presented highlights of the pivotal phase 3, a double-blind clinical trial in which 661 U.S. outpatients with schizophrenia were randomized to OLA/SAM or olanzapine alone at 10 or 20 mg/day for 24 weeks, at which point everyone was switched to open-label OLA/SAM at 10 or 20 mg/10 mg for an additional 52-week extension safety study.
At 24 weeks, the OLA/SAM group had a mean 4.21% weight gain from baseline, significantly less than the 6.59% gain with olanzapine alone. A clinically meaningful and unwelcome weight gain of 7% or greater occurred in 27.5% of OLA/SAM patients, compared with 42.7% of controls, for an adjusted 50% reduction in risk in the group on the investigational medication. Similarly, a 10% or greater weight gain occurred in 17.8% of OLA/SAM patients and 29.8% of controls; once again, that represented a 50% relative risk reduction. The two therapies were equally effective, achieving roughly 10-point reductions in the Positive and Negative Syndrome Scale () for schizophrenia total score.
Both treatments showed similar weight gain trajectories for the first 4 weeks. However, by week 6 the trajectories diverged, with body weight plateauing in the OLA/SAM group and remaining stable throughout the remainder of the 76-week, two-part study. Meanwhile, body weight continued to climb in the olanzapine-only group throughout the 24 weeks, reported Dr. Graham, senior clinical research scientist at Alkermes, in Waltham, Mass.
“The waist circumference results were surprising: We saw that waist circumference separated between the two groups as early as week 1, considerably earlier than the week 6 separation in weight. This suggests to us that even when weight gain is similar between the two treatments, OLA/SAM is showing an early effect at limiting central fat accumulation – and this has important health implications, as central fat has been shown to be potentially pathogenic for developing diabetes, cardiovascular disease, and even some forms of cancer,” she said.
The safety profile of OLA/SAM was essentially the same as for olanzapine-only, with the exception of the weight gain.
Alkermes is planning to submit its New Drug Application for OLA/SAM to the Food and Drug Administration before the year’s end. FDA officials have urged the company to broaden the application to include not only the treatment of schizophrenia, but bipolar I disorder as well, since olanzapine is an approved, well-established treatment for that disorder. Dr. Graham and coinvestigators have demonstrated that OLA/SAM has no clinically significant effect on the pharmacokinetics of lithium or valproate (Clin Drug Investig. 2019 Oct 4..