Evaluation in a mouse model of a thyroid-blocking protocol for 131I antibody therapy (short communication)

Purpose: We describe a murine model to evaluate variations of a published multicenter thyroid blocking protocol described for I-131 antibody therapy, using doses of blocking agents proportional to those used in man. Variables include duration of super-saturated potassium iodide (SSKI) pretreatment and use of supplemental KClO4. Materials and Methods: Whole-body activity measurements were performed 0, 24, 48 and 72 hows following I-131-NaI administration in control and thyroid-blocked mice. Retained whole-body activity was calculated as a percentage of the injected dose (%ID), primarily reflecting radioiodine sequestered in the thyroid gland. In blocked groups, SSKI was begun one or 7 days preceding I-131-NaI therapy, and was supplemented in one half of the cases with KClO4 from time of therapy. Results: In control mice, %ID was 11.23+/-1.47%, 10.15+/-1.11% and 9.29+/-1.50% at 24, 48 and 72 hrs respectively. %IDs of blocked groups were markedly lower than controls (p=.0001). In the one day SSKI pretreatment group, %ID was reduced from 1.73+/-0.58, 1.42+/-0.45 and 1.20+/-0.38 at 24, 48 and 72 hours to 0.49+/-0.08, 0.50+/-0.07 and 0.44+/-0.06 with addition of supplemental KClO4. In the 7 day SSKI pretreatment group, %ID was reduced from 1.87+/-0.73, 1.48+/-0.49 and 1.36+/-0.57 at 24, 48 and 72 hours to 0.60+/-0.36, 0.45+/-0.13 and 0.41+/-0.14 with addition of supplemental KClO4. %IDs in the 7 day pretreatment animals were not statistically different from those in the one day pretreatment groups (all p>>0.05). Conclusion: SSKI reduces retention of radioiodide approximately six-fold whereas supplemental KClO4 enhances thyroid blocking an additional three-fold. Seven day SSKI pretreatment appears no more effective than one day pretreatment.