To cite PoPdesign in publications use:

  Fu C, Zhou S (2020). “Posterior predictive design for phase I
  clinical trials.” _Manuscript in preparation_.

A BibTeX entry for LaTeX users is

  @Article{,
    title = {Posterior predictive design for phase I clinical trials.},
    author = {Chenqi Fu and Shouhao Zhou},
    journal = {Manuscript in preparation},
    year = {2020},
  }