Radioiodine (131I) has been used for the treatment of feline hyperthyroidism since the 1990s in the USA and Europe, and it is recommended as the most effective treatment for feline hyperthyroidism because it has a high therapeutic effect, small side effects, and does not require anesthesia. In this study, the pharmacological properties of the Thyrokitty injection (I-131), which is being developed as a treatment for feline hyperthyroidism, using radioiodine (131I) as an active ingredient, was tested. The %cell uptake of the Thyrokitty injection (I-131) in FRTL- 5 thyroid cells was 0.410 ± 0.016%, which was about 18 times higher compared to Clone 9 hepatocytes, and it was decreased by 30.7% due to the competitive reaction with iodine (sodium iodide). In addition, the %cell growth of the FRTL-5 thyroid cells was reduced by 25.0% by treatment with the Thyrokitty injection (I-131). As a result of the tissue distribution test, the Thyrokitty injection (I-131) was distributed at the highest concentration at 0.083 hours (5 minutes) after subcutaneous administration to animals in most organs except the stomach, small intestine, large intestine, muscle and thyroid gland, and it was excreted mainly through the kidneys. The stomach and thyroid gland showed a typical distribution pattern observed when radioiodine (131I) was administered. In addition, about 78.45% of the total amount of excretion was excreted within 48 hours, of which more than 85% was excreted in urine. In conclusion, the Thyrokitty injection (I-131) has the same mechanism of action, potency, absorption, distribution, metabolism and excretion characteristics as radioiodine (131I) reported in connection with the treatment of feline hyperthyroidism. In the future, using the results of this study, it is expected that the Thyrokitty (I-131) could be safely used in the clinical treatment of feline hyperthyroidism.

Abstract
INTRODUCTION
MATERIALS AND METHODS
    시험물질의 품질 확인 시험
    세포 배양
    세포 섭취율 시험
    세포 사멸 효과 시험
    실험동물 사육 관리
    조직 분포 및 배설 시험을 위한 시험물질의 제조 및 투여
    생체 내 조직 분포 시험
    생체 내 배설 시험
    통계 분석
RESULTS
    시험물질의 품질 확인
    세포 섭취율 평가
    세포 사멸 효과 평가
    조직 분포 및 배설 시험을 위한 시험물질의 제조 및 투여
    생체 내 조직 분포 시험; 각 시간대별 조직 내 분포(%ID/organ)
    생체 내 조직 분포 시험; 각 시간대별 조직 내 분포(%ID/g)
    생체 내 조직 분포 시험; 조직 내 분포(%ID/g)의 약동학적 파라미터(PK parameter) 산출
    생체 내 배설 시험
DISCUSSION
SUPPLEMENTARY MATERIALS
REFERENCES

• Jae Cheong Lim(Radioisotope Research Division, Korea Atomic Energy Research Institute) Corresponding author
• Da Mi Kim(Radioisotope Research Division, Korea Atomic Energy Research Institute)
• Sung Soo Nam(Radioisotope Research Division, Korea Atomic Energy Research Institute)
• Eun Ha Cho(Radioisotope Research Division, Korea Atomic Energy Research Institute)
• So-Young Lee(Radioisotope Research Division, Korea Atomic Energy Research Institute)
• Hye Kyung Chung(Korea Radioisotope Center for Pharmaceuticals, Korea Institute of Radiological and Medical Sciences)
• Inki Lee(Korea Radioisotope Center for Pharmaceuticals, Korea Institute of Radiological and Medical Sciences)