Potassium iodide is an
essential component of any emergency preparedness kit aimed at survival
following a radiological event. By providing stable iodine, potassium
iodide counteracts the effects of radioactive iodine, a common byproduct
of a nuclear attack or accident. The body requires iodine to create
and regulate thyroid hormones.
How Does Potassium Iodide Work?
When the radioactive version of the salt enters the air or poisons food,
the thyroid gland absorbs the harmful chemical, producing internal
contamination. Potassium iodide provides stable iodine that can prevent
the absorption of radioactive iodine even during a radiological or
nuclear event. The thyroid gland becomes so full of stable iodine that
it cannot begin to process additional salt for 24 hours. While table
salt also contains iodine, it does not provide a sufficient enough dose
to block the absorption of radioactive iodine. IOSAT packets provide
potassium iodide in convenient tablets with the necessary concentration
to prevent harm to the thyroid gland.
Is Potassium Iodide Successful?
The success of potassium iodide depends on numerous factors. Because
the chemical does not completely protect an individual against
radioactive iodine exposure, precautions should be taken to increase the
likelihood of success. Potassium iodide taken directly before or after
a nuclear event will provide the best protection. The more time that
passes between exposure and supplementation, the higher the risk of
poisoning. While individuals can increase the odds of survival by
having IOSAT packets or other potassium iodide products in an
easy-to-reach emergency preparedness kit, they cannot control the amount
of radioactive iodine in the air or how quickly the potassium iodide
absorbs in their blood.
Potassium iodide cannot stop radioactive iodine from contaminating the
body. While it buffers the thyroid gland against poisoning, other parts
of the body are still susceptible to injury and harm. Radioactive
iodine is only one of numerous chemicals and particles released into the
air and food following a nuclear event or terrorist attack. While it
definitely helps, individuals should take caution to include other
supplements and medications in their emergency preparedness kits geared
at other health concerns. Finally, once radioactive iodine has damaged
the thyroid gland, potassium iodide cannot reverse the damage.
Is Potassium Iodide Safe?
Following a nuclear attack, the benefits of potassium iodide outweigh
any risks. Common side effects of the medication include rashes,
allergic reactions, stomach aches and salivary gland problems. More
serious consequences can occur when individuals take too high a dose of
potassium iodide, take it too often or suffer from pre-existing thyroid
complications. In infants, hypothyroidism may develop following
potassium iodide supplementation.
Potassium iodide in smaller doses is safe for infants and children.
Pregnant or breast-feeding women should take the drug for protection.
Young adults, while not as susceptible to radioactive iodine, should
take the recommended dose following a nuclear event. Older adults
should refrain from potassium iodide use unless large levels of
contamination are expected. Older adults have a higher likelihood of
allergic reaction and develop less thyroid injuries following
Radiation is any form of energy propagated as rays,
waves or energetic particles that travel through the air or a material
Radioactive materials are composed of atoms that are unstable.
An unstable atom gives off its excess energy until it becomes stable.
The energy emitted is radiation. The process by which an atom changes
from an unstable state to a more stable state by emitting radiation is
called radioactive decay or radioactivity.
People receive some natural
or background radiation exposure each day from the sun, radioactive
elements in the soil and rocks, household appliances (like television
sets and microwave ovens), and medical and dental x-rays. Even the human
body itself emits radiation. These levels of natural and background
radiation is normal. The average American receives 360 millirems of
radiation each year, 300 from natural sources and 60 from man-made
activities. (A rem is a unit of radiation exposure.)
handled improperly--or radiation accidentally released into the
environment, can be dangerous because of the harmful effects of certain
types of radiation on the body. The longer a person is exposed to
radiation and the closer the person is to the radiation, the greater the
Although radiation cannot be detected by the senses (sight,
smell, etc.), it is easily detected by scientists with sophisticated
instruments that can detect even the smallest levels of radiation.
Preparing For An Emergency
Federal, State and local
officials work together to develop site-specific emergency response
plans for nuclear power plant accidents. These plans are tested through
exercises that include protective actions for schools and nursing homes.
plans also delineate evacuation routes, reception centers for those
seeking radiological monitoring and location of congregate care centers
for temporary lodging.
State and local governments, with support from the
Federal government and utilities, develop plans that include a plume
emergency planning zone with a radius of 10 miles from the plant, and an
ingestion planning zone within a radius of 50 miles from the plant.
the 10-mile emergency planning zone are regularly disseminated
emergency information materials (via brochures, the phone book,
calendars, utility bills, etc.). These materials contain educational
information on radiation, instructions for evacuation and sheltering,
special arrangements for the handicapped, contacts for additional
information, etc. Residents should be familiar with these emergency
Radiological emergency plans call for a prompt
Alert and Notification system. If needed, this prompt Alert and
Notification System will be activated quickly to inform the public of
any potential threat from natural or man-made events. This system uses
either sirens, tone alert radios, route alerting (the "Paul Revere"
method), or a combination to notify the public to tune their radios or
television to an Emergency Alert System (EAS) station.
The EAS stations will
provide information and emergency instructions for the public to follow.
If you are alerted, tune to your local EAS station which includes radio
stations, television stations, NOAA weather radio, and the cable TV
Special plans must be made to assist and care for persons who
are medically disabled or handicapped. If you or someone you know lives
within ten miles of a nuclear facility, please notify and register with
your local emergency management agency. Adequate assistance will be
provided during an emergency.
In the most serious case, evacuations
will be recommended based on particular plant conditions rather than
waiting for the situation to deteriorate and an actual release of
radionuclides to occur.
