A phase 3, multicenter study to assess the 1-year safety and tolerability of a combination of olanzapine and samidorphan in patients with schizophrenia: Results from the ENLIGHTEN-2 long-term extension.

Aim: A combination of olanzapine and samidorphan (OLZ/SAM) is in development for the treatment of patients with schizophrenia or bipolar I disorder and is intended to provide the efficacy of olanzapine while mitigating olanzapine-associated weight gain. This 52-week open-label extension (NCT02873208; ENLIGHTEN-2-EXT) assessed the long-term safety and tolerability of OLZ/SAM in patients with schizophrenia.

Methods: Patients completing the 24-week randomized, double-blind, phase 3 ENLIGHTEN-2 study (NCT02694328) comparing weight change from baseline to week 24 with OLZ/SAM versus olanzapine were eligible to enroll in the 52-week ENLIGHTEN-2-EXT study. Assessments included adverse events (AEs; each visit), weight/waist circumference (every other week for the first 8 weeks, then every 4 weeks thereafter), metabolic laboratory parameters (weeks 4, 12, 24, 36, and 52), Positive and Negative Syndrome Scale (PANSS) scores (weeks 2, 4, 8, 12, 24, 36, and 52), and Clinical Global Impression-Severity (CGI-S) scores (weeks 2 and 4, then every 4 weeks thereafter through week 48, and at week 52). Analyses were based on observed results using descriptive statistics. Baseline was relative to the first OLZ/SAM dose in the extension study.

Results: In total, 265 patients were enrolled and received at least 1 dose of OLZ/SAM; 167 (63.0%) completed the 52-week 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, the mean (SD) change from baseline for weight and waist circumference was -0.03 (6.17) kg and - 0.35 (6.12) cm, respectively. Changes in fasting lipid and glycemic parameters were generally small and remained stable over 52 weeks. During the extension, PANSS total scores remained stable, and at week 52, 81.3% of patients had CGI-S scores of 3 or less, reflecting mild illness severity.

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