Repeated KI prophylaxis in case of prolonged exposure to iodine radioisotopes: pharmacokinetic studies in adult rats

International audiencePurpose To propose a new and effective dose regimen for stable potassium iodide (KI) repeated prophylaxis in case ofprolonged exposure to radioactive iodine.Methods The pharmacokinetics of iodine was determined in rats by compartmental analyses after intravenous and oral administrations of the optimal dose of 1 mg/kg KI, which was previously selected in a dose-effect study. The thyroid protection against iodine-125 incorporation was followed during 24 h after a single oral dosing of KI. A repeated KI prophylaxis was modeled using initial estimates of iodine pharmacokinetic parameters.Results A dose regimen consisting in administrations of 1 mg/kg daily for 8 days was selected and studied. Plasma iodine concentrations predicted by simulation were verified by experimental data and varied after the third dose of KIbetween 174 and 1190 μg/l. The inhibition study of iodine-125 binding in the thyroid as a function of the time showedthat the protection effect of KI could be correlated to stable iodine plasma concentrations. Hence, a theoretical decreasein iodine-125 thyroid uptake from 63 to 88% could be achieved in a 24 h-interval between two KI doses.Conclusion Given the satisfactory levels of thyroid protection, this dose regimen could be envisaged in order to extent KI indications for repeated prophylaxis