Investigating the efficacy and safety of olanzapine prophylaxis for opioid-induced nausea and vomiting (JORTC-PAL20): a study protocol for an open-label, single-arm exploratory study.

Introduction: In opioid therapy for cancer pain, opioid-induced nausea and vomiting (OINV) occur in 20%-40% of patients during initial opioid treatment or increasing opioid doses. OINV result in failure to achieve pain relief due to poor opioid adherence. Therefore, antiemetics are used to prevent OINV, but their efficacy and safety in this context have not yet been fully elucidated. Olanzapine is a promising antiemetic for the prophylaxis of chemotherapy-induced nausea and vomiting.

Methods And Analysis: This single-arm, single-centre exploratory study will evaluate the prophylactic antiemetic efficacy and safety of 5 mg olanzapine in patients with cancer pain who are withholding initial regular opioid therapy. Thirty-five patients will be enrolled. The primary endpoint is the proportion of patients achieving complete control (CC) of OINV during 5 days of opioid treatment. CC was defined as the absence of emetic episodes, no need for rescue medication to treat nausea, and minimal or no nausea (3 or less on an 11-point categorical scale). Secondary endpoints include the complete response, defined as no emetic episodes and no use of rescue medication during the overall assessment period, the time from opioid initiation to first emetic episode, the time from opioid initiation to first rescue antiemetic administration, and adverse events graded by Patient-Reported Outcome (PRO) Common Terminology Criteria for Adverse Events (CTCAE) version 1.0 and CTCAE version 5.0.

Ethics And Dissemination: This study protocol was approved by National Cancer Center Hospital Certified Review Board. The results will be used as preliminary data to conduct a validation study.

Trial Registration Number: Japan Registry of Clinical Trials (jRCT) jRCTs031220008.