This segment introduces potassium iodide and discusses its indications, administration, adverse effects, and some special considerations. Afterwards, there is the option to apply what you have learned within a case study. 

[Description]

Potassium iodide (KI) is a salt of stable, non-radioactive, iodine that can help block radioactive iodine from being absorbed by the thyroid gland. It acts as a blocking agent by directly competing against radioactive iodine for absorption by the thyroid. By taking KI before or immediately after exposure to radioactive iodine, the thyroid can be significantly protected from radiation injury. This protection only extends to the thyroid, however, and other body parts are not protected by the use of potassium iodide.

[Availability]

Only Food and Drug Administration-approved preparations of potassium iodide should be used. All of these products are available over the counter without a prescription.

Their availability is not guaranteed, however, and shortages may occur during periods of high demand. Other sources of KI may include state or federal stockpiles, which could be distributed as needed during an emergency.

Other iodine containing preparations, such as saturated solution of potassium iodide (also called SSKI) or Lugol's solution, should not be substituted for FDA-approved preparations. Use of SSKI or Lugol's solution is not recommended  after exposure to radioactive iodine.

[Indications]

Use of KI should be considered after exposure to radioactive iodine, or when the possibility of such exposure exists.

In general, exposure to radioactive iodine is more likely to occur with nuclear plant accidents or improvised nuclear device (IND) scenarios, as opposed to radiation dispersal device scenarios. 

As you can see in the following chart, early administration can provide nearly 100% blockade of radioactive iodine absorption by the thyroid. These benefits decrease substantially with time after exposure. Once administered, a single dose of KI provides protection for 24 hours. Potassium iodide is therefore also protective up to 24 hours prior to anticipated exposure to radioactive iodine.

The Food and Drug Administration provides guidance on use of KI that prioritizes groups based on age, which primarily determines risk for radioiodine-induced thyroid cancer. Those at highest risk are infants and children, as well as pregnant and nursing women, and the recommendation is to treat them at the lowest threshold (with respect to predicted radiation dose to the thyroid). Anyone over age 18 and up to age 40 should be treated at a slightly higher threshold. Finally, anyone over 40 should be treated with KI only if the predicted radiation dose is high enough to destroy the thyroid and induce lifelong hypothyroidism. For ease of use, the specific indications for different groups are combined with dosing recommendations on the chart in the next section.

[Dosing and Administration]

All forms of KI are taken orally. KI may be available in tablet or liquid forms, and tablets can be dissolved in liquid for easier administration.

The following chart provides detailed recommendations on the exposure levels indicating KI use and the appropriate doses for different groups. Notice that while pregnant women, adults ages 18-40, and adults over 40 all take the same 130 mg dose of KI, the indication for each group is different and based on the amount of radiation exposure to the thyroid. Adults over 40 have much higher dose thresholds for treatment (5 Gy) than adults under 40 (0.1 Gy). Furthermore, pregnant women have even lower thresholds (0.05 Gy), the same threshold level as children and infants. Recommended doses are based on patient weight, so adolescents approaching adult size, or greater than 150 pounds, should receive the full adult dose of 130 mg.

When administering KI to young children, consider various methods of flavoring to encourage intake. Popular options include raspberry syrup, chocolate milk, orange juice, or flat sodas.

[Monitoring and Follow-up]

Individuals that receive KI should be monitored for allergic and other adverse reactions.

Neonates taking KI should be monitored for signs of hypothyroidism, and may warrant laboratory testing of thyroid hormone levels if they receive more than one dose of KI.

[Adverse effects]

The adverse effects of KI use are more likely seen if a person:

• Takes a higher dose than recommended

• Takes KI for several days

• Has pre-existing thyroid disease

Adverse effects may include gastrointestinal upset, allergic reactions, rashes, and inflammation of the salivary glands. Individuals may also experience "iodism", which includes a metallic taste, a burning sensation in the mouth and throat, sore teeth and gums, symptoms of an upper respiratory infection, and sometimes upset stomach and diarrhea.

Infants less than one month old who receive more than one dose of KI are at risk for developing hypothyroidism.

[Contraindications]

Contraindications to potassium iodide include:

• Allergy to iodine

• Dermatitis herpetiformis

• Urticarial vasculitis

• Nodular thyroid with accompanying heart disease

Please note that allergy to shellfish, povidone-iodine, or to radiocontrast media is not equivalent to iodine allergy. KI may be safely administered to individuals reporting these allergies . Also, both dermatitis herpetiformis and urticarial vasculitis are very rare conditions.

[Special Considerations]

There are some special considerations when administering KI.

• For infants  or pregnant or breastfeeding women, note that certain dose limits may apply to minimize the risk of complications such as hypothyroidism.

• Adults over 40 years old have less risk of thyroid injury and cancer after exposure to radioiodine, and an increased likelihood of adverse reactions to KI. As such, the following considerations apply to this population:

• Treatment with KI should only occur if radiation exposure is high enough to potentially cause lifelong hypothyroidism.

• Caution should be applied when treating individuals with multinodular goiter, Graves' disease, and autoimmune thyroiditis.

• Internal contamination with radioactive iodine may occur after an incident when an individual eats food items that have been contaminated (e.g. agricultural products, milk from cows fed on open pastures, and sources of drinking water). Caution should be taken to avoid consuming materials that might have been contaminated.

If you would like more information regarding KI, please consult the additional resources links at the end of the course.