[Oral single-dose toxicity study of a new antineoplastic agent S-1, and its components, CDHP, and Oxo]

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 produced by FT alone and reducing its dose-limiting gastrointestinal toxicity. As a part of the S-1 toxicity study, the single-dose toxicity of S-1 as well as that of its components, CDHP and Oxo, was investigated in mice, rats, and dogs. The following results were obtained. 1. In mice and rats, excretion of diarrheal stools, salivation, and alopecia were observed after S-1 administration. In severe cases, the animals subsequently showed emaciation due to weight loss or suppressed weight gain, decreased spontaneous motor activity, an anemic appearance, bradypnea, prone position, and death. In the CDHP and Oxo treatment groups of rats, the only toxic signs were soft or diarrheal stools on the dosing day. 2. In dogs, vomiting and excretion of diarrheal, mucous, or soft stools was observed after S-1 administration. In the CDHP and Oxo treatment groups, excretion of soft and diarrheal stools and vomiting were observed relatively frequently from the dosing day until day 1. 3. In the pathological examination of the animals given S-1, mice and rats showed pulmonary congestion/edema, dark red discoloration of the mesenteric lymph nodes, atrophy of lymphatic tissues such as the thymus and lymph nodes, decreases of lymphocytes in the splenic white pulp and mesenteric lymph nodes, a decrease in bone marrow cells, congestion of the glandular stomach, and aggregates of bacteria in the lung, liver, or spleen. In dogs, abnormal changes were observed mainly in the lymphatic organs such as the thymus and lymph nodes. 4. The LD50 values of S-1 in terms of the amount FT they contained were estimated to be 549 mg/kg for mice(male), 441-551 mg/kg for rats (both sexes) and about 53 mg/kg for dogs (male). The LD50 values of CDHP and Oxo were 2000 mg/kg or higher for both rats (both sexes) and dogs (male). 5. Hematopoietic and lymphatic impairments, immunosuppression associated with respiratory were considered to be the cause of death from S-1. The toxicity of S-1 reflects the toxicity of 5-FU and was not found the different toxicity by the addition of CDHP and Oxo.