could not be used because there were samples without API, which precluded the calculation on these parameters. Table shows the model parameters for each response. Except for STDCapryol, all surfaces were described by cubic models, i.e., there were complex interactions between the compounds. All the coefficients representing the pure compounds were significant for all the responses studied. The interactions of the excipients were important for DHICapryol, the interactions of CP with BTB were important for the DHICP and STDCP models, while the interactions between butamben and CAP were important for DHICapryol. This indicates that not only the presence of API, but the interaction with the excipients affects the homogeneity/spatial distribution of the compounds in a sample.