The method of Greco et al. (1990) has many advantages over other methods of analyzing drug-drug interactions. It can accept input data over any concentration range, rather than just fixed-ratio combinations. It calculates an interaction parameter that describes a best fit to the entire response surface, and also calculates statistical confidence limits for the parameter estimates. The parameters calculated by GRECFIT for in vitro combinations can be used by DPDMODEL to predict in vivo interactions.
Despite its many advantages, Greco’s method has been less widely used than other less rigorous methods because of its computational complexity. GRECFIT provides a user-friendly program that simplifies the use of this powerful technique.
Graphical output is provided in a variety of formats: 3-dimensional response surfaces, isobolograms, and plots of combination index (CI) as a function of fractional activity (as used by CALCUSYNTM).