To cite rentrez in publications use:

  Winter, D. J. (2017) rentrez: an R package for the NCBI eUtils API
  The R Journal 9(2):520-526

A BibTeX entry for LaTeX users is

  @Article{,
    title = {{rentrez}: an R package for the NCBI eUtils API},
    author = {David J. Winter},
    journal = {The R Journal},
    year = {2017},
    volume = {9},
    issue = {2},
    pages = {520--526},
  }