Phase 3 Safety and Tolerability Results of the Combination Olanzapine and Samidorphan in Patients With Schizophrenia: The 1 Year ENLIGHTEN-2-Extension

Background: Combination olanzapine and samidorphan (OLZ/SAM) is in development for treatment of schizophrenia and bipolar I disorder and is intended to provide the antipsychotic efficacy of olanzapine while mitigating olanzapine-associated weight gain. This 52-week open-label extension study (NCT02873208; ENLIGHTEN-2-EXT) in schizophrenia assessed the safety and tolerability of OLZ/SAM.

Methods: Patients completing the 24-week, randomized, double-blind, phase 3 ENLIGHTEN-2 study comparing weight gain with OLZ/SAM vs olanzapine were eligible for ENLIGHTEN-2-EXT enrollment. Initial OLZ/SAM doses were based on olanzapine dose (10 or 20 mg) received at the conclusion of ENLIGHTEN-2; subsequent olanzapine dose adjustments were allowed. The samidorphan dose (10 mg) remained fixed throughout. Assessments included adverse events (AEs), weight, waist circumference, metabolic laboratory parameters, and Positive and Negative Syndrome Scale (PANSS) scores. Analyses were based on observed results using descriptive statistics. Baseline was relative to the first OLZ/SAM dose in the extension study.

Results: 265 patients received OLZ/SAM; 167 (63.0%) completed the extension study. Common AEs (≥5%) were weight decreased (n=23; 8.7%), extra dose administered (n=21; 7.9%), headache (n=18; 6.8%), and weight increased (n=16; 6.0%). At week 52, mean (SD) change from baseline for weight and waist circumference was _0.03 (6.216) kg and _0.35 (6.115) cm, respectively. Changes in fasting lipid and glycemic parameters were generally small and remained stable over 52 weeks. PANSS total scores remained stable during the extension.

Conclusions: OLZ/SAM was generally well tolerated over 52 weeks. Weight, waist circumference, metabolic laboratory parameters, and schizophrenia symptoms remained stable throughout the study.