The Food and Drug Administration has issued a guidance on the use of potassium iodide (KI) to reduce the risk of thyroid cancer in children and adults in emergencies involving the release of radioactive iodine into the environment.
The document advises other federal agencies and state and local governments on safe and effective dosages of KI as an addition to other protective measures, such as evacuation, sheltering, and assurance of uncontaminated food and milk for infants and children, who are most susceptible to radiation-induced thyroid cancer.
The FDA guidance, which was developed in collaboration with experts from the National Institutes of Health, supersedes recommendations issued by the agency in 1978 and 1982. At that time, the FDA was guided mostly by studies on the risk of thyroid disease that used estimates of external thyroid irradiation resulting from the WWII nuclear detonations in Hiroshima and Nagasaki. The agency's new recommendations are derived from a review of the much more comprehensive and reliable data in studies conducted after the Chernobyl nuclear reactor accident in April 1986.
These studies included measurements of thyroid exposure to radiation in hundreds of thousands of children and other individuals in Ukraine, Belarus and the Russian Federation. The studies also provided information about the large-scale use of KI in Poland, where it was administered to millions of children and adults affected by the Chernobyl radiation fallout.
The data clearly demonstrate the risks associated with thyroid radiation from radioiodines that are inhaled or ingested with contaminated food. When such exposures are likely, KI can be used to block thyroid uptake of radioactive iodine species and thus provide safe and effective protection against thyroid cancer caused by such irradiation when exposure can not be prevented by other measures.
Based on the data related to the Chernobyl accident, FDA recommends a standard daily dose of 16 mg of KI for infants less than one month old; 32 mg of KI to children aged one month to three years; 65 mg of KI for children and teenagers from three years to 18 years old; and 130 mg of KI for adults, including pregnant and lactating women, and adolescents over 150 lbs.
As a rule, daily dosing should continue until the risk of exposure has passed and/or until other measures (evacuation, sheltering, control of the food and milk supply) have been successfully implemented. The increased risk of thyroid suppression in the fetus and neonate leads to a specific recommendation that newborns and pregnant women be given priority with regard to these adjunctive measures in order to obviate, as possible, the need for repeat dosing with KI.
The guidance acknowledges that strict adherence to the recommendations above and to age-related dosing guidelines may be difficult to achieve and, therefore, emphasizes that across populations at risk for radioiodine exposure, the overall benefits of KI far exceed the risks of overdosing, especially in children, though particular attention should be paid to dose and duration of treatment in infants and in pregnant women.
Guidance on using potassium iodide to reduce the risk of thyroid cancer in children and adults in emergencies involving the release of radioactive iodine into the environment