Thyroid Blocking Agent in Radiation Emergencies

Potassium Iodide-Protects Thyroid From Radioiodine Poisoning

Downwind from a nuclear accident or detonation, most casualties result from radioactive iodine poisoning of the thyroid gland. Children are the highest risk group. Potassium iodide, if taken before exposure, reduces the threat by 95%.

Meets FDA guidelines (Dec., 2001)
300,000 doses of RAD BLOCK potassium iodide were recently purchased by Health and Human Services (HHS).

Recommended Doses of Potassium Iodide for Different Risk Groups

	Daily potassium iodide dose (mg)	# of 65mg Tablets
Adults over 40 yrs	130 mg	2
Adults over 18 through 40 yrs	130 mg	2
Pregnant or lactating women	130 mg	2
Adoles. over 12 through 18 yrs*	65 mg	1
Children over 3 through 12 yrs	65 mg	1
Over 1 month through 3 years	32 mg	1/2
Birth through 1 month	16 mg	1/4

*Adolescents approaching adult size (> 70 kg) should receive the full adult dose (130 mg).

The protective effect of potassium iodide lasts approximately 24 hours. For optimal prophylaxis, potassium iodide should therefore be dosed daily, until a risk of significant exposure to radioiodines by either inhalation or ingestion no longer exists. Individuals intolerant of potassium iodide at protective doses, and neonates, pregnant and lactating women (in whom repeat administration of potassium iodide raises particular safety issues, see below) should be given priority with regard to other protective measures (i.e., sheltering, evacuation, and control of the food supply).

Note that adults over 40 need take potassium iodide only in the case of a projected large internal radiation dose to the thyroid (>500 cGy) to prevent hypothyroidism.

These recommendations are meant to provide states and local authorities as well as other agencies with the best current guidance on safe and effective use of potassium iodide to reduce thyroidal radioiodine exposure and thus the risk of thyroid cancer. FDA recognizes that, in the event of an emergency, some or all of the specific dosing recommendations may be very difficult to carry out given their complexity and the logistics of implementation of a program of potassium iodide distribution. The recommendations should therefore be interpreted with flexibility as necessary to allow optimally effective and safe dosing given the exigencies of any particular emergency situation. In this context, we offer the following critical general guidance: across populations at risk for radioiodine exposure, the overall benefits of potassium iodide far exceed the risks of overdosing, especially in children, though we continue to emphasize particular attention to dose in infants.

Why do I need potassium iodide ?

1. Radioactive iodine (predominantly Iodine-131) is a major radioisotope constituent in nuclear power plants.
2. Radioactive iodine (predominantly Iodine-131) is also a major constituent of detonated nuclear weapons.
3. After a nuclear incident, a majority of DOWNWIND casualties that result are attributed to thyroid cancer.
4. Radioactive iodine (radioiodine) persists in the environment for a month or more.
5. Excess iodine in the blood (either radioiodine or stable Iodine), is quickly eliminated from the body, but only after the thyroid has become saturated with one or the other type of iodine.
6. Even very small amounts of radioactive iodine, because it is retained in the small space of the thyroid, eventually will give such a large radiation dose to thyroid cells there that abnormalities are likely to result.
7. The most likely to see the worst effects, in later life, are the youngest children. 8. The present threat of nuclear terrorism, including nuclear reactor threats and dirty nukes (simple radiologically-enhanced conventional explosives).

How does potassium iodide protect me ?

The recently updated (1999) World Health Organization (WHO) Guidelines for Iodine Prophylaxis following Nuclear Accidents states:

"Stable iodine administered before, or promptly after, intake of radioactive iodine can block or reduce the accumulation of radioactive iodine in the thyroid." The Nuclear Regulatory Commission (NRC) stated July 1, 1998 in USE OF POTASSIUM IODIDE IN EMERGENCY RESPONSE:

"Potassium iodide, if taken in time, blocks the thyroid gland's uptake of radioactive iodine and thus could help prevent thyroid cancers and other diseases that might otherwise be caused by exposure to airborne radioactive iodine that could be dispersed in a nuclear accident." National Council on Radiation Protection and Measurements. NCRP Report NO. 55. Protection of the Thyroid Gland in the Event of Releases of Radioiodine. August, 1979, Page 32:

"A major protective action to be considered after a serious accident at a nuclear power facility involving the release of radioiodine is the use of stable iodide as a thyroid blocking agent to prevent thyroid uptake of radioiodines.

" Federal Register. Vol. 43 Friday, December 15, 1978, states in Potassium Iodide as a Thyroid Blocking Agent in a Radiation Emergency:

"Almost complete (greater than 90%) blocking of peak radioactive iodine uptake by the thyroid gland can be obtained by the oral administration of ... iodide ...

" National Council on Radiation Protection and Measurements. NCRP Report NO. 55. Protection of the Thyroid Gland in the Event of Releases of Radioiodine. August, 1979, Page 32:

" The Nuclear Regulatory Commission (NRC) states in COMSECY-98-016 - Federal Register Notice on Potassium Iodide:

"In 1978, the U.S. Food and Drug Administration found potassium iodide"safe and effective" for use in radiological emergencies and approved its over-the-counter sale."

Recall Three Mile Island and Chernobyl.

To be effective, potassium iodide must be taken prior to radioiodine exposure. If a nuclear terrorist incident occurs, will you and your family be waiting in line to get it from the government? THINK AHEAD. Following the last several nuclear accidents, Potassium Iodide was literally impossible to purchase.

When should I take potassium iodide?

The FDA potassium iodide product insert says:

"Potassium iodide should be taken as soon as possible after public health officials tell you. You should take one dose every 24 hours.
" Also, from the Health Physics Journal, Volume 78 No. 6, June 2000, "EFFECTS OF TIME OF ADMINISTRATION AND DIETARY IODINE LEVELS ON POTASSIUM IODIDE (KI) BLOCKADE OF THYROID IRRADIATION BY 131-I FROM RADIOACTIVE FALLOUT" Pat B. Zanzonico and David V. Becker
(Read abstract by searching title at Health Physics Journal): "KI administered up to 48 hours before 131-I exposure can almost completely block thyroid uptake and therefore greatly reduce the thyroid absorbed dose. However, KI administration 96 hours or more before 131-I exposure has no significant protective effect. In contrast, KI administration after exposure to radioiodine induces a smaller and rapidly decreasing blockade effect. KI administration 16 hours or later.

Updated June 26, 2002