Efficacy
The efficacy of OSC in the treatment of schizophrenia in adults is supported, in part, by the extensive legacy of studies of orally administered olanzapine.2 For OSC specifically, acute efficacy was primarily demonstrated in a randomized, double-blind, phase 3, 4-week study establishing superiority vs placebo in acutely exacerbated patients with schizophrenia.8 Mitigation of weight gain was assessed separately in a randomized, double-blind, phase 3, 24-week study comparing OSC with olanzapine in non-acute outpatients with schizophrenia.10 Both of these 2 trials were accompanied by 52-week open-label extension studies.9,11
The 4-week study evaluated the antipsychotic efficacy of OSC in 401 patients experiencing an acute exacerbation or relapse of schizophrenia who required inpatient treatment.8 Patients were required to have a Positive and Negative Syndrome Scale (PANSS) total score ≥80, with a score ≥4 on at least 3 of selected positive symptoms, and a Clinical Global Impression-Severity (CGI-S) score ≥4 at baseline and screening. Patients were required to be inpatients for the first 2 weeks of the study, and were encouraged to remain as inpatients for all 4 weeks. Patients were randomized to receive OSC, olanzapine, or placebo. Dosing was once-daily and flexible based on clinical response and tolerability for the first 2 weeks of the study, and fixed thereafter. Patients assigned to OSC could receive 10 mg/10 mg or 20 mg/10 mg, and patients randomized to olanzapine could receive 10 mg or 20 mg. The study compared OSC with placebo, with olanzapine serving as an active control. Treatment with OSC resulted in significant improvements in symptoms compared with placebo at Week 4, as measured by changes in PANSS total scores from baseline. Improvement in PANSS scores with OSC relative to placebo was similar to that observed with olanzapine. The antipsychotic efficacy of OSC relative to placebo was also supported by improvements in CGI-S scores. Thus, the inclusion of samidorphan in OSC did not negatively impact the antipsychotic efficacy of olanzapine.
In the 24-week study, 561 patients were randomized to OSC or olanzapine.10 There was no placebo control. Patients were treated with doses of OSC 10 mg/10 mg or 20 mg/10 mg, or with doses of olanzapine 10 mg or 20 mg. Dosing was flexible for the first 4 weeks of the study and fixed thereafter. Eligible patients were age 18 to 55 years (younger than the 4-week study, where the maximum age was 70 years), with a body mass index of 18 to 30 kg/m2 (lower than the upper limit of 40 kg/m2 used in the 4-week study). In contrast to the acutely exacerbated patients in the 4-week study, patients were required to have a PANSS total score of 50 to 90, CGI-S score ≤4, and symptoms suitable for outpatient treatment. The co-primary endpoints were percent change from baseline in body weight and proportion of patients who gained ≥10% body weight at Week 24. Treatment with OSC or olanzapine resulted in similar improvements in PANSS total and CGI-S scores, but treatment with OSC was associated with statistically significantly less weight gain than treatment with olanzapine, and with a smaller proportion of patients who gained ≥10% body weight. The least squares mean percent weight change from baseline to the end of treatment was 4.2% with OSC vs 6.6% with olanzapine. Although patients treated with OSC or olanzapine had similar weight gain for the first 4 weeks of treatment, OSC weight gain stabilized after approximately the 6th week, whereas patients who received olanzapine continued to gain weight throughout the remainder of the treatment period. The risk of gaining ≥10% body weight from baseline was reduced by 50% with OSC compared with olanzapine. Moreover, the odds of gaining ≥7% body weight from baseline at Week 24 were also reduced by 50% for OSC compared with olanzapine. OSC was also associated with smaller increases in waist circumference compared with olanzapine, which was observable as early as Week 1. The risk of experiencing a 5-cm increase in waist circumference was 50% lower for patients treated with OSC vs olanzapine, a relevant threshold in assessing risk of all-cause mortality and cardiovascular disease.20 However, changes in metabolic laboratory parameters in patients treated with OSC or olanzapine were generally small and were similar between groups. In addition, there were little differences between the 2 treatment groups in metabolic parameter changes considered to be of potential clinical significance, based on commonly used thresholds.
Patients on stable, chronic olanzapine therapy were not specifically studied, so the weight effect of switching from olanzapine to OSC is unknown.For bipolar I manic or mixed episodes, the use of OSC as monotherapy or in combination with lithium or valproate, as well as for maintenance monotherapy, was approved based on legacy clinical trials with olanzapine, as described in product labeling,2,4 as well as pharmacokinetic data evidencing that OSC did not have a clinically significant effect on the pharmacokinetics of lithium or valproate.13 A study is in progress to evaluate the effect of OSC compared with olanzapine on body weight in young adults with schizophrenia, schizophreniform, or bipolar I disorder who are early in their illness (ClinicalTrials.gov identifier: NCT03187769).
Overall tolerability and safety
The systemic safety and tolerability profile for OSC would be expected to be similar to that for olanzapine, unless there are adverse events that are specifically related to the samidorphan component. In the 4-week acute study described above,8 adverse events that occurred at least twice the rate of placebo with OSC included increased weight (18.7%, 14.3%, 3.0%, for OSC, olanzapine, and placebo, respectively), somnolence (9.0%, 9.8%, 2.2%), dry mouth (7.5%, 5.3%, 0.7%), and headache (6.0%, 5.3%, 3.0%). In the 24-week study,10 which did not have a placebo control, the most commonly reported adverse events (≥10% of patients) were increased weight (24.8% vs 36.2% for OSC vs olanzapine), somnolence (21.2% vs 18.1%), dry mouth (12.8% vs 8.0%), and increased appetite (10.9% vs 12.3%). In both studies, rates of discontinuation due to adverse events were low and similar between groups (in the 4-week study, 1.5% for OSC, 2.3% for olanzapine, and 5.2% for placebo; in the 24-week study, 12.0% for OSC and 9.8% for olanzapine).
In the 2 open-label, phase 3, 52-week extension studies,9,11 long-term tolerability was evidenced by low rates discontinuation due to adverse events (≤6%). Neither extension study reported any clinically meaningful changes over time in hematology, biochemistry, vital signs, or electrocardiogram parameters.3 In addition to durability of antipsychotic response as evidenced by sustained improvements in PANSS and CGI-S scores over time, waist circumference and weight remained stable, and the observed long-term changes in weight were consistent with weight changes observed with other second-generation antipsychotics.3 Long-term changes in metabolic laboratory parameter values were small and remained stable, and there was little change in glycosylated hemoglobin (hemoglobin A1c) values, which suggests that glycemic control was maintained with long-term OSC treatment.3 Caveats to consider are that the extension studies were open label without comparators, and they may have selected for patients who responded favorably to OSC treatment in the preceding studies.3Warnings and precautions in OSC product labeling are generally similar to those for other second-generation antipsychotics,21 other than warnings and precautions specifically related to samidorphan being an opioid antagonist, and special mention of “Drug Reaction with Eosinophilia and Systemic Symptoms” and “Anticholinergic (Antimuscarinic) Effects” warnings, which also are contained in the olanzapine legacy label.2,4
Summary
Olanzapine has a plethora of evidence supporting its robust efficacy profile5,6; however, its use is stymied by an unfavorable weight and metabolic profile.7 OSC may help mitigate at least some of the weight gain that would be expected with the use of olanzapine alone in the long-term treatment of patients with schizophrenia or bipolar I disorder. The addition of samidorphan does not deleteriously affect the efficacy of olanzapine, but decreases the risk of gaining ≥10% or ≥7% of baseline body weight by approximately 50% compared with olanzapine alone. Increase in waist circumference, a proxy for how much metabolically active fat one has, is lower with OSC than it is with olanzapine. Because samidorphan is an opioid receptor antagonist, OSC is contraindicated in patients using opioids and in those undergoing acute opioid withdrawal. Dosage strengths available for OSC parallel those for olanzapine, and all strengths including the same fixed dose of samidorphan—10 mg—so advise patients not to double up on the tablets, and to not split them.
Related Resource
• Olanzapine and samidorphan (Lybalvi) prescribing information. https://www.lybalvi.com/lybalvi-prescribing-information.pdf
Drug Brand Names
Diazepam • Valium
Lithium • Eskalith, Lithobid
Olanzapine • Zyprexa
Olanzapine-fluoxetine combination • Symbyax
Olanzapine-samidorphan combination • Lybalvi
Valproate • Depakote, Depakene
Bottom Line
Olanzapine-samidorphan combination (OSC) is intended to mitigate some of the weight gain anticipated when using olanzapine alone. For clinicians who have prescribed olanzapine and have seen its therapeutic benefits, OSC will be a welcome addition to the therapeutic armamentarium. For practitioners who may have avoided olanzapine entirely, OSC can provide another means of offering this therapeutic option and counter “olanzapine hesitancy.”