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  1. Pharmacology. Iodine 131 is a product of fission reactions and likely to be a major form of internal radioactive contamination after a major nuclear reactor accident or weapon detonation.

    Potassium iodide (KI) blocks thyroid gland uptake of the radioactive isotopes of iodine by both diluting the radioactive iodine and “filling” the gland with nontoxic iodine. The radioactive molecules are subsequently excreted in the urine.

    For optimal protection, KI should be administered before or at the time of exposure to radioactive iodines but will have protective effects if initiated up to 4 hours after exposure. Daily administration is indicated until the risk for exposure to radioactive iodines no longer exists.

  2. Indications. Potassium iodide is indicated for prevention of uptake of radioactive isotopes of iodine by the thyroid gland. Note: KI should be used only when and if directed by federal, state, or local public health officials.

  3. Contraindications

    1. Known iodine allergy. Persons with the rare disorders of dermatitis herpetiformis and hypocomplementemic vasculitis are at increased risk for sensitivity.

    2. Iodine may be used in pregnant women, infants, and children, but safety has not been clearly established (see Section IV below).

  4. Adverse effects

    1. Gastrointestinal upset, diarrhea, burning of throat, metallic taste in mouth, and rarely inflammation of the salivary glands. These effects become more common as duration of therapy and dose increase.

    2. Allergic reactions ranging from skin rashes to respiratory distress may occur, although life-threatening reactions are very uncommon.

    3. Iodine-induced thyrotoxicosis, hypothyroidism, and goiter may occur, but incidence is less than 2%, even if therapy is used for longer durations.

    4. A bluish skin discoloration involving sweat glands may occur after large doses of iodine-containing products.

    5. Use in pregnancy. FDA Category D (See Phenytoin and Fosphenytoin). KI crosses the placental barrier and may cause hypothyroidism and goiter in the fetus. Risk is minimal with short-term use (˜10 days) and when given long before term.

    6. Use in neonates. Because of the increased risk for hypothyroidism in neonates (<1 month old), thyroid function tests should be monitored.

    7. Use in breastfeeding. KI passes into breast milk, but because radioiodines also pass into breast milk, lactating mothers should be cautioned to not breastfeed infants unless no other alternative is available.

  5. Drug or laboratory interactions

    1. Synergistic hypothyroid activity with lithium.

    2. Thyroid-stimulating hormone (TSH) and free thyroxine (T4) monitoring of thyroid function is reliable in the setting of standard dosing of KI. Recommended in all neonates treated with KI.

    3. Risk for hyperkalemia with prolonged use along with other potassium supplements and potassium-sparing medications (eg, spironolactone). However, the daily dose of potassium from KI is only about 3–4 mEq.

  6. Dosage and method of administration

    1. There are various dosing guidelines, including those recommended by the US Food and Drug Administration (FDA) and the World Health Organization (WHO). Public health officials should decide on the regimen they will use in a specific situation. A guidance document from the CDC is available at http://www.bt.cdc.gov/radiation/ki.asp.

    2. Adults older than 18 years, 130 mg orally once a day. Oral daily doses for other ages: adolescents and children (from 3–18 ...

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