kinfit and mkin provide calculation routines based on the FOCUS Kinetics Report (2006). In kinfit, only kinetic models for simple degradation datasets are included. In mkin, there is no theoretical limit for the number of compartments or metabolites to model.
Please note that no warranty is implied for correctness of results or fitness for a particular purpose.
An overview of the current capabilities of the kinfit package (rapid and simultaneous fitting of the kinetic models recommended by the FOCUS group for parent only) is given in the kinfit documentation page which also contains the package vignette.
You can install the development version of the packages by using the R commands
install.packages("kinfit", repos= c("http://R-Forge.R-project.org", getOption("repos")))
install.packages("mkin", repos= c("http://R-Forge.R-project.org", getOption("repos")))
or you can get the stable release versions from CRAN using