Operating Characteristics of Restrictions on Skipping Dose Level for Adaptive Dose-Finding Method in Two-Agent Phase I Trials

The model-based dose-finding method for the combination of two agents consists of the following three components; 1) dose-toxicity model, 2) start-up dose allocation rule before model-based dose-finding stage, and 3) restriction on skipping dose levels in the dose-finding algorithm. Although many authors have developed flexible dose-toxicity models as well as the start-up dose allocation rule, the restriction on skipping dose levels during the trial, has not been adequately studied. In this paper, we propose a new restriction that permits the dropping of dose combinations with toxicity probabilities that are expected to be statistically high, during the trial. We also compared the operating characteristics of the proposed strategy with those of conventional restrictions using simulation studies. Based on the results of the simulation studies, we were able to determine the performance of these strategies and provide some recommendations for their uses.