Solid tumour models for the assessment of different treatment modalities: VII: single vs fractionated doses of 5-fluorouracil on two solid tumours and their hosts.

The effects of one large single dose of 5-fluorouracil (FU) have been compared to the same amount given in divided doses daily over a 3- or 5-day period. Comparison of the effects of single vs fractionated dosage was made on 2 types of experimental solid tumour with different growth, cell kinetic, histological and metastasizing properties. The tumour response was essentially the same for both the single and fractionated dose schedules.There were marked increases in animal mortality from drug toxicity following fractionated doses of FU compared to one large single dose. Mortality in animals with Tumour 3924A increased from 10% following one large single dose to 60% for animals given daily fractionated doses for 3 days, and 80% for animals given daily fractionated doses for 5 days. Total marrow reserve was measured by the total DNA content of tibial marrow. The nadir of 6 days for loss of total tibial marrow DNA following one large dose of FU was increased to 9 days for both fractionated schedules of FU. The 3-day delay in recovery of the marrow prevented recovery within the time frame necessary for animal survival. The inference from these experimental cancer-treatment studies is that daily fractions of chemotherapeutic agents such as FU result in increased morbidity and mortality, without benefit in the control of the solid tumour. The results question the advisability of the clinical practice of initially giving small daily "loading doses" of proliferation-dependent agents such as FU.These results emphasize the need for more precise information on the temporal relationship between the response and recovery of the host and the response and recovery of the solid tumour. They also emphasize the need for a better clinical understanding of the time sequence of solid-tumour recovery in relation to the time sequence of marrow recovery.