A clinical trial loses access to some of its experimental treatment conditions: What can be done?

This commentary examines methodological and ethical problems encountered when a multi-arm clinical trial loses access to one or more of its arms, using the Retention Phase of the NIDA Clinical Trials Network CTN-0100 study, Optimizing Retention, Duration and Discontinuation Strategies for Opioid Use Disorder Pharmacotherapy (RDD) as an example. RDD is a community-based, multi-site trial testing strategies to reduce dropout from medication treatment for opioid use disorder. Among patients with opioid use disorder initiating buprenorphine treatment, the original design was a 3 by 2 factorial comprising 3 pharmacological conditions (Standard-Dose sublingual buprenorphine-16 mg/day target [SL-BUP 16], High-Dose sublingual buprenorphine-32 mg/day target [SL-BUP 32], or extended-release injectable buprenorphine [XR-BUP]), crossed with 2 behavioral conditions: medical management with vs. without a technology-based digital therapeutic app providing cognitive behavioral therapy lessons and contingency management. The trial experienced two major disruptions to study interventions: 1) The supply of XR-BUP became temporarily unavailable due to manufacturing problems; and 2) The company supplying the digital therapeutic app went bankrupt, rendering the original app permanently unavailable. Questions considered by the study lead team included: 1) Whether to pause recruitment into the trial altogether or continue recruitment into truncated designs omitting the unavailable interventions; 2) How to account for participants who did not experience full exposure to the halted interventions; 3) Whether to substitute a similar intervention; and 4) The problem of concurrent randomizations, namely that a truncated design does not contain all the concurrent randomizations of the full design, introducing risk of confounding or bias. This experience from the RDD trial demonstrates how multi-arm clinical trials that lose access to an intervention arm can continue with a truncated design, allowing continued progress on study aims, while balancing methodological purity with the pragmatic imperative to keep the trial running and respect subjects' participation.