Preparedness for commercial nuclear power plants includes a
system for notifying the public if a problem occurs at a plant. The
emergency classification level of the problem is defined by these four
Notification of Unusual Event
is the least serious of the four levels. The event poses no threat to
you or to plant employees, but emergency officials are notified. No
action by the public is necessary.
is declared when an event has occurred that could reduce the plant's
level of safety, but backup plant systems still work. Emergency agencies
are notified and kept informed, but no action by the public is
Site Area Emergency is
declared when an event involving major problems with the plant's safety
systems has progressed to the point that a release of some radioactivity
into the air or water is possible, but is not expected to exceed
Environmental Protection Agency Protective Action Guidelines (PAGs)
beyond the site boundary. Thus, no action by the public is necessary.
General Emergency is the most serious of
the four classifications and is declared when an event at the plant has
caused a loss of safety systems. If such an event occurs, radiation
could be released that would travel beyond the site boundary. State and
local authorities will take action to protect the residents living near
the plant. The alert and notification system will be sounded. People in
the affected areas could be advised to evacuate promptly or, in some
situations, to shelter in place. When the sirens are sounded, you should
listen to your radio, television and tone alert radios for
site-specific information and instructions.
You Are Alerted
- Remember that
siren or tone alert radio does not mean
should evacuate. It means you should
turn to an EAS station to determine
is only a test or an actual emergency.
- Tune to your local radio or television station
for information. The warning siren could mean a nuclear power plant
emergency or the sirens could be used as a warning for tornado, fire,
flood, chemical spill, etc.
- Check on your neighbors.
- Do not call 911. Special rumor control numbers
and information will be provided to the public for a nuclear power
plant emergency, either during the EAS message, in the utilities' public
information brochure, or both.
- In a nuclear
power plant emergency, you may be advised to go indoors and, if so, to
close all windows, doors, chimney dampers, other sources of outside air,
and turn off forced air heating and cooling equipment, etc.
You Are Advised to Evacuate the Area
- Stay calm and
do not rush
- Listen to emergency
- Close and lock windows and
- Turn off air conditioning, vents, fans, and
- Close fire place dampers
Take a few
items with you. Gather personal items you or your family might need:
- Flash light and extra batteries
battery operated radio and extra batteries
- First aid kit
- Emergency food and water
- Cash and credit cards
Use your own
transportation or make arrangements to ride with a neighbor. Public
transportation should be available for those who have not made
arrangements. Keep car windows and air vents closed and listen to an EAS
Follow the evacuation routes provided. If you need a
place to stay, congregate care information will be provided.
If Advised to remain at Home
- Close and lock windows and
- Turn off air conditioning, vents, fans and
- Close fireplace dampers
to the basement or other underground area
- Stay inside
until authorities say it is safe
Coming In From Outdoors
- Shower and
change clothing and shoes
- Put items
worn outdoors in a plastic bag and seal it.
thyroid gland is vulnerable to the intake of radioactive iodine
(radioactive fallout/dust). If a radiological release occurs at a
nuclear power plant, States may decide to provide the public with a
stable iodine, potassium
iodide, which saturates the thyroid and
protects it (99%) from the effects of radioactive iodine (thyroid
cancer) if taken in time. Such a protective action is at the option of
State, and in some cases, local government or power plant.
If an incident
involving an actual or potential radiological release occurs,
consideration is given to the safety of the children. If an emergency is
declared, students in the 10-mile emergency planning zone will be
relocated to designated facilities in a safe area. Usually, as a
precautionary measure, school children are relocated prior to the
evacuation of the general public.
Farmers and Home Gardeners
If a radiological incident occurs at the
nuclear facility, periodic information concerning the safety of farm
and home grown products will be provided. Information on actions you can
take to protect crops and livestock is available from your agricultural
Normal harvesting and
processing may still be possible if time permits. Unharvested crops are
hard to protect.
Crops already harvested should be stored inside if
Wash and peel vegetables and fruits before use if they were not
Provide as much shelter as
possible. Take care of milk-producing animals.
Provide plenty of food and
water and make sure shelters are well-ventilated. Use stored feed and
water, when possible.
Three Ways to
Minimize Radiation Exposure
There are three factors
that minimize radiation exposure to your body: Time, Distance, and
loses its strength fairly quickly. Limiting the time spent near the
source of radiation reduces the amount of radiation exposure you will
receive. Following an accident, local authorities will monitor any
release of radiation and determine the level of protective actions and
when the threat has passed.
more distance between you and the source of the radiation, the less
radiation you will receive. In the most serious nuclear power plant
accident, local officials will likely call for an evacuation, thereby
increasing the distance between you and the radiation.
distance, the more heavy, dense materials between you and the source of
the radiation, the better. This is why local officials could advise you
to remain indoors if an accident occurs. In some cases, the walls in
your home or workplace would be sufficient shielding to protect you for a
short period of time.
What you can do to stay
Attend public information meetings. You may also want to attend
post-exercise meetings that include the media and the public.
emergency management officials, who can provide information about
radioactivity, safety precautions, and state, local, industry and
Ask about the hazards radiation may pose to your family,
especially with respect to young children, pregnant women and the
Ask where nuclear power plants are located.
Learn your community's
Learn emergency plans for schools, day care
centers, nursing homes--anywhere family members might be.
