Table 1. Combination Index (CI) values and Dose Reduction Index (DRI) for combined treatments of vitamin D and IR (A) or Zemplar and IR (B).
| Mutually nonexclusive CI for experimental values | Dose Reduction Index (DRI) | |||||
|---|---|---|---|---|---|---|
| IR (Gy) | fa | CI (point #) | Degree of syn./antag. | Vitamin D | IR | |
| (A) Vitamin D (nM) | ||||||
| 0.1 | 1 | 0.34 | 0.85 (1) | + | 3.77 | 2.18 |
| 1 | 2 | 0.60 | 0.57 (2) | +++ | 9.46 | 2.36 |
| 10 | 4 | 0.74 | 0.76 (3) | ++ | 6.70 | 1.89 |
| 100 | 4 | 0.75 | 2.43 (4) | −−− | 0.79 | 1.96 |
| (B) Zemplar (nM) | Zemplar | |||||
| 0.1 | 1 | 0.45 | 1.27 (1) | −− | 2.08 | 1.88 |
| 1 | 2 | 0.79 | 0.45 (2) | +++ | 10.81 | 3.05 |
| 10 | 4 | 0.89 | 0.54 (3) | +++ | 7.85 | 2.75 |
| 100 | 4 | 0.86 | 4.22 (4) | −−−− | 0.39 | 2.23 |
CI values for each combination treatment at doses shown on the left were calculated with the CalCuSyn software as described in Materials and Methods. CI values correspond to points shown in the isobolograms depicted in Figure 3. The DRI for each drug:IR combination is a measure of how much (-fold) the dose of a drug or agent (e.g. IR) is synergistic combination may be reduced at a given effect level compared with the dose of each drug alone. The DRI is another mathematical interpretation of the CI, and CI=1/(DRI)1+1/(DRI)2. +++++, very strong agonism; −−−−− very strong antagonism