Table 3. Dose reduction index (DRI) values for CDDP in combination with cinobufagin.

Cell line	Drug:compound	Molar ratio (CDDP:cinobufagin)	DRI(75% fraction affected level)
143B	CDDP:Cinobufagin	1:30	7.207

The DRI signifies the fold decrease of CDDP as a result of synergistic combination in compared with the concentration of a single agent needed to achieve the same effect. Concentrations of CDDP were reduced∼7 folds in 143B to achieve a 75% inhibition of cell proliferation when the cells were exposed to combination treatment at fixed molar ratios after 48 h.