Be familiar with emergency information materials that are
regularly disseminated to your home (via brochures, the phone book,
calendars, utility bills, etc.) These materials contain educational
information on radiation, instructions for evacuation and sheltering,
special arrangements for the handicapped, contacts for additional
information, etc. Home Preparation Procedure for Emergency Administration of
Potassium Iodide Tablets to Infants and Small Children
In the event of accidental release (or
nuclear explosion, terrorist nuclear weapon) of radioactive iodine into
the atmosphere, potassium iodide (KI) is recommended for use as an aid
to other emergency measures, such as evacuation and food control
measures. When used correctly, potassium iodide can prevent or reduce
the amount of radioactive iodine taken up by the thyroid gland. The
government stockpiles potassium iodide for emergency uses, such as in
the event of an unexpected release of radioactive iodide.
Potassium iodide (KI) is stockpiled as
tablets because tablets are easier to store; however, infants and small
children cannot swallow tablets. In an emergency such as an unexpected
release of radioactive iodine, the potassium iodide tablets may
need to be given to infants and children by their parents or caregivers.
Since potassium iodide dissolved in water may be too salty to
drink, the Food and Drug Administration (FDA) is providing parents or
caregivers with instructions on how to mix the potassium iodide tablets
with a food or a drink to disguise the taste so infants and small
children will take the medicine in an emergency. To see what worked
best to disguise the taste of potassium iodide, FDA asked adults to
taste the following six mixtures of potassium iodide and drinks.
- Low fat white milk
- Low fat chocolate milk
- Orange juice
- Flat Soda (For example, cola)
- Raspberry syrup
The mixture of potassium iodide with
raspberry syrup disguises the taste of potassium iodide best.
The mixtures of potassium iodide with low fat chocolate milk, orange
juice, and flat soda (for example, cola) generally have an acceptable
taste. Low fat white milk and water did not hide the salty taste of
INGREDIENTS AND SUPPLIES NEEDED TO
PREPARE POTASSIUM IODIDE (KI) TABLETS
- Potassium iodide (KI) 130
- Metal teaspoon
- Small bowl
- One of the drinks from the list
above or infant formula.
PREPARATION FOR 130 MG
POTASSIUM IODIDE TABLET
1. Grinding the potassium iodide
tablet into powder
- Put one 130mg potassium iodide tablet into a small
bowl and grind it into a fine powder using the back of the metal
teaspoon against the inside of the bowl. The powder should not have any
2. Mixing potassium iodide powder into a drink
- Add four teaspoonfuls of water to the potassium iodide
powder in the small bowl. Use a spoon to mix them together until the
potassium iodide powder is dissolved in the water.
3. Mix drink of choice with potassium iodide powder and water
- Add four teaspoonfuls of drink to the potassium iodide
powder and water mixture described in Step 2.
The amount of potassium iodide in the drink is 16.25 mg per teaspoon.
The number of teaspoonfuls of the drink to give your child depends on
your child's age. There is a chart at the end of these directions to
tell you how much to give your child.
The potassium iodide in any of the six
drinks listed above and infant formulas will keep for up to seven days
in the refrigerator. FDA recommends that the
potassium iodide drink mixtures be prepared weekly; unused portions
should be discarded.
FDA recommends doses for
potassium iodide based on age, predicted thyroid exposure to
radioiodines, and for women -- whether the woman is pregnant or nursing
(see Table 1). Adults over 18 years of age and pregnant or lactating
women should take the potassium iodide 130 mg tablet. Infants,
children, and adolescents through 18 years of age should take potassium
iodide in a drink prepared according to the procedure described above.
Table 2 shows how many teaspoonfuls of potassium iodide mixture to give
to an adolescent, child, or infant. The dose of potassium iodide
should be taken once a day until a risk of significant exposure to
radioiodines no longer exists.
Table 1. Threshold thyroid radioactivity
exposures and the recommended dose of Potassium iodide (KI) for
If you are:
And your predicted
Thyroid Exposure is
Then you should take:
130 mg tablets
An adult over the age of 40
Equal to or greater than 500 centi-grays (cGy)
a 130 mg dose of
potassium Iodide (KI)
An adult between the ages of
18 and 40
Equal to or greater than 10 cGy
A pregnant or lactating woman
Equal to or greater than 5cGy
1 FDA, Guidance:
Potassium Iodide as a Thyroid Blocking Agent in Radiation Emergencies,
Table 2. Recommended doses of KI for
adolescents, children, and infants with predicted thyroid radioactivity
exposures equal to or greater than 5 cGy1, using 130 mg
If your child is:
Give your child this
amount of Potassium Iodide (KI) *
An adolescent between 12 and 18 years
65 mg of potassium iodide (KI)
Between 4 and 12 years old
65 mg of potassium iodide (KI)
Over 1 month through 3 years
32.5 mg of potassium iodide (KI)
An infant from birth through 1 month
(NOT a tablespoonful)
16.25 mg of potassium iodide (KI)
* This is the amount to give your
child for one dose. You should give your child one dose each day.
** Adolescents approaching adult size
[equal to or greater than 154 pounds (70 kg)] should receive the full
adult dose (130 mg tablet or 8 teaspoonfuls of KI mixture).
1 FDA, Guidance: Potassium
Iodide as a Thyroid Blocking Agent in Radiation Emergencies, December
2001.original table below
How Does Potassium Iodide Provide Anti-Radiation Protection?
- "The thyroid gland is especially vulnerable to atomic injury since radioactive isotopes of iodine are a major component of fallout." New England Journal of Medicine. Vol. 274 on Page 1442
- "There is no medicine that will effectively prevent nuclear radiations from damaging the human body cells that they strike.However, a salt of the elements potassium and iodine, taken orally even in very small quantities 1/2 hour to 1 day before radioactive iodines are swallowed or inhaled, prevents about 99% of the damage to the thyroid gland that otherwise would result. The thyroid gland readily absorbs both non-radioactive and radioactive iodine, and normally it retains much of this element in either or both forms.
