Low-dose versus standard-dose olanzapine with triple antiemetic therapy for prevention of highly emetogenic chemotherapy-induced nausea and vomiting in patients with solid tumours: a single-centre, open-label, non-inferiority, randomised, controlled, phase 3 trial

Background Olanzapine is an effective antiemetic agent but it results in substantial daytime somnolence when administered at the standard dose. Our aim was to compare the efficacy of low-dose versus standard-dose olanzapine after highly emetogenic chemotherapy in patients with solid tumours. Methods This was a single-centre, open-label, non-inferiority, randomised, controlled, phase 3 trial done in a tertiary care referral centre in India (Tata Memorial Centre, Homi Bhabha National Institute, Mumbai). Patients aged 13-75 years with an Eastern Cooperative Oncology Group performance status of 0-2, who were receiving doxorubicin-cyclophosphamide or high-dose cisplatin for a solid tumour were eligible. Patients were randomly assigned (1:1), with block randomisation (block sizes of 2 or 4) and stratified by sex, age (>= 55 or <55 years), and chemotherapy regimen, to receive low-dose (25 mg) oral olanzapine or standard-dose (100 mg) oral olanzapine daily for 4 days, in combination with a triple antiemetic regimen. Study staff were masked to treatment allocation but patients were aware of their group assignment. The primary endpoint was complete control, defined as no emetic episodes, no rescue medications, and no or mild nausea in the overall phase (0-120 hours), assessed in the modified intention-to-treat (mITT) population (ie, all eligible patients who received protocol-specified treatment, excluding those who had eligibility violations and who withdrew consent after randomisation). Daytime somnolence was the safety endpoint of interest. Non-inferiority was shown if the upper limit of the one-sided 95% CI for the difference in the complete control proportions between the treatment groups excluded the non-inferiority margin of 10%. This study is registered with the Clinical Trial Registry India, CTRI/2021/01/030233, is closed to accrual, and this is the final data analysis. Results Between Feb 9, 2021, and May 30, 2023, 356 patients were pre-screened for eligibility, of whom 275 patients were enrolled and randomly assigned (134 to the 25 mg olanzapine group and 141 to the 100 mg olanzapine group). 267 patients (132 in the 25 mg group and 135 in the 100 mg group) were included in the mITT population, of whom 252 (94%) were female, 15 (6%) were male, and 242 (91%) had breast cancer. 59 (45%) of 132 patients in the 25 mg olanzapine group had complete control in the overall phase versus 59 (44%) of 135 in the 100 mg olanzapine group (difference -10% [one-sided 95% CI -1000 to 90]; p=087). In the overall phase, there were significantly fewer patients in the 25 mg olanzapine group than in the 100 mg olanzapine group with daytime somnolence of any grade (86 [65%] of 132 vs 121 [90%] of 135; p<00001) and of severe grade on day 1 (six]5%] vs 54 [40%]; p<00001). Interpretation Our findings suggest that olanzapine 25 mg is non-inferior to 100 mg in antiemetic efficacy and results in reduced occurrence of daytime somnolence among patients receiving highly emetic chemotherapy and should be considered as a new standard of care.