Timing- and sequence-dependent synergism between etoposide and methotrexate or etoposide, methotrexate and 5-fluorouracil in advanced leukemia L1210.

The optimal synergism in combination therapy of leukemia L1210 depends on the sequence and the timing of the agents used. Etoposide (20 mg/kg applied intravenously) 3 h before methotrexate (50 mg/kg administered subcutaneously) results in significantly improved therapeutic action. Simultaneous application of these drugs, or an exceeding of that interval, do not entail synergism. Similar to the results obtained with other transplantable murine tumors, the optimal interval between methotrexate and 5-fluorouracil treatments of leukemia L1210 amounts to 6 h. Sequential treatment with etoposide (20 mg/kg given intravenously) significantly improves the efficacy of combined methotrexate (50 mg/kg applied subcutaneously) and 5-fluorouracil (80 mg/kg administered subcutaneously). The optimal synergism combining etoposide, methotrexate and 5-fluorouracil is achieved when the interval between etoposide and methotrexate amounts to 3 h followed 6 h later by 5-fluorouracil.