Combinations of arabinosyl cytosine and 6‐thioguanine for treatment of adults with acute leukemia

The combination of arabinosyl cytosine and 6‐thioguanine has been effective for the treatment of acute leukemia. Three schedules of this combination were studied to determine which was most effective, especially in patients who had prior exposure to either or both of these drugs. Sequential and simultaneous 5‐day courses of the combination were ineffective. A regimen consisting of a 5‐day course of arabinosyl cytosine followed by a 5‐day course of 6‐thioguanine and another 5‐day course of arabinosyl cytosine produced responses in 36% of 25 patients. Seven of the nine patients who responded were refractory to prior therapy with arabinosyl cytosine and 5 were refractory to prior therapy with 6‐mercaptopurine. However, the median duration of response was only six weeks. Four patients developed central nervous system complications and three of these patients died while in complete remission. Major toxicity from all three regimens was myelosuppression. This regimen was about as effective as most other regimens used as secondary therapy in patients with acute myelogenous leukemia, but its toxicity was too great for routine usage.