Cell population size dependency of therapeutic effect of divided dosage of 1-beta-D-arabinofuranosylcytosine.

A total dose of 960 mg/kg body weight of 1-beta-D-arabinofuranosylcytosine (cytosine arabinoside) was given intraperitoneally to rats bearing Yoshida sarcoma, in a single or divided doses. Single-dose therapy gave an increased life span of about 1 day irrespective of cell population size in accord with the concept of constant percentage cell kill. Tumor cell reduction was estimated to be about 70%. Divded-dose therapy, however, brought about increased life span which was reciprocally proportional to the logarithm of population size. Estimated cell reduction was 87% when population size was 10(8) cells and 99.95% at 10(4) cells.