When ordinary, non-radioactive iodine is made available in the blood for absorption by the thyroid gland before any radioactive iodine is made available, the gland will absorb and retain so much that it becomes saturated with non-radioactive iodine. When saturated, the thyroid can absorb only about l% as much additional iodine, including radioactive forms that later may become available in the blood: then it is said to be blocked. (Excess iodine in the blood is rapidly eliminated by the action of the kidneys.) page 111 Nuclear War Survival Skills, Original Edition,Cresson H. Kearny. Published September, 1979, by Oak Ridge National Laboratory, a Facility of the U.S. Department of Energy (Updated and Expanded 1987 Edition)
- "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." The Nuclear Regulatory Commission (NRC. July 1, 1998 in USE OF POTASSIUM IODIDE IN EMERGENCY RESPONSE
- "Stable iodine administered before, or promptly after, intake of radioactive iodine can block or reduce the accumulation of radioactive iodine in the thyroid."World Health Organization (WHO) Guidelines for Iodine Prophylaxis following Nuclear Accidents. Updated 1999.
"The effectiveness of KI as a specific blocker of thyroid radioiodine uptake is well established (Il'in LA, et al., 1972) as are the doses necessary for blocking uptake. As such, it is reasonable to conclude that KI will likewise be effective in reducing the risk of thyroid cancer in individuals or populations at risk for inhalation or ingestion of radioiodines."
"Thus, the studies following the Chernobyl accident support the etiologic role of relatively small doses of radioiodine in the dramatic increase in thyroid cancer among exposed children. Furthermore, it appears that the increased risk occurs with a relatively short latency. Finally, the Polish experience supports the use of KI as a safe and effective means by which to protect against thyroid cancer caused by internal thyroid irradiation from inhalation of contaminated air or ingestion of contaminated food and drink when exposure cannot be prevented by evacuation, sheltering, or food and milk control." FDA
Dosage and Safety Regarding Potassium Iodide (KI) Usage
"Based on the FDA adverse reaction reports and an estimated 48 x 106 [48 million] 300-mg doses of potassium iodide administered each year [in the United States], the NCRP [National Council on Radiation Protection and Measurements] estimated an adverse reaction rate of from 1 in a million to 1 in 10 million doses." (It should be pointed out that this extremely low adverse reaction rate is for doses over twice as large as the 130-mg prophylactic dose.)
U.S. Department of Health and Human Services Food and Drug Administration
Potassium Iodide as a Thyroid Blocking Agent in Radiation Emergencies
U.S. Department of Health and Human Services
Food and Drug Administration
Center for Drug Evaluation and Research (CDER)
Additional copies are available from:
Office of Training and Communications
Division of Communications Management
Drug Information Branch, HFD-210
5600 Fishers Lane
Rockville, MD 20857
Potassium Iodide as a Thyroid Blocking
Agent in Radiation Emergencies
This guidance represents the Food and Drug Administration's (FDA's) current thinking on this topic. It does not create or confer any rights for or on any person and does not operate to bind FDA or the public. An alternative approach may be used if such approach satisfies the requirements of the applicable statutes and regulations.
The objective of this document is to provide guidance to other Federal agencies, including the Environmental Protection Agency (EPA) and the Nuclear Regulatory Commission (NRC), and to state and local governments regarding the safe and effective use of potassium iodide (KI) as an adjunct to other public health protective measures in the event that radioactive iodine is released into the environment. The adoption and implementation of these recommendations are at the discretion of the state and local governments responsible for developing regional emergency-response plans related to radiation emergencies.
This guidance updates the Food and Drug Administration (FDA) 1982 recommendations for the use of KI to reduce the risk of thyroid cancer in radiation emergencies involving the release of radioactive iodine. The recommendations in this guidance address KI dosage and the projected radiation exposure at which the drug should be used.
These recommendations were prepared by the Potassium Iodide Working Group, comprising scientists from the FDA's Center for Drug Evaluation and Research (CDER) and Center for Devices and Radiological Health (CDRH) in collaboration with experts in the field from the National Institutes of Health (NIH). Although they differ in two respects (as discussed in Section IV.B), these revised recommendations are in general accordance with those of the World Health Organization (WHO), as expressed in its Guidelines for Iodine Prophylaxis Following Nuclear Accidents: Update 1999 (WHO 1999).
Under 44 CFR 351, the Federal Emergency Management Agency (FEMA) has established roles and responsibilities for Federal agencies in assisting state and local governments in their radiological emergency planning and preparedness activities. The Federal agencies, including the Department of Health and Human Services (HHS), are to carry out these roles and responsibilities as members of the Federal Radiological Preparedness Coordinating Committee (FRPCC). Under 44 CFR 351.23(f), HHS is directed to provide guidance to state and local governments on the use of radioprotective substances and the prophylactic use of drugs (e.g., KI) to reduce the radiation dose to specific organs. This guidance includes information about dosage and projected radiation exposures at which such drugs should be used.
The FDA has provided guidance previously on the use of KI as a thyroid blocking agent. In the Federal Register of December 15, 1978, FDA announced its conclusion that KI is a safe and effective means by which to block uptake of radioiodines by the thyroid gland in a radiation emergency under certain specified conditions of use. In the Federal Register of June 29, 1982, FDA announced final recommendations on the administration of KI to the general public in a radiation emergency. Those recommendations were formulated after reviewing studies relating radiation dose to thyroid disease risk that relied on estimates of external thyroid irradiation after the nuclear detonations at Hiroshima and Nagasaki and analogous studies among children who received therapeutic radiation to the head and neck. Those recommendations concluded that at a projected dose to the thyroid gland of 25 cGy or greater from ingested or inhaledradioiodines, the risks of short-term use of small quantities of KI were outweighed by the benefits of suppressingradioiodine-induced thyroid cancer.1 The amount of KI recommended at that time was 130 mg per day for adults and children above 1 year of age and 65 mg per day for children below 1 year of age. The guidance that follows revises our 1982 recommendations on the use of KI for thyroid cancer prophylaxis based on a comprehensive review of the data relating radioioidine exposure to thyroid cancer risk accumulated in the aftermath of the 1986 Chernobyl reactor accident.
