A randomized, double-blind, placebo-controlled proof of concept study to evaluate samidorphan in the prevention of olanzapine-induced weight gain in healthy volunteers

Antipsychotic medications are associated with weight gain and adverse metabolic effects that complicate the treatment and management of schizophrenia. Olanzapine (OLZ) in particular is associated with significant weight gain and adverse metabolic effects. The present Phase 1, proof of concept, multicenter, randomized, double-blind, placebo-controlled study investigated the safety and effect on weight of a combination of OLZ (10mg) and the opioid modulator samidorphan (SAM; 5mg) in comparison to OLZ alone in healthy, male normal weight volunteers. Altogether, 106 male subjects with stable body weight and BMI 18-25kg/m2 were randomized to OLZ alone, OLZ+SAM, SAM alone, or placebo in a 2:2:1:1 ratio. The primary efficacy endpoint, mean (SD) body weight change from baseline to last assessment in the 3-week treatment period, was significantly less for OLZ+SAM vs. OLZ alone subjects [+2.2 (1.4) kg vs. +3.1 (1.9) kg; respectively; p=0.02]. In contrast, there was no significant difference in weight from baseline for either SAM or placebo [+0.1 (1.0) kg and +0.8 (1.4) kg, respectively]; p=0.09. Overall, OLZ+SAM compared to OLZ alone had similar safety and tolerability. In addition, less nausea was observed in subjects given OLZ+SAM compared to SAM alone. Thus, OLZ+SAM may offer effective treatment of schizophrenia with less weight gain and metabolic risk. Additional research exploring additional doses over longer durations in psychiatric populations is warranted.