A 13-WEEK ORAL REPEATED DOSE TOXICITY STUDY OF A NEW ANTINEOPLASTIC AGENT S-1 IN RATS

S-1, an antineoplastic formulation of a fluorinated pyrimidine derivative containing tegafur (FT), CDHP, and potassium oxonate (Oxo) in a molar ratio of 1:0.4:1, was recently developed by Taiho Pharmaceutical Co., Ltd., with the aim of prolonging the effective plasma concentration of 5-fluorouracil (5-FU) over that producted by FT alone and reducing its dose-limiting gastrointestinal toxicity. As a part of the S-1 toxicity study, a 13-week oral repeated dose toxicity study and a recovery study using male and female rats was conducted. Doses of S-1 were adjusted to deliver 1.5, 5, and 15 mg/kg/day as doses of FT, and FT wad given at 15mg/kg/day. The following results were obtained. 1. In clinical observation, edema of the limbs and face or swelling of the auricle of the ear and an anemic appearance were observed in both sexes in the 15 mg/kg/day group as dose of FT. Subsequently, ma1es in ithis group developed severe anemia, decrdased spontaneous motor activity, emaciation, and subnormal skin temperature, and many males died. In the survivors, keratosis of the palm, sole, or tail was observed, with necrosis and loss of the tail tip in the severe cases. 2. Body weight gain was suppressed from about week 2 of treatment in both sexes in the 15 mg/kg/day group as dose of FT, and there was almost no weight gain after week 4-5. Food consumption was consistently less than the control value for males in the 15 mg/kg/day group as dose of FT throughout the treatment period. 3. No marked changes were observed in water intake and on ophthalmologic examination. 4. In the fecal test for occult blood, a positive tendency was observed in both sexes in the 15 mg/kg/day group as dose of FT. 5. Urinalysis disclosed a slight increase in protein and decrease in sodium, potassium, and chloride in males, and an increase in protein in females in the 15 mg/kg/day group as dose of FT. 6. Hematologically, both sexes in the 15 mg/kg/day group as dose of FT showed decreases in red blood cell count, hemoglobin, and hematocrit, and increases in platelet count and fibrinogen, with a slight decrease in white blood cell count in males. 7. In the blood biochemical test, abnormal findings included increases in total cholesterol and free cholesterol, and decreases in non-esterified fatty acid and albumin in both sexes in the 15 mg/kg/day group as dose of FT. 8. In organ weight measurement, abnormal changes included a decrease in thymus weight in both sexes in the 5 mg/kg/day or higher dosage g