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Potassium Iodide (KI)



Key Information about I-131


  • Sources of I-131:
    • I-131 releases have occurred most frequently after incidents involving nuclear reactors (e.g., Chernobyl, Japan).
    • Nuclear bomb detonation produces a small amount of local I-131 fallout. Most I-131 distributes over large distances, typically with only 10% making its way to the earth's surface before undergoing spontaneous radioactive decay to stable xenon-131.
    • Radioactive iodine is difficult to obtain in quantity and is not considered a likely isotope for use in a Radiological Dispersal Device (RDD).
    • Untoward releases of I-131 requiring medical management are rare.
  • Routes of contamination:
    • After an I-131 release, the amount of the radioisotope available to contaminate the public depends on
      • Amount of I-131 released
      • Distance between a given individual and the place of release
      • Vertical height of the release
      • Meteorological conditions at and after the time of the release
    • Contamination with I-131 begins immediately for persons within the plume in the immediate vicinity of a nuclear release (e.g. from a nuclear power plant).
    • External contamination may occur when a person is caught in the plume or passes through an area left contaminated by fallout from the plume.
    • Inhalation: represents one route of internal contamination of public health significance.
    • Ingestion: Where I-131 is not inhaled, ingestion may represent a more significant route of internal contamination. Doses to humans from inhalation or from ingestion of plants, animals, or water, however, are usually small in comparison to that from milk intake (see below).
    • Historically, milk consumption has been a more significant route of internal contamination than inhalation, both in terms of numbers of individuals affected and internal dose. (Illustration) Deposition of I-131 on pasture grasses, followed by I-131 ingestion by cows or goats and then human ingestion of contaminated milk and fresh dairy products may occur. The concentration of I-131 in milk from goats and sheep is 10 times higher than the concentration in cow's milk.
    • After I-131 ingestion, the most critical dietary information needed is
      • The amount and type of milk and milk products consumed
      • I-131 concentrations in the products
      • Time the products were consumed relative to the time of the release (which takes into account half-life and radioactive decay rate of I-131).
    • The easiest way to reduce or eliminate internal contamination from I-131 following a release is to find an alternate source of food items produced outside the contamination zone.

References:

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How and When KI Protects


  • Potassium iodide (KI) blocks uptake of radioactive iodine by the thyroid gland.
  • KI protects only the thyroid from radioactive iodine uptake. KI does not provide protection for any other organs.
  • KI is effective as a radiation medical countermeasure only for internal contamination with radioactive iodine. KI does NOT prevent or treat problems due to internal contamination from any other isotope.
  • When to take KI
    • KI is highly effective if taken several hours before inhaled contamination with radioactive iodine.
    • Taking KI within 1 to 2 hours after inhalation of I-131 can block more than 90% of the radioactive iodine uptake by the thyroid.
    • If KI is taken more than 4 hours after inhalation of I-131, much less thyroid uptake of I-131 is blocked.
    • KI is even less effective at preventing radioiodine uptake by the thyroid if taken more than 12 hours of a time-limited contamination episode.
    • Since the protective effect of a single dose of KI lasts approximately 24 hours, repeat KI administration may be indicated for some members of the public where contamination is continuing or ongoing.
  • Figure 1 below shows the effectiveness of thyroid blocking achieved by administering stable iodine at different times before (only at 1.2 hours) or various times after a 4-hours intake (inhalation) of I-131.
    • It is a conceptual graphic that should NOT be used clinically.
    • Note that the y-axis is in arbitrary units of averted dose, not a specific dose.
      • The higher the number on the y-axis the more dose is averted.
      • 1.0 is 100% dose to thyroid averted.
    • Dietary iodine intakes in the caption of Figure 1 refers to intake of stable KI, not I-131.

    Figure 1. Averted dose as a function of time stable iodine is administered relative to a 4-h intake of 131I for different dietary iodine intakes
    Graph demonstrating conceptually the effectiveness of thyroid blocking achieved by administering stable iodine
    Source: Guidelines for iodine prophylaxis following nuclear accidents, (PDF - 96 KB) (WHO, 1999, page 20, Figure 1)

  • Figure 2 below is another representation of KI effectiveness in relation to when KI tablets were taken before or after release of I-131 into the atmosphere.
    • Avant = before release of I-131 into the atmosphere
    • Après = after release of I-131 into the atmosphere
    • 100% refers to percent effective in averting dose.
    • It is a conceptual graphic that should NOT be used clinically.

    Figure 2. KI effectiveness as a function of intake time regarding exposure
    KI effectiveness as a function of intake time regarding exposure
    Source: Medical Effectiveness of Iodine Prophylaxis in a Nuclear Reactor Emergency Situation and Overview of European Practices, (European Commission, Directorate-General for Energy, Radiation Protection No. 165, page 33, 2010, [RISKAUDIT IRSN/GRS International in collaboration with Institut de Radioprotection et de Sû Nuclére (IRSN) France], under contract TREN/08/NUCL/SI2.520028], Jourdain JR (IRSN), Technical Project Leader, Herviou K [IRSN]). (PDF - 717 KB)

  • Both Figure 1 and Figure 2 suggest that there is a limited time window for maximal effectiveness of treatment with KI

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Prescribing Information


  • FDA-approved KI products come in two different forms:
    • Tablets: Both the 65- and 130-mg tablets are scored so they may be cut into smaller pieces to give lower doses
    • Liquid: Each milliliter (mL) of the oral liquid solution contains 65 mg of KI
  • FDA-approved marketed KI products:
    • Iosat tablets, 130 mg (scored in halves)
    • ThyroSafe tablets, 65 mg (scored in fourths)
    • ThyroShield oral solution, 65 mg/mL
  • Helping children take KI
  • Adults >40 years of age internally contaminated with ≥500 cGy of radioactive iodine
    • Have the lowest risk of developing thyroid cancer or thyroid injury from radioactive iodine contamination
    • Have a greater risk of having an allergic reaction to KI (compared to younger persons)
  • Adults >18 years of age, but ≤40 years of age internally contaminated with ≥10 cGy of radioactive iodine
    • Less sensitive to the effects of radioactive iodine than persons ≤18 years of age
  • Pregnant women (regardless of age) internally contaminated with ≥5 cGy radioactive iodine
    • Should take KI to protect both their own thyroid gland and the thyroid gland of the fetus
    • Should take only one dose of KI unless primary public health protection measures (evacuation, sheltering, and control of the food supply) are unavailable
    • Repeat dosing should be on the advice of public health authorities
  • Breast feeding women internally contaminated with ≥5 cGy radioactive iodine
    • Should take KI to protect both their own thyroid gland; any KI passed into breast milk is insufficient to protect nursing infants.
    • Should take only one dose of KI unless primary public health protection measures (evacuation, sheltering, and control of the food supply) are unavailable
    • Repeat dosing should be on the advice of public health authorities
    • Should stop breast feeding and switch to using baby formula or other food, per CDC recommendations
    • Should continue nursing if breast milk is the only food available for their infant
    • When nursing women receive >1 dose of KI, neonates not switched to formula or other food require monitoring for hypothyroidism.
  • Children ≤18 years of age internally contaminated with ≥5 cGy radioactive iodine
    • Most sensitive population to the potentially harmful effects of radioactive iodine
    • See chart for dosing (based on age)
    • Young persons ≤18 years of age but ≥150 pounds (70 kg) should take full adult dose of 130 mg, regardless of age
  • Neonates and infants internally contaminated with ≥5 cGy radioactive iodine
    • Are at greatest risk of radioactive iodine uptake through breast milk; it is best to discontinue breast feeding when possible.
    • Any KI passed into breast milk is insufficient to protect nursing infants from radioactive iodine.
    • Should take only one dose of KI unless primary public health protection measures (evacuation, sheltering, and control of the food supply) are unavailable.
    • Repeat dosing should be on the advice of public health authorities.
    • KI will help protect neonates and infants from inhaled or ingested radioactive iodine.
    • FDA strongly recommends monitoring of neonates and infants for potential hypothyroidism particularly when
      • Nursing mother receives > 1 dose of KI
      • Infants < 1 month of age receives any KI
      • Neonates receive more than 1 dose of KI
      • Neonates or infants with at risk mothers are not switched from breast milk to formula or other food

  • Dose recommendations for KI (FDA Guidance, December 2001)

    Print as PDF View/Print as PDF (PDF - 56 KB)

     

    Predicted thyroid exposure (cGy)

    KI dose (mg)

    Number or fraction of 130 mg tablets

    Number or fraction of 65 mg tablets

    Milliliters (mL) of oral solution, 65 mg/mL

    Adults over 40 years

    ≥ 500**

    130

    1

    2

    2 mL

    Adults over 18 through 40 years

    ≥ 10**

    130

    1

    2

    2 mL

    Pregnant or Lactating Women

    ≥ 5

    130

    1

    2

    2 mL

    Adolescents, 12 through 18 years*

    ≥ 5

    65

    1/2

    1

    1 mL

    Children over 3 years through 12 years

    ≥ 5

    65

    1/2

    1

    1 mL

    Children 1 month through 3 years

    ≥ 5

    32

    1/4

    1/2

    0.5 mL

    Infants birth through 1 month

    ≥ 5

    16

     

    1/4

    0.25 mL

    *Adolescents approaching adult size (≥70 kg) should receive the full adult dose (130 mg).
    **FDA understands that a KI administration program that sets different projected thyroid radioactive dose thresholds (committed dose equivalent (CDE)) for treatment of different population groups may be logistically impractical to implement during a radiological emergency. If emergency planners reach this conclusion, FDA recommends that KI be administered to both children and adults at the lowest intervention threshold (i.e. > 5 rem projected internal thyroid dose in children (FDA 2001)). Planning Guidance for Protection and Recovery Following Radiological Dispersal Device (RDD) and Improvised Nuclear Device (IND) Incidents (PDF - 519 KB) (DHS/FEMA, published in Federal Register, August 1, 2008, Z-RIN 1660-ZA02)

    References for dosing information:

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Duration of Therapy


  • In situations involving continuing or ongoing contamination
    • If primary public health protection measures (evacuation, sheltering, and control of the food supply) cannot be readily put into place, multi-dosing of KI may be required, sometimes up to 7-14 days.
    • Incident managers and public health experts will provide advice appropriate to the radiation event.
  • Once the plume has passed and/or public health protection measures (including distribution of KI) have been put place, prevention of internal contamination with radioiodines is best accomplished by food control measures and NOT by repeated dosing with KI.
  • Because radioactive iodine has a short half-life, 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 delayed consumption is not required.

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Contraindications to KI


  • KI should not be given to individuals with known iodine sensitivity.
  • A seafood or shellfish allergy does not necessarily indicate allergy to iodine.
  • KI should not be given to individuals with certain skin disorders (such as dermatitis herpetiformis or hypocomplementemic or urticaria vasculitis).
  • KI should be used with caution and with careful medical monitoring in individuals with thyroid disease (such as multinodular goiter, Graves disease, and autoimmune thyroiditis), especially if dosing extends beyond a few days. Such individuals should have monitoring of thyroid function.

Reference:


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How to Follow Patients Exposed to I-131



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How to Get KI?


  • Obtain from state, local, and federal agencies
  • KI is available at commercial pharmacies as an over-the counter product, but consumers should be wary of products that are not FDA-approved.
  • 3 FDA-approved potassium iodide (KI) products for use as an adjunct to other public health protective measures in the event that radioactive iodine is released into the environment.

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References


CDC resources

  1. Case Studies in Environmental Medicine (CSEM): Radiation Exposure from Iodine 131, Course SS3117. (HHS/ATSDR, November 2002)
  2. Radiation and Potassium Iodide (KI) (HHS/CDC, March, 2011)
  3. Potassium Iodide (KI) (HHS/CDC, March, 2011)

FDA resources

  1. Guidance: Potassium Iodide as a Thyroid Blocking Agent in Radiation Emergencies (PDF - 40 KB) (HHS/FDA)
  2. Other KI resources (HHS/FDA)
  3. Frequently Asked Questions on Potassium Iodide (KI) (HHS/FDA, March 2011)
  4. Home Preparation Procedure for Emergency Administration of Potassium Iodide Tablets to Infants and Small Children (HHS/FDA)

Pediatric information resources

  1. American Academy of Pediatrics Committee on Environmental Health. Radiation disasters and children. Pediatrics. 2003 Jun;111(6 Pt 1):1455-66. [PubMed Citation]
  2. Pediatric Counter-terrorism Measures (HHS/FDA, 2/2010) See KI information.

Other agencies

  1. How Potassium Iodide, or KI, Works (1:12 min) (DOE/ORISE/REAC/TS) Watch video
  2. Medical Effectiveness of Iodine Prophylaxis in a Nuclear Reactor Emergency Situation and Overview of European Practices, (European Commission, Directorate-General for Energy, Radiation Protection No. 165, page 33, 2010, [RISKAUDIT IRSN/GRS International in collaboration with Institut de Radioprotection et de Sû Nuclére (IRSN) France], under contract TREN/08/NUCL/SI2.520028], Jourdain JR (IRSN), Technical Project Leader, Herviou K [IRSN]). (PDF - 717 KB)
  3. Triage, Monitoring and Treatment - Handbook for management of the public in the event of malevolent use of radiation (Registration required for download) (TMT Handbook Partners)
  4. Radioactive Iodine in the Problem of Radiation Safety, Moscow, Atomizdat, 1972, editor L.A. Il'in, translated from Russian and published in English by the US Atomic Energy Commission, Office of Information Services in 1974 as document AECF-tr-7536, see especially page 224.)
  5. Radiological and Nuclear Incidents, U.S. Department of State, April, 2006
  6. Federal Policy on Use of Potassium Iodide (KI) (PDF - 43 KB) (DHS/FEMA document, published in Federal Register January 10, 2002)
  7. Use of Potassium Iodide for Thyroid Protection During Nuclear or Radiological Emergencies (WHO, March 2011)
  8. Guidelines for Iodine Prophylaxis Following Nuclear Accidents, (PDF - 96 KB) (WHO, 1999)

National Council on Radiation Protection and Measurements (NCRP)

  1. Management of Persons Contaminated with Radionuclides: Handbook (NCRP Report No. 161, Vol. I), National Council on Radiation Protection and Measurements, Bethesda, MD, 2008, Medical Treatments Arranged by Radionuclide (pp. 212-221).
  2. Management of Persons Contaminated with Radionuclides: Scientific and Technical Bases (NCRP Report No. 161, Vol. II), National Council on Radiation Protection and Measurements, Bethesda, MD, 2010, Health Effects from Radiation Exposure (p. 339), Iodine (pp. 594-604).
  3. Management of Persons Accidentally Contaminated with Radionuclides (NCRP Report No. 65), National Council on Radiation Protection and Measurements, Bethesda, MD, 1980. [NCRP 65 has been superseded by NCRP 161.]
  4. Risk to the Thyroid from Ionizing Radiation (NCRP Report No. 159), National Council on Radiation Protection and Measurements, Bethesda, MD, 2008.
 

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