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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)

    Figure 3. Protection of the thyroid gland by KI from inhaled iodine-131 as a function of the time of administration
    Protection of the thyroid gland by KI from inhaled iodine-131 as a function of the time of administration
    Source: Medical Management of Persons Internally Contaminated with Radionuclides in a Nuclear or Radiological Emergency, A Manual for Medical Personnel (See Section 4.2) (IAEA and partners, 2018)

  • Figure 1, Figure 2, and Figure 3 suggest that there is a limited time window for maximal effectiveness of treatment with KI
    • In Figure 3 above, the x-axis is time before or after internal contamination with radioactive iodine, and the y axis, represents % uptake avoided by taking the KI at the time noted.
    • As shown in Figure 3 above from the IAEA document
      • "KI is most effective if it is taken shortly before or shortly after internal contamination occurs, as illustrated by the graph in Figure 3."
      • "If promptly administered, KI will saturate the thyroid with non-radioactive iodine so that the radioactive iodine isotope, inhaled or ingested, will pass through the body instead of being taken up by the thyroid and subsequently irradiating it."

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Prescribing Information


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Duration of Therapy


  • FDA information on "how long should potassium iodide (KI) be taken?"
    • Since KI protects for approximately 24 hours, it should be dosed daily until the risk no longer exists.
    • Priority with regard to evacuation and sheltering should be given to pregnant females and neonates because of the potential for KI to suppress thyroid function in the fetus and neonate.
    • Unless other protective measures are not available, FDA does not recommend repeat dosing in pregnant females and neonates.
  • 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


  • FDA information about "who should NOT take potassium iodide or have restricted use"
    • 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.
    • A seafood or shellfish allergy does not necessarily mean that you are allergic or hypersensitive to iodine.
    • People with nodular thyroid with heart disease should not take KI. Individuals with multinodular goiter, Graves' disease, and autoimmune thyroiditis should be treated with caution -- especially if dosing extends beyond a few days.
    • If you are not sure if you should take KI, consult your healthcare professional.

Reference:


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What are the Side Effects of KI?


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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.
  • Search FDA-approved potassium iodide (KI) products (Type "Potassium Iodide" into the search box labeled "Find Approved Drugs") for use as an adjunct to other public health protective measures in the event that radioactive iodine is released into the environment.
    • FDA-approved products as of December, 2016
      Appl No Reference
      Listed
      Drug (RLD)             		Active Ingredient Dosage Form; Route Strength Proprietary Name Applicant
      A206211 No POTASSIUM IODIDE SOLUTION; ORAL 65MG/ML POTASSIUM IODIDE MISSION PHARMACAL CO
      A077218 Yes POTASSIUM IODIDE SOLUTION; ORAL 65MG/ML THYROSHIELD ARCO PHARMS LLC
      N018664 Yes POTASSIUM IODIDE TABLET; ORAL 130MG IOSAT ANBEX
      N018664 No POTASSIUM IODIDE TABLET; ORAL 65MG IOSAT ANBEX
      A076350 Yes POTASSIUM IODIDE TABLET; ORAL 65MG THYROSAFE RECIP

    • Contact manufacturers

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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. Potassium Iodide: Introductory Information (YouTube - 3:07 minutes) (HHS/CDC) Watch video
  3. Radiation and Potassium Iodide (KI) (HHS/CDC, March, 2011)
  4. Potassium Iodide (KI) (HHS/CDC, March, 2011)

FDA resources

  1. Potassium Iodide (KI): Instructions to Make Potassium Iodide Solution for Use During a Nuclear Emergency (Liquid Form) and KI Palatability and Stability References (March, 2018)
  2. Frequently Asked Questions on Potassium Iodide (KI) (October, 2016)
  3. Pediatric Medical Countermeasures – Considerations for Radiation Emergencies (September, 2018)
  4. FDA approved potassium iodide (KI) products (Type "Potassium Iodide" into search box)

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 Medical Countermeasures – Considerations for Radiation Emergencies (HHS/FDA, September, 2018)
  3. Potassium Iodide (KI): Instructions to Make Potassium Iodide Solution for Use During a Nuclear Emergency (Liquid Form) and KI Palatability and Stability References (HHS/FDA, March, 2018)

Other agencies

  1. 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)
  2. Triage, Monitoring and Treatment of people exposed to ionising radiation following a malevolent act (PDF - 11 MB) (TMT Handbook Partners, March 2009)
  3. 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.)
  4. Federal Policy on Use of Potassium Iodide (KI) (PDF - 43 KB) (DHS/FEMA document, published in Federal Register January 10, 2002)
  5. Iodine Thyroid Blocking: Guidelines for Use in Planning for and Responding to Radiological and Nuclear Emergencies (WHO, November 2017)
  6. Use of Potassium Iodide for Thyroid Protection During Nuclear or Radiological Emergencies (WHO, March 2011)
  7. 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: 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).
  2. Uncertainties in Internal Radiation Dose Assessment (NCRP Report No. 164), National Council on Radiation Protection and Measurements, Bethesda, MD, 2009.
  3. 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).
  4. Risk to the Thyroid from Ionizing Radiation (NCRP Report No. 159), National Council on Radiation Protection and Measurements, Bethesda, MD, 2008.
  5. 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.]

International Guidance

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