The antileukemic effectiveness of 5-fluorouracil and methotrexate in the combination chemotherapy of advanced leukemia L1210 in mice.

Enchanced therapeutic effectiveness has been demonstrated by combining methotrexate and 5-fluorouracil in the treatment of murine leukemia L1210. Optimal combinations of the 2 drugs consistently showed greater antileukemic activity than optimal treatment with each drug by itself. The treatment schedules resulting in this enhanced activity were characterized by rela tively low and therapeutically ineffective doses of 5-fluorouracil, whereas the associated level of methotrexate ranged from slightly less than optimal to optimal. The therapeutic activity of the combination of the drugs was limited by the development of host toxicity similar to that observed when the drugs were used by themselves.