Protection and safety of a repeated dosage of KI for iodine thyroid blocking during pregnancy.

In case of nuclear power plant accidents resulting in the release of radioactive iodine (131I) in large amounts, a single intake of stable iodine is recommended in order to prevent131I fixation to the thyroid gland. However, in situations of prolonged exposure to131I (e.g. Fukushima-Daiichi natural and nuclear disaster), repetitive administration of iodine may be necessary to ensure adequate protection, with acceptable safety in vulnerable populations including pregnant women. Here we conducted toxicological studies on adult rats progeny following prolonged exposure to potassium iodide (KI)in utero. Pregnant Wistar rats were treated with 1 mg kg d-1KI or saline water for 2 or 4 d either between gestation days gestational day (GD) GD 9-12, or GD13-16. Plasma samples from the progeny were tested 30 d post-weaning for clinical biochemistry, thyroid hormones, and anti-thyroid antibody levels. Thyroid and brain were collected for gene expression analysis. The hormonal status was similar for the mothers in all experimental conditions. In the offspring, while thyroid-stimulating hormone and anti-thyroid peroxidase (anti-TPO) antibody levels were similar in all groups, a significant increase of FT3 and FT4 levels was observed in GD9-GD10 and in GD13-GD14 animals treated for 2 d, respectively. In addition, FT4 levels were mildly decreased in 4 d treated GD13-16 individuals. Moreover, a significant decrease in the expression level of thyroid genes involved in iodide metabolism, TPO and apical iodide transporter, was observed in GD13-GD14 animals treated for 2 d. We conclude that repeated KI administration for 2-4 d during gestation did not induce strong thyroid toxicity.

Review of the PRIODAC project on thyroid protection from radioactive iodine by repeated iodine intake in individuals aged 12.

BACKGROUND: Intake of potassium iodide (KI) reduces the accumulation of radioactive iodine in the thyroid gland in the event of possible contamination by radioactive iodine released from a nuclear facility. The WHO has stated the need for research for optimal timing, appropriate dosing regimen and safety for repetitive iodine thyroid blocking (ITB). The French PRIODAC project, addressed all these issues, involving prolonged or repeated releases of radioactive iodine. Preclinical studies established an effective dose through pharmacokinetic modeling, demonstrating the safety of repetitive KI treatment without toxicity. SUMMARY: Recent preclinical studies have determined an optimal effective dose for repetitive administration, associated with pharmacokinetic modelling. The results show the safety and absence of toxicity of repetitive treatment with KI. Good laboratory practice level preclinical studies corresponding to individuals > 12 years have shown a safety margin established between animal doses without toxic effect. After approval from the French health authorities, the market authorization of the 2 tablets of KI-65mg/day was defined with a new dosing scheme of a daily repetitive intake of the treatment up to 7 days unless otherwise instructed by the competent authorities for all categories of population except pregnant women, and children under the age of 12 years. CONCLUSIONS: This new marketed authorization resulting from scientific-based evidence obtained as part of the PRIODAC project may serve as an example to further harmonize the application of KI for repetitive ITB in situations of prolonged radioactive release at the European and International levels, under the umbrella of the WHO.