CI values for combinations of ansamycin antibiotics and cytotoxic drugs. CI values for the drug combinations shown were computed under conditions where 50%, 75%, or 90% cell killing was achieved. Median CI values are shown by solid bars. The dotted lines identify CI values between 0.9 and 1.1, which were considered to indicate additive drug interactions. Values above 1.1 indicate antagonism, whereas values below 0.9 suggest synergy. (A) Chlorambucil/GA (1000:1). (B) Fludarabine/GA (100:1). (C) Chlorambucil/HMA (100:1). (D) Fludarabine/HMA (10:1).