Introduction

The fluoropyrimidine 5-fluorouracil (5-FU) is infrequently used to manage tumors in veterinary oncology. Teysuno (TS-1) is an oral fixed-dose combination of three active substances—tegafur, gimeracil, and oteracil. After absorption, tegafur is metabolized into 5-FU. This combination is intended to minimize toxicity. The purpose of this study was to evaluate the safety of Teysuno in dogs with solid tumors.

Methods

A regimen of 2.5 mg/kg BID was administered to each dog with solid tumors on alternating days (Monday—Wednesday—Friday).

Results

Nine dogs were included. The initial dose of TS-1 (mean ± SD) was 2.3±0.5 mg/kg administered BID three days (M-W-F) per week. The median administration period was 67 days (range, 14–491 days). Cause of discontinuation was death (n=3), decreased QOL due to adverse events (n=3), and tumor progression (n=3). Tumor response was noted PR (n=1), SD (n=1), PD (n=5), and not assessed (n=2). Other beneficial effects were noted in one dog: seizures were controlled for 49 days. Adverse events were noted in 5 dogs, including scleral pigmentation (n=4), anorexia related to olfactory loss (n=2), skin pigmentation (n=2), diarrhea (n=1), increased T-Bil (n=1), and opacified cornea (n=1).

Conclusion

Teysuno was safe in tumor bearing dogs, and adverse events were mild. Efficacy was detected in some cases. Therefore, it may be a viable option for treating malignant solid tumors in dogs.

Funding Information

No funding was used for this project.