Potassium iodide

Potassium iodide is a chemical compound, medication, and dietary supplement. It is a medication used for treating hyperthyroidism, in radiation emergencies, and for protecting the thyroid gland when certain types of radiopharmaceuticals are used. It is also used for treating skin sporotrichosis and phycomycosis. It is a supplement used by people with low dietary intake of iodine. It is administered orally.
Common side effects include vomiting, diarrhea, abdominal pain, rash, and swelling of the salivary glands. Other side effects include allergic reactions, headache, goitre, and depression. While use during pregnancy may harm the baby, its use is still recommended in radiation emergencies. Potassium iodide has the chemical formula KI. Commercially it is made by mixing potassium hydroxide with iodine.
Potassium iodide has been used medically since at least 1820. It is on the World Health Organization's List of Essential Medicines. Potassium iodide is available as a generic medication and over the counter. Potassium iodide is also used for the iodization of salt.

Medical uses

Dietary supplement

Potassium iodide is a nutritional supplement in animal feeds and also in the human diet. In humans it is the most common additive used for iodizing table salt. The oxidation of iodide causes slow loss of iodine content from iodised salts that are exposed to excess air. The alkali metal iodide salt, over time and exposure to excess oxygen and carbon dioxide, slowly oxidizes to metal carbonate and elemental iodine, which then evaporates. Potassium iodate is used to iodize some salts so that the iodine is not lost by oxidation. Dextrose or sodium thiosulfate are often added to iodized table salt to stabilize potassium iodide thus reducing loss of the volatile chemical.

Thyroid protection in nuclear accidents

Thyroid iodine uptake blockade with potassium iodide is used in nuclear medicine scintigraphy and therapy with some radioiodinated compounds that are not targeted to the thyroid, such as iobenguane, which is used to image or treat neural tissue tumors, or iodinated fibrinogen, which is used in fibrