Simulated time behaviour of parent drug and its metabolites. The curves have ben obtained by simulating a mass action model of the interactions depicted in the cartoon of Figure 2. A level of noise equal to the 7% of the concentration values has been artificially introduced to simulate the presence of experimental uncertainties. In this model we asssumed that both the intra- and the intra-cellular concetration of dFdU reach the equilibrium within the first four hours. (A) Time behaviour of extra- and intra-cellular concentrations of dFdC. (B) Time behaviour of the concentrations of phisphorylated metabolites of dFdC. (C) Time behaviour of the concentrations of phisphorylated metabolites of dFdU.