To cite package PK in publications use:

Jaki T and Wolfsegger MJ (2011) Estimation of pharmacokinetic parameters with the R package PK. Pharmaceutical Statistics. Vol 10(No 3), 294-288. doi:10.1002/pst.449

Corresponding BibTeX entry:

  @Article{,
    title = {Estimation of pharmacokinetic parameters with the R
      package PK},
    author = {Thomas Jaki and Martin Wolfsegger},
    year = {2011},
    journal = {Pharmaceutical statistics},
    volume = {10},
    number = {3},
    pages = {284-288},
    note = {DOI: 10.1002/pst.449},
    url = {http://CRAN.R-project.org/package=PK},
  }