coefficient of drug interaction (CDI)
CDI was used to calculate synergy with the combination using mean tumor weight measurements:
CDI = AB/(A×B)
where AB is the ratio of the 2-drug combination group to the control group and A or B is the ratio of the single drug group to the control group.
- CDI < 1 indicates synergism
- especially CDI < 0.7 indicates a significantly synergistic effect
- CDI = 1 indicates additivity
- CDI > 1 indicates antagonism.