III. DATA SOURCES
A. Reliance on Data from Chernobyl
In epidemiological studies investigating the relationship between thyroidal radioiodine exposure and risk of thyroid cancer, the estimation of thyroid radiation doses is a critical and complex aspect of the analyses. Estimates of exposure, both for individuals and across populations, have been reached in different studies by the variable combination of (1) direct thyroid measurements in a segment of the exposed population; (2) measurements of 131I (iodine isotope) concentrations in the milk consumed by different groups (e.g., communities) and of the quantity of milk consumed; (3) inference from ground deposition of long-lived radioisotopes released coincidentally and presumably in fixed ratios with radioiodines; and (4) reconstruction of the nature and extent of the actual radiation release.
All estimates of individual and population exposure contain some degree of uncertainty. The uncertainty is least for estimates of individual exposure based on direct thyroid measurements. Uncertainty increases with reliance on milk consumption estimates; is still greater with estimates derived from ground deposition of long-lived radioisotopes, and is highest for estimates that rely heavily on release reconstruction.
Direct measurements of thyroid radioactivity are unavailable from the Hanford, Nevada Test Site, and Marshall Islands exposures. Indeed, the estimates of thyroid radiation doses related to these releases rely heavily on release reconstructions and, in the former two cases, on recall of the extent of milk consumption 40 to 50 years after the fact. In the Marshall Islands cohort, urinary radioiodine excretion data were obtained and used in calculating exposure estimates.
Because of the great uncertainty in the dose estimates from the Hanford and Nevada Test Site exposures and due to the small numbers of thyroid cancers occurring in the populations potentially exposed, the epidemiological studies of the excess thyroid cancer risk related to these radioiodine releases are, at best, inconclusive. As explained below, the dosimetric data derived in the studies of individual and population exposures following the Chernobyl accident, although not perfect, are unquestionably superior to data from previous releases. In addition, the results of the earlier studies are inadequate to refute cogent case control study evidence from Chernobyl of a cause-effect relationship between thyroid radioiodine deposition and thyroid cancer risk.2
The Chernobyl reactor accident of April 1986 provides the best-documented example of a massive radionuclide release in which large numbers of people across a broad geographical area were exposed acutely to radioiodines released into the atmosphere. Therefore, the recommendations contained in this guidance are derived from our review of the Chernobyl data as they pertain to the large number of thyroid cancers that occurred. These are the most comprehensive and reliable data available describing the relationship between thyroid radiation dose and risk for thyroid cancer following an environmental release of 131I. In contrast, the exposures resulting from radiation releases at the Hanford Site in Washington State in the mid-1940s and in association with the nuclear detonations at the Nevada Test Site in the 1950s were extended over years, rather than days to weeks, contributing to the difficulty in estimating radioactive dose in those potentially exposed (Davis et al., 1999; Gilbert et al., 1998). The exposure of Marshall Islanders to fallout from the nuclear detonation on Bikini in 1954 involved relatively few people, and although the high rate of subsequent thyroid nodules and cancers in the exposed population was likely caused in large part by radioiodines, the Marshall Islands data provide little insight into the dose-response relationship between radioactive iodine exposure and thyroid cancer risk (Robbins and Adams 1989).
Beginning within a week after the Chernobyl accident, direct measurements of thyroid exposure were made in hundreds of thousands of individuals, across three republics of the former Soviet Union (Robbins and Schneider 2000, Gavrilin et al., 1999, Likhtarev et al., 1993, Zvonova and Balonov 1993). These thyroid measurements were used to derive, in a direct manner, the thyroid doses received by the individuals from whom the measurements were taken. The thyroid measurements were also used as a guide to estimate the thyroid doses received by other people, taking into account differences in age, milk consumption rates, and ground deposition densities, among other things. The thyroid doses derived from thyroid measurements have a large degree of uncertainty, especially in Belarus, where most of the measurements were made by inexperienced people with detectors that were not ideally suited to the task at hand (Gavrilin et al., 1999 and UNSCEAR 2000). However, as indicated above, the uncertainties attached to thyroid dose estimates derived from thyroid measurements are, as a rule, lower than those obtained without recourse to those measurements.
It is also notable that the thyroid radiation exposures after Chernobyl were virtually all internal, from radioiodines. Despite some degree of uncertainty in the doses received, it is reasonable to conclude that the contribution of external radiation was negligible for most individuals. This distinguishes the Chernobyl exposures from those of the Marshall Islanders. Thus, the increase in thyroid cancer seen after Chernobyl is attributable to ingested or inhaled radioiodines. A comparable burden of excess thyroid cancers could conceivably accrue should U.S. populations be similarly exposed in the event of a nuclear accident. This potential hazard highlights the value of averting such risk by using KI as an adjunct to evacuation, sheltering, and control of contaminated foodstuffs.
The Chernobyl reactor accident resulted in massive releases of 131I and other radioiodines. Beginning approximately 4 years after the accident, a sharp increase in the incidence of thyroid cancer among children and adolescents in Belarus and Ukraine (areas covered by the radioactive plume) was observed. In some regions, for the first 4 years of this striking increase, observed cases of thyroid cancer among children aged 0 through 4 years at the time of the accident exceeded expected number of cases by 30- to 60-fold. During the ensuing years, in the most heavily affected areas, incidence is as much as 100-fold compared to pre-Chernobyl rates (Robbins and Schneider 2000; Gavrilin et al., 1999; Likhtarev et al., 1993; Zvonova and Balonov 1993). The majority of cases occurred in children who apparently received less than 30 cGy to the thyroid (Astakhova et al., 1998). A few cases occurred in children exposed to estimated doses of < 1 cGy; however, the uncertainty of these estimates confounded by medical radiation exposures leaves doubt as to the causal role of these doses of radioiodine (Souchkevitch and Tsyb 1996).
The evidence, though indirect, that the increased incidence of thyroid cancer observed among persons exposed during childhood in the most heavily contaminated regions in Belarus, Ukraine, and the Russian Federation is related to exposure to iodine isotopes is, nevertheless, very strong (IARC 2001). We have concluded that the best dose-response information from Chernobyl shows a marked increase in risk of thyroid cancer in children with exposures of 5 cGy or greater (Astakhova et. al., 1998; Ivanov et al., 1999; Kazakov et al., 1992). Among children born more than nine months after the accident in areas traversed by the radioactive plume, the incidence of thyroid cancer has not exceeded preaccident rates, consistent with the short half-life of 131I.
The use of KI in Poland after the Chernobyl accident provides us with useful information regarding its safety and tolerability in the general population. Approximately 10.5 million children under age 16 and 7 million adults received at least one dose of KI. Of note, among newborns receiving single doses of 15 mg KI, 0.37 percent (12 of 3214) showed transient increases in TSH (thyroid stimulating hormone) and decreases in FT4 (free thyroxine). The side effects among adults and children were generally mild and not clinically significant. Side effects included gastrointestinal distress, which was reported more frequently in children (up to 2 percent, felt to be due to bad taste of SSKI solution) and rash (~1 percent in children and adults). Two allergic reactions were observed in adults with known iodine sensitivity (Nauman and Wolff 1993).
Thus, the studies following the Chernobyl accident support the etiologic role of relatively small doses of radioiodine in the dramatic increase in thyroid cancer among exposed children. Furthermore, it appears that the increased risk occurs with a relatively short latency. Finally, the Polish experience supports the use of KI as a safe and effective means by which to protect against thyroid cancer caused by internal thyroid irradiation from inhalation of contaminated air or ingestion of contaminated food and drink when exposure cannot be prevented by evacuation, sheltering, or food and milk control.
IV.CONCLUSIONS AND RECOMMENDATIONS
A. Use of KI in Radiation Emergencies: Rationale, Effectiveness, Safety
For the reasons discussed above, the Chernobyl data provide the most reliable information available to date on the relationship between internal thyroid radioactive dose and cancer risk. They suggest that the risk of thyroid cancer is inversely related to age, and that, especially in young children, it may accrue at very low levels of radioiodine exposure. We have relied on the Chernobyl data to formulate our specific recommendations below.
The effectiveness of KI as a specific blocker of thyroid radioiodine uptake is well established (Il'in LA, et al., 1972) as are the doses necessary for blocking uptake. As such, it is reasonable to conclude that KI will likewise be effective in reducing the risk of thyroid cancer in individuals or populations at risk for inhalation or ingestion of radioiodines.
Short-term administration of KI at thyroid blocking doses is safe and, in general, more so in children than adults. The risks of stable iodine administration include sialadenitis (an inflammation of the salivary gland, of which no cases were reported in Poland among users after the Chernobyl accident), gastrointestinal disturbances, allergic reactions and minor rashes. In addition, persons with known iodine sensitivity should avoid KI, as should individuals with dermatitis herpetiformis and hypocomplementemic vasculitis, extremely rare conditions associated with an increased risk of iodine hypersensitivity.
Thyroidal side effects of stable iodine include iodine-induced thyrotoxicosis, which is more common in older people and in iodine deficient areas but usually requires repeated doses of stable iodine. In addition, iodide goiter and hypothyroidism are potential side effects more common in iodine sufficient areas, but they require chronic high doses of stable iodine (Rubery 1990). In light of the preceding, individuals with multinodular goiter, Graves' disease, and autoimmune thyroiditis should be treated with caution, especially if dosing extends beyond a few days. The vast majority of such individuals will be adults.
The transient hypothyroidism observed in 0.37 percent (12 of 3214) of neonates treated with KI in Poland after Chernobyl has been without reported sequelae to date. There is no question that the benefits of KI treatment to reduce the risk of thyroid cancer outweigh the risks of such treatment in neonates. Nevertheless, in light of the potential consequences of even transient hypothyroidism for intellectual development, we recommend that neonates (within the first month of life) treated with KI be monitored for this effect by measurement of TSH (and FT4, if indicated) and that thyroid hormone therapy be instituted in cases in which hypothyroidism develops (Bongers-Schokking 2000; Fisher 2000; Calaciura 1995).
B.KI Use in Radiation Emergencies: Treatment Recommendations
After careful review of the data from Chernobyl relating estimated thyroid radiation dose and cancer risk in exposed children, FDA is revising its recommendation for administration of KI based on age, predicted thyroid exposure, and pregnancy and lactation status (see Table).
Threshold Thyroid Radioactive Exposures and
Recommended Doses of KI for Different Risk Groups
KI dose (mg)
# of 130 mg tablets
# of 65
Adults over 40 yrs
Adults over 18 through 40 yrs
Pregnant or lactating women
Adoles. over 12 through 18 yrs*
Children over 3 through 12 yrs
Over 1 month through 3 years
Birth through 1 month
*Adolescents approaching adult size (> 70 kg) should receive the full adult dose (130 mg).
The protective effect of KI lasts approximately 24 hours. For optimal prophylaxis, KI should therefore be dosed daily, until a risk of significant exposure to radioiodines by either inhalation or ingestion no longer exists. Individuals intolerant of KI at protective doses, and neonates, pregnant and lactating women (in whom repeat administration of KI 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 KI 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 KI 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 KI 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 KI far exceed the risks of overdosing, especially in children, though we continue to emphasize particular attention to dose in infants.
These FDA recommendations differ from those put forward in the World Health Organization (WHO) 1999 guidelines for iodine prophylaxis in two ways. WHO recommends a 130-mg dose of KI for adults and adolescents (over 12 years). For the sake of logistical simplicity in the dispensing and administration of KI to children, FDA recommends a 65-mg dose as standard for all school-age children while allowing for the adult dose (130 mg, 2 X 65 mg tablets) in adolescents approaching adult size. The other difference lies in the threshold for predicted exposure of those up to 18 years of age and of pregnant or lactating women that should trigger KI prophylaxis. WHO recommends a threshold of 1 cGy for these two groups. As stated earlier, FDA has concluded from the Chernobyl data that the most reliable evidence supports a significant increase in the risk of childhood thyroid cancer at exposures of 5 cGy or greater.
The downward KI dose adjustment by age group, based on body size considerations, adheres to the principle of minimum effective dose. The recommended standard dose of KI for all school-age children is the same (65 mg). However, adolescents approaching adult size (i.e., >70 kg) should receive the full adult dose (130 mg) for maximal block of thyroid radioiodine uptake. Neonates ideally should receive the lowest dose (16 mg) of KI. Repeat dosing of KI should be avoided in the neonate to minimize the risk of hypothyroidism during that critical phase of brain development (Bongers-Schokking 2000; Calaciura et al., 1995). KI from tablets (either whole or fractions) or as fresh saturated KI solution may be diluted in milk, formula, or water and the appropriate volume administered to babies. As stated above, we recommend that neonates (within the first month of life) treated with KI be monitored for the potential development of hypothyroidism by measurement of TSH (and FT4, if indicated) and that thyroid hormone therapy be instituted in cases in which hypothyroidism develops (Bongers-Schokking 2000; Fisher 2000; Calaciura et al., 1995).
Pregnant women should be given KI for their own protection and for that of the fetus, as iodine (whether stable or radioactive) readily crosses the placenta. However, because of the risk of blocking fetal thyroid function with excess stable iodine, repeat dosing with KI of pregnant women should be avoided. Lactating females should be administered KI for their own protection, as for other young adults, and potentially to reduce the radioiodine content of the breast milk, but not as a means to deliver KI to infants, who should get their KI directly. As for direct administration of KI, stable iodine as a component of breast milk may also pose a risk of hypothyroidism in nursing neonates. Therefore, repeat dosing with KI should be avoided in the lactating mother, except during continuing severe contamination. If repeat dosing of the mother is necessary, the nursing neonate should be monitored as recommended above.
V. ADDITIONAL CONSIDERATIONS IN PROPHYLAXIS AGAINST THYROID RADIOIODINE EXPOSURE
Certain principles should guide emergency planning and implementation of KI prophylaxis in the event of a radiation emergency. After the Chernobyl accident, across the affected populations, thyroid radiation exposures occurred largely due to consumption of contaminated fresh cow's milk (this contamination was the result of milk cows grazing on fields affected by radioactive fallout) and to a much lesser extent by consumption of contaminated vegetables. In this or similar accidents, for those residing in the immediate area of the accident or otherwise directly exposed to the radioactive plume, inhalation of radioiodines may be a significant contributor to individual and population exposures. As a practical matter, it may not be possible to assess the risk of thyroid exposure from inhaled radioiodines at the time of the emergency. The risk depends on factors such as the magnitude and rate of the radioiodine release, wind direction and other atmospheric conditions, and thus may affect people both near to and far from the accident site.
For optimal protection against inhaled radioiodines, KI should be administered before or immediately coincident with passage of the radioactive cloud, though KI may still have a
substantial protective effect even if taken 3 or 4 hours after exposure. Furthermore, if the release of radioiodines into the atmosphere is protracted, then, of course, even delayed administration may reap benefits by reducing, if incompletely, the total radiation dose to the thyroid.
Prevention of thyroid uptake of ingested radioiodines, once the plume has passed and radiation protection measures (including KI) are in place, is best accomplished by food control measures and not by repeated administration of KI. Because of radioactive decay, grain products and canned milk or vegetables from sources affected by radioactive fallout, if stored for weeks to months after production, pose no radiation risk. Thus, late KI prophylaxis at the time of consumption is not required.
As time is of the essence in optimal prophylaxis with KI, timely administration to the public is a critical consideration in planning the emergency response to a radiation accident and requires a ready supply of KI. State and local governments choosing to incorporate KI into their emergency response plans may consider the option of predistribution of KI to those individuals who do not have a medical condition precluding its use.
FDA maintains that KI is a safe and effective means by which to prevent radioiodine uptake by the thyroid gland, under certain specified conditions of use, and thereby obviate the risk of thyroid cancer in the event of a radiation emergency. Based upon review of the literature, we have proposed lower radioactive exposure thresholds for KI prophylaxis as well as lower doses of KI for neonates, infants, and children than we recommended in 1982. As in our 1982 notice in the Federal Register, FDA continues to recommend that radiation emergency response plans include provisions, in the event of a radiation emergency, for informing the public about the magnitude of the radiation hazard, about the manner of use of KI and its potential benefits and risks, and for medical contact, reporting, and assistance systems. FDA also emphasizes that emergency response plans and any systems for ensuring availability of KI to the public should recognize the critical importance of KI administration in advance of exposure to radioiodine. As in the past, FDA continues to work in an ongoing fashion with manufacturers of KI to ensure that high-quality, safe, and effective KI products are available for purchase by consumers as well as by state and local governments wishing to establish stores for emergency distribution.
KI provides protection only for the thyroid from radioiodines. It has no impact on the uptake by the body of other radioactive materials and provides no protection against external irradiation of any kind. FDA emphasizes that the use of KI should be as an adjunct to evacuation (itself not always feasible), sheltering, and control of foodstuffs.
The KI Taskforce would like to extend special thanks to our members from the NIH: Jacob Robbins, M.D., and Jan Wolff, Ph.D., M.D., of the National Institute of Diabetes, Digestive, and Kidney Diseases and Andre Bouville, Ph.D., of the National Cancer Institute. In addition, we would like to thank Dr. David V. Becker of the Department of Radiology, Weill Medical College (WMC) of Cornell University and The New York Presbyterian Hospital-WMC Cornell Campus, for his valuable comments on the draft
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1 For the radiation emitted by 131 I (electrons and photons), the radiation-weighting factor is equal to one, so that the absorbed dose to the thyroid gland expressed in centigrays (cGy) is numerically equal to the thyroid equivalent dose expressed in rem (1 cGy = 1 rem).
2 We have included in this guidance an extensive bibliography of the sources used in developing these revised recommendations.
|"The FDA recommends potassium iodide (KI) ... for thyroid blocking in radiation emergencies. ... KI can be used to provide safe and effective protection against thyroid cancer caused by irradiation ... The known potential for potassium iodide to cause serious side effects in a small sensitive population is not sufficient grounds from which to continue to conclude, or even suggest, a significant and quantifiable proportion of serious reactions."|
[Federal Register, December 15, 1978; FDA: "Potassium Iodide as a Thyroid Blocking Agent in Radiation Emergencies", December, 2000.]
|"Radioiodines are the primary internal radiation hazard during the first few weeks after atomic bomb fallout ... [E]ffects from other radioactive materials are considered relatively minor..."|
[NCRP: Reports 42 and 55, New York Times, June 13, 2002.]
|"It is essential that, one way or another, KI be available to protect the public, especially children, in the event of a nuclear accident or act of nuclear terrorism...[T]he United States, virtually alone among developed nations, has failed to apply the principal lesson learned from Chernobyl."|
[ATA: Statement of November 7, 2001]
|"KI can be 100% effective in preventing radiation-induced effects, including thyroid cancer...[I]t should be kept in homes, schools, and day care centers...[Those] at risk should receive KI before exposure, if possible, or immediately afterward."|
[American Academy of Pediatrics, News Release, May 19, 2003; Pediatrics, 2003]
|"Potassium iodide pills should be available to everyone age 40 or younger...living near a nuclear power plant...Federal agencies should keep a backup supply and be prepared to distribute it to affected areas in the event of a nuclear incident... The US government should... help states implement plans for distributing potassium iodide."|
[US National Academy of Sciences: Distribution of Potassium Iodide in the event of a Nuclear Accident; National Research Council, 2004]
|"Excess thyroid cancer in children...from Chernobyl has been established... The increase has been documented up to 500km from the accident site...the Chernobyl accident has demonstrated that significant doses from radioactive iodine can occur hundreds of kilometers beyond (ten-mile) emergency planning zones... [Cancer risk] can be reduced or prevented by implementation of iodine prophylaxis."|
[WHO: Guidelines for Iodine Prophylaxis Following Nuclear Accidents; Update 1999. Geneva]
The following was created
by FEMA (Federal Emergency Management Agency) to inform the public about
preparing for the possibility of a Nuclear Power Plant Emergency.
Nuclear Power Plant
Since 1980, each utility that owns a commercial nuclear power
plant in the United States has been required to have both an onsite and
offsite emergency response plan as a condition of obtaining and
maintaining a license to operate that plant. Onsite emergency response
plans are approved by the Nuclear Regulatory Commission (NRC). Offsite
plans (which are closely coordinated with the utility's onsite emergency
response plan) are evaluated by the Federal Emergency Management Agency
(FEMA) and provided to the NRC, who must consider the FEMA findings
when issuing or maintaining a license.
Federal law establishes the
criterion for determining the adequacy of offsite planning and
preparedness, i.e: "Plans and preparedness must be determined to
adequately protect the public health and safety by providing reasonable
assurance that appropriate measures can be taken offsite in the event of
a radiological emergency."
Although construction and operation of
nuclear power plants are closely monitored and regulated by the NRC, an
accident, though unlikely, is possible. The potential danger from an
accident at a nuclear power plant is exposure to radiation. This
exposure could come from the release of radioactive material from the
plant into the environment, usually characterized by a plume
(cloud-like) formation. The area the radioactive release may affect is
determined by the amount released from the plant, wind direction and
speed and weather conditions (i.e., rain, snow, etc.) which would
quickly drive the radioactive material to the ground, hence causing
increased deposition of radionuclides.
If a release of radiation
occurs, the levels of radioactivity will be monitored by authorities
from Federal and State governments, and the utility, to determine the
potential danger in order to protect the public.