Hans Howe

Nuclear accidents

In 1982, the U.S. Food and Drug Administration approved potassium iodide to protect thyroid glands from radioactive iodine involving accidents or fission emergencies.[citation
needed] In an accidental event or attack on a nuclear power plant, or in nuclear bomb fallout, volatile fission product radionuclides may be released. Of these products, 131
I
is one of the most common and is particularly dangerous to the thyroid gland because it may lead to thyroid cancer.[citation
needed] By saturating the body with a source of stable iodide prior to exposure, inhaled or ingested 131
I
tends to be excreted, which prevents radioiodine uptake by the thyroid. According to one 2000 study “KI administered up to 48 h before 131
I
exposure can almost completely block thyroid uptake and therefore greatly reduce the thyroid absorbed dose. However, KI administration 96 h or more before 131
I
exposure has no significant protective effect. In contrast, KI administration after exposure to radioiodine induces a smaller and rapidly decreasing blockade effect.”[18] For optimal prevention, KI must be dosed daily until a risk of significant exposure to radioiodine by either inhalation or ingestion no longer exists.

Emergency 130 milligrams potassium iodide doses provide 100 mg iodide (the other 30 mg is the potassium in the compound), which is roughly 700 times larger than the normal nutritional need (see recommended dietary allowance) for iodine, which is 150 micrograms (0.15 mg) of iodine (as iodide) per day for an adult. The typical tablet actually weighs 160 mg. 130 mg of which is potassium iodide, and 30 mg being excipients, such as binding agents.

Potassium iodide cannot protect against any other causes of radiation poisoning, nor can it provide any degree of protection against dirty bombs that produce radionuclides other than those of iodine.

[19]

Age KI in mg per day Over 12 years old 130 3 – 12 years old 65 1 – 36 months old 32 < 1 month old 16 The potassium iodide in iodized salt is insufficient for this use.[20] A likely lethal dose of salt (more than a kilogram[21]) would be needed to equal the potassium iodide in one tablet.[22]

The World Health Organization does not recommend KI prophylaxis for adults over 40 years, unless the radiation dose from inhaled radioiodine is expected to threaten thyroid function, because the KI side effects increase with age and may exceed the KI protective effects; “…unless doses to the thyroid from inhalation rise to levels threatening thyroid function, that is of the order of about 5 Gy. Such radiation doses will not occur far away from an accident site.”[19]

The U.S. Department of Health and Human Services restated these two years later as “The downward KI (potassium iodide) dose adjustment by age group, based on body size considerations, adheres to the principle of minimum effective dose. The recommended standard (daily) dose of KI for all school-age children is the same (65 mg). However, adolescents approaching adult size (i.e., >70 kg [154 lbs]) 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.”[23]

SSKI (i.e., the solution of KI rather than tablets) may be used in radioiodine-contamination emergencies (i.e., nuclear accidents) to “block” the thyroid’s uptake of radioiodine, at a dose of two drops of SSKI per day for an adult. This is not the same as blocking the thyroid’s release of thyroid hormone, for which the adult dose is different (and is actually higher by a factor of 7 or 8), and for which KI anti-radiation pills (not a common medical treatment form of KI) are not usually available in pharmacies, or normally used in hospitals, or by physicians. Although the two forms of potassium iodide are completely interchangeable, normally in practice the SSKI solution, which is the historical medical form of high dose iodine, is generally used for all medical purposes save for radioiodine prophylaxis. For protection of the thyroid against radioiodine (iodine-131) contamination, the convenient standard 130 mg KI pill is used, if available. As noted, the equivalent two drops of SSKI (equaling the dose of one KI pill) may be used for this purpose, if the pills are not available.

https://en.wikipedia.org/wiki/Potassium_iodide#Nuclear_accidents

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