title: Comparison of radioactive iodide uptake in the rat thyroid between oral and intravenous bolus administration.
abstract: OBJECTIVE
  Radioiodide is commonly used to diagnose and treat hyperthyroidism and thyroid carcinoma. However, we could not find any experimental data that strictly compared the biodistribution and thyroid uptake of radioactive iodide between the oral and intravenous (iv) routes with time. This prompted us to compare (123)I biodistribution and thyroid uptake to clarify the differences between oral and iv bolus administration in rats.
  
  
  METHODS
  The rats were divided into two groups, A and B (n = 5, each). In the first imaging experiment, Na(123)I solution (35 MBq/200 μL) was administered as a bolus to the rats orally in group A and intravenously in group B. Two weeks later, the second imaging experiment was performed as a crossover experiment. (123)I biodistribution was evaluated visually and quantitatively with a gamma camera at 10 min, 3, 6, 12, 24, and 48 h after (123)I administration. Thyroid uptake was compared between oral and iv groups. Correlation of (123)I thyroid uptake and whole-body excretion was evaluated. The area under the curve (AUC) of thyroid uptake was also calculated.
  
  
  RESULTS
  (123)I biodistribution differed visually during 6 h between the two groups. (123)I thyroid uptake was significantly higher in the iv group at 10 min (P < 0.05) and in the oral group at 6 or more hour time points (P < 0.005-P < 0.0001) and peaked at 12 h in both groups (oral: 24.4 ± 2.8 %ID, iv: 15.2 ± 2.8 %ID). (123)I thyroid uptake showed significant inverse correlations with whole-body excretion from 6 h (r = -0.799, P < 0.0001), and thereafter [12 h (r = -0.957, P < 0.0001), 24 h (r = -0.905, P < 0.0001) and 48 h (r = -0.893, P < 0.0001)], respectively. (123)I whole-body excretion was significantly higher in the iv group at each time point (P < 0.0001). The AUC of (123)I thyroid uptake was 1.6 times higher in the oral group than the iv group.
  
  
  CONCLUSIONS
  These results suggest that radioiodide accumulates in the rat thyroid more effectively by oral than iv administration probably due to slower and lower (123)I clearance from the body in the oral administration when administered in a bolus fashion.
authors.affiliation: Research Department, FUJIFILM RI Pharma Co., Ltd., 453-1 Shimo-okura, Matsuo-machi, Sammu, Chiba, 289-1592, Japan, khiroyuki@ffri.co.jp.
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Kurosawa
authors.forename: Kazuhisa
authors.initials: K
authors.lastname: Sakurai
authors.forename: Hideaki
authors.initials: H
authors.lastname: Hasegawa
authors.forename: Keisuke
authors.initials: K
authors.lastname: Uchida
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Kasahara
authors.forename: Takao
authors.initials: T
authors.lastname: Minamizawa
authors.forename: Masatoyo
authors.initials: M
authors.lastname: Nakajo
authors.forename: Masayuki
authors.initials: M
authors.lastname: Nakajo
mesh_terms: D000284:Administration, Oral; D000818:Animals; D019540:Area Under Curve; D018592:Cross-Over Studies; D007275:Injections, Intravenous; D007457:Iodine Radioisotopes / Q000008:administration & dosage* / Q000493:pharmacokinetics; D008297:Male; D011877:Radionuclide Imaging / Q000295:instrumentation; D019275:Radiopharmaceuticals / Q000008:administration & dosage* / Q000493:pharmacokinetics; D011897:Random Allocation; D017208:Rats, Wistar; D012974:Sodium Iodide / Q000008:administration & dosage* / Q000493:pharmacokinetics; D013270:Stomach / Q000000981:diagnostic imaging; D013961:Thyroid Gland / Q000000981:diagnostic imaging*; D013997:Time Factors
chemical_list: D007457:Iodine Radioisotopes; D019275:Radiopharmaceuticals; D012974:Sodium Iodide