Use of Potassium Iodide (KI) in a Nuclear Emergency

Abstract

Medicine for Policymakers is a Journal column that provides decision makers with brief explanations of the meaning and implications for biosecurity of clinical issues. The articles describe, for a nonmedical audience, hospital practices, medical challenges, healthcare delivery issues, and other topics of current interest. Readers may submit ideas to the column's editor, Amesh A. Adalja, MD, through the Journal's editorial office at jfox@upmc-biosecurity.org.

Iodine is a natural element that is essential for life. Its principal function is as a component of the thyroid hormones that regulate metabolism and are made by the thyroid gland. Normally, iodine from food is absorbed into the blood through the intestine and then extracted by the thyroid gland and concentrated there for use in hormone production.¹

A radioactive isotope of iodine (I-131, radioiodine) is one of the byproducts of the nuclear fission of plutonium or uranium, which occurs in a nuclear reactor's core. Environmental release of I-131 from a nuclear power plant or other nuclear reactor poses a threat to human health primarily because it is associated with an increased risk for the development of a thyroid cancer in children. The thyroid cannot distinguish I-131 from normal iodine, and, if I-131 is absorbed into the blood, the gland will concentrate and store it. The radioactive emissions from the concentrated I-131 in the thyroid tissue can damage the thyroid cells' DNA, leading in some cases to thyroid cancer.¹

Human exposure to I-131 after a release occurs through inhalation of I-131 suspended in the air and/or ingestion of contaminated milk, vegetables, or water. For the most part, the inhalational pathway of exposure is only of significance close to the source of the release: The EPA estimates this distance to be no more than a 10-mile radius surrounding a nuclear power plant. Ingestion can occur over a wider area (50 miles). I-131 has a relatively short radioactive half-life of about 9 days—that is, in 9 days half the radiation has dissipated, and in 90 days essentially all the radiation is gone.¹

The Chernobyl Experience

The Chernobyl accident has been the chief source of data regarding human exposure to radioiodine. In the years following that catastrophic release of radiation, approximately 5,000 cases of thyroid cancer in children and young adults were attributed to the I-131 exposures.² Consumption of food and water that had been contaminated with radioiodine, rather than inhalation, was thought to be the primary route of radioiodine exposure.¹

It is important to note that in the Chernobyl fall-out zone there was a high prevalence of iodine deficiency. People with iodine deficiency take up iodine, including I-131, more avidly than those with normal iodine levels and, therefore, have a greater risk of thyroid cancer. Iodine deficiency is rare in the U.S. and other developed countries, so the expected rate of radioiodine uptake, and thus thyroid cancer, would be lower than in Chernobyl.¹ Additionally, modeling of U.S. nuclear power plant accidents estimates a much lower amount of I-131 would be released than occurred at Chernobyl because of plant design differences.¹

For U.S. planning purposes, the ingestion pathway is considered to be relatively less important because the Food and Drug Administration (FDA) and the Environmental Protection Agency (EPA) have safeguards in place to prevent consumption of contaminated products and water.

Potassium Iodide Blocks Absorption of I-131

Potassium iodide (KI) is a pharmaceutical product that was approved by the FDA in December 1978 for use in blocking the uptake of I-131 by the thyroid gland after an environmental release. The use of KI decreases the risk of the development of a subsequent thyroid cancer by saturating the thyroid gland with iodine and rendering it unable to absorb carcinogenic I-131. KI is available over the counter, and 3 formulations are currently commercially available in the U.S.:³

1. Iosat, manufactured by Anbex, Inc.

2. Thyrosafe, manufactured by Recip

3. Thyroshield, manufactured by Fleming

KI products generally have a 2- to 3-year shelf life, but with appropriate storage conditions this can be extended to 7 years.¹ On a major drug retailer's website, the cost is approximately 70 cents per tablet.

All evidence points to KI's effectiveness being limited exclusively to children, including fetuses exposed in utero or infants exposed via breast milk. There is no appreciable risk for thyroid cancer in adults after radioiodine exposure, although there is equivocal evidence of a slight risk that extends to age 30.^1,4,5

For KI to be most effective, it should be ingested a few hours prior to exposure. Its ability to protect the thyroid diminishes as the time to exposure decreases, and it diminishes when KI is administered postexposure. On the other hand, KI is also ineffective if given too early before an exposure (more than 48 hours).¹

The FDA guidance specifies that KI be taken when the predicted thyroid exposure is 50 mSv for children, pregnant women, and breastfeeding women; 100 mSv for adults between 18 and 40 years; and >5 Sv for those above age 40, solely to prevent radiation-induced hypothyroidism.⁴

Side effects of KI include gastrointestinal distress (nausea, vomiting, and diarrhea) and rash, which occur at a rate of 1% to 2%. Allergic reactions are also possible. Additionally, transient iodine-induced hypothyroidism—underactive thyroid function—is possible, especially in infants.¹

Current KI Planning

Current U.S. planning for the use of KI is primarily a state issue. Thirty-three states fall within the federal government's 10-mile emergency planning zone (EPZ) for the 104 nuclear reactors in the U.S. KI has been available over the counter since 1978, and between that time and 2001 only 3 of the states had incorporated KI into their planning efforts. More recently, the Nuclear Regulatory Commission (NRC) has offered to provide KI to states that request it for their population within the 10-mile EPZ. Currently, 24 of the 33 states use KI in their state plans. States within the 10-mile EPZ that do not have KI plans are Arkansas, Georgia, Iowa, Kansas, Louisiana, Missouri, Nebraska, Texas, and Washington.

Neither the Federal Emergency Management Agency (FEMA) nor the NRC mandates the use of KI in state planning efforts, but the NRC notes that its use “should be considered for the general public within the 10-mile EPZ of a nuclear power plant” as a supplement to other activities (ie, sheltering in place, evacuation, etc). KI is also a component of the Strategic National Stockpile (SNS) and is available in the event of an emergency to states and local governments who do not stockpile KI.^1,6

Some states have decided not to incorporate KI into their emergency plans. Their reasons, listed in state planning documents, include: (1) KI distribution may interfere with more important activities, such as sheltering and prompt evacuation, especially since radioiodine is not the only material of concern released in a nuclear event and KI provides no protection apart from radioiodine; and (2) KI could provide the public with a false sense of security, whereas evacuation provides definitive protection from radiation.¹ Other reasons may exist.

Three Mile Island and Fukushima

Despite the limited role of KI, nuclear events of varying magnitudes incite a heightened demand for KI that may put stress on responders, pharmacies, and physicians. During the partial meltdown that occurred at Pennsylvania's Three Mile Island (TMI) nuclear facility in 1979, despite radioiodine concentrations at 0.003 (0.3%) of the concentration at which the FDA recommends removal of cows from contaminated pastures, 250,000 bottles of KI were sent to TMI in what was termed a “crash effort.” Because its use was not indicated, it was not administered to any individuals.^7,8

In 2011, after the meltdown at Japan's Fukushima nuclear plant, the U.S. Surgeon General stated that purchasing of KI by mainland residents of the U.S. was “definitely appropriate.” Sales of KI increased in the U.S., and military personnel were administered KI.⁹ Additionally, the SNS was preparing to donate doses of KI to Japan, but the request did not occur.

Reexamining KI Policy

Demand for KI can be anticipated to be high in any future event, despite the lack of evidence of its efficacy for those other than children, pregnant women, and breastfeeding women who are administered the medication within a strict time period. Public understanding of the scientific basis for KI's use—and its limitations—are essential so that the medication can be used appropriately while not delaying the implementation of other mitigation activities (ie, evacuation) that will protect against all radionuclides.

References

Committee to Assess the Distribution and Administration of Potassium Iodide in the Event of a Nuclear Incident, National Research Council. Distribution and Administration of Potassium Iodide in the Event of a Nuclear Incident. Washington, DC: National Academies Press, 2004.

World Health Organization. Health effects of the Chernobyl accident: an overview. http://www.who.int/mediacentre/factsheets/fs303/en/index.html. 2011 August 4.

U.S. Food and Drug Administration. Frequently Asked Questions on Potassium Iodide (KI) http://www.fda.gov/Drugs/EmergencyPreparedness/BioterrorismandDrugPreparedness/ucm072265.htm. 2011 August 4.

U.S. Food and Drug Administration. Potassium Iodide as a Thyroid Blocking Agent in Radiation Emergencies. http://www.fda.gov/downloads/Drugs/GuidanceComplianceRegulatoryInformation/Guidances/UCM080542.pdf. 2011 August 17.

Cardis

, Hatch

. The Chernobyl accident—an epidemiological perspective. Clin Oncol, 2011; 23:251–260.

U.S. Nuclear Regulatory Commission. Frequently Asked Questions on Potassium Iodide. http://www.nrc.gov/about-nrc/emerg-preparedness/about-emerg-preparedness/potassium-iodide/ki-faq.html. 2011 August 4.

Scranton

II . Report of the Governor's Commission on Three Mile Island. Commonwealth of Pennsylvania. http://www.threemileisland.org/downloads//199.pdf. 2011 August 4.

Federal Radiological Emergency Preparedness Committee. Interagency Technical Evaluation Paper for Section 127(f) of the Bioterrorism Act of 2002. http://www.whitehouse.gov/sites/default/files/microsites/ostp/ki-evaluation-2007.pdf. 2011 August 4.

Gever

. Japan reactor crisis triggers run on iodide pills on west coast. MedPage, March 15, 2011. http://www.medpagetoday.com/PublicHealthPolicy/EnvironmentalHealth/25352. 2011 August 4.