Thyroid scanning using technetium-99m (99mTc) is the gold standard for diagnosing feline hyperthyroidism. In cats with an overactive thyroid, a thyroid scan is the most appropriate imaging technique to detect and localize any hyperfunctional adenomatous thyroid tissue. In this study, the pharmacological properties of the Technekitty injection (Tc-99m), developed as a diagnostic agent for feline hyperthyroidism using 99mTc as an active ingredient, were tested in FRTL-5 thyroid follicular cell line and ICR mice. The percentage of cell uptake of the Tc-99m in FRTL-5 thyroid cells was 0.182 ± 0.018%, which was about 6 times higher compared to Clone 9 hepatocytes. This uptake decreased by 38.2% due to competitive inhibition by iodine (sodium iodide). In tissue distribution tests by using ICR mice, the highest distribution was observed in the liver, kidneys, spleen, lungs, and femur at 0.083 hours after administration, and this distribution decreased as the compound was excreted through the kidneys, the primary excretory organ. Maximum distribution was confirmed at 1 hour in the small intestine, 6 hours in the large intestine, and 2 hours in the thyroid gland. Additionally, the total amount excreted through urine and feces over 48 hours (2 days) was 78.80% of the injected dose, with 37.70% (47.84% of the total excretion) excreted through urine and 41.10% (52.16% of the total excretion) through feces. In conclusion, the Tc-99m has the same mechanism of action, potency, absorption, distribution, metabolism, and excretion characteristics as 99mTc used for feline hyperthyroidism in the United States, Europe, and other countries, because the Technekitty injection (Tc-99m) contains 99mTc as its sole active ingredient. Based on these results, the Technekitty injection (Tc-99m) is expected to be safely used in the clinical diagnosis of feline hyperthyroidism.

Abstract
INTRODUCTION
MATERIALS AND METHODS
    시험물질의 품질 확인 시험
    세포 배양
    세포 섭취율 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
    조직 분포 및 배설 시험을 위한 시험물질의 제조 및 투여
    생체 내 조직 분포 시험; 각 시간대별 조직 내 분포(%injected dose/organ)
    생체 내 조직 분포 시험; 각 시간대별 조직 내 분포(%injected dose/g)
    생체 내 조직 분포 시험; 조직 내 분포(%injected dose/g)의 PK 파라미터(parameter) 산출
    생체 내 배설 시험
DISCUSSION
SUPPLEMENTARY MATERIALS
References

• Jae Cheong Lim(Radioisotope Research Division, Korea Atomic Energy Research Institute, Daejeon 34057, Korea) Corresponding author
• So-Young Lee(Radioisotope Research Division, Korea Atomic Energy Research Institute, Daejeon 34057, Korea)
• Eun Ha Cho(Radioisotope Research Division, Korea Atomic Energy Research Institute, Daejeon 34057, Korea)
• Yu Mi Jung(Radioisotope Research Division, Korea Atomic Energy Research Institute, Daejeon 34057, Korea)
• Ki Hwan Park(Radioisotope Research Division, Korea Atomic Energy Research Institute, Daejeon 34057, Korea)
• Young Uk Park(Radioisotope Research Division, Korea Atomic Energy Research Institute, Daejeon 34057, Korea)
• Sung Soo Nam(Radioisotope Research Division, Korea Atomic Energy Research Institute, Daejeon 34057, Korea)
• Tae Hoon Lee(Radioisotope Research Division, Korea Atomic Energy Research Institute, Daejeon 34057, Korea)
• Jae Won Lee(Radioisotope Research Division, Korea Atomic Energy Research Institute, Daejeon 34057, Korea)
• Jisu Sun(Korea Radioisotope Center for Pharmaceuticals, Korea Institute of Radiological and Medical Sciences, Seoul 01812, Korea)
• Hye Kyung Chung(Korea Radioisotope Center for Pharmaceuticals, Korea Institute of Radiological and Medical Sciences, Seoul 01812, Korea)
• Yong Jin Lee(Korea Radioisotope Center for Pharmaceuticals, Korea Institute of Radiological and Medical Sciences, Seoul 01812, Korea)
• Yeon Chae(Laboratory of Veterinary Internal Medicine, College of Veterinary Medicine, Chungbuk National University, Cheongju 28644, Korea)
• Byeong-Teck Kang(Laboratory of Veterinary Internal Medicine, College of Veterinary Medicine, Chungbuk National University, Cheongju 28644, Korea)