Figure 1. Example BRAID response surfaces.

Unless otherwise specified, in all surfaces, ID_M,A = 1.5 μM, ID_M,B = 1.5 μM, n_a = n_b = 3, E₀ = 0, E_f,A = E_f,B = 100, and κ = 0. Isoboles in all plots represent a change in effect equal to 10. (a) A basic additive response surface. (b) Lower Hill slopes (n_a = n_b = 1). (c) Differing Hill slopes (n_a = 1, n_b = 3). (d) Mild synergy (κ = 0.75). (e) Strong synergy (κ = 2.5). (f) Differing final effects (E_f,A = 100, E_f,B = 55). (g) Mild antagonism (κ = −0.3). (h) Severe antagonism (κ = −1.2). (i) A more complex surface, with n_a = 2.7, n_b = 3.2, E_f,A = 100, E_f,B = 75, and κ = −0.5. Note that the isoboles, particularly at higher effect levels, show regions of convexity and concavity; traditionally, surfaces like this would necessitate varying domains of synergy and antagonism. However, by allowing the maximal effects of the two drugs to differ, such surfaces can be modeled with a single interaction parameter.