TABLE 4

Description and symbols of synergism or antagonism in drug combination studies analyzed with the combination index method The combination index method is based on those described by Chou and Talahay (1984) and the computer software of Chou and Martin (2005). The ranges of CI and the symbols are refined from those described earlier by Chou (1991). CI < 1, = 1, and > 1 indicate synergism, additive effect, and antagonism, respectively [modified from Chou and Martin (2005)].

Range of Combination Index Description Graded Symbols Graphic Symbols
<0.1 Very strong synergism +++++ Embedded Image
0.1–0.3 Strong synergism ++++
0.3–0.7 Synergism +++
0.7–0.85 Moderate synergism ++
0.85–0.90 Slight synergism +
0.90–1.10 Nearly additive ±
1.10–1.20 Slight antagonism
1.20–1.45 Moderate antagonism – –
1.45–3.3 Antagonism – – –
3.3–10 Strong antagonism – – – –
>10 Very strong antagonism – – – – –