Sample Size Considerations for a Phase III Clinical Trial with Diluted Treatment Effect

In clinical development of new drugs, investment increases over time—Phase III investment can be up to hundreds of millions of dollars. However, some drugs failed because the treatment effect in Phase III is diluted from Phase II. When this is the case, a few strategies can be contemplated by the project team develops this new drug. One is to increase sample size based on the uniform and truncated normal prior distribution. Another is to design the Phase III trials using the average success probability (ASP) approach. Finally, the numerical simulations are carried out to calculate the sample size for the Phase III clinical trial with diluted treatment effect.