Feasibility of a randomised controlled trial comparing opioid dose escalation with low-dose methadone addition for refractory cancer pain: JORTC-PAL23/NCCH2309 - protocol.

INTRODUCTION

Methadone exerts analgesic effects through μ-opioid receptor affinity and N-methyl-D-aspartate receptor antagonism, which may benefit refractory cancer pain with neuropathic components. Methadone can be introduced by the 'stop-and-go' (SAG) method or the 'add-on' (AO) method, in which low-dose methadone is added to existing opioids. Observational studies suggest AO may improve pain control but no double-blind randomised controlled trial (RCT) has evaluated this approach. Therefore, the primary aim of this study is to assess the feasibility of conducting a double-blind RCT comparing methadone AO therapy with opioid dose escalation according to standard practice for refractory cancer pain while also exploring safety and preliminary efficacy signals.

METHODS AND ANALYSIS: A two-centre, randomised, double-blind, two-arm feasibility trial will enrol 22 patients with advanced or recurrent cancer and inadequately controlled pain (oral morphine equivalent daily dose 60-300 mg). Participants will be allocated 1:1 to the methadone AO or opioid-escalation group using a web-based randomisation system with the minimisation method. The primary endpoint is the completion rate of the 2-week study treatment. Secondary outcomes include pain intensity (Brief Pain Inventory), time to adequate pain control, achievement of a personalised pain goal, adverse events (Common Terminology Criteria for Adverse Events (CTCAE)/Patient-Reported Outcomes version of the CTCAE) and quality of life (European Organisation for Research and Treatment of Cancer-Quality of Life Questionnaire Core 15-PAL). Feasibility will be determined based on achieving a treatment completion rate of 70% or higher.

ETHICS AND DISSEMINATION: The protocol was approved by the Certified Review Board of the National Cancer Centre Hospital (CRB3180008). Written informed consent will be obtained from all participants. The trial is registered in the Japan Registry of Clinical Trials. Results will be published in peer-reviewed journals and presented at international conferences.

TRIAL REGISTRATION NUMBER: jRCTs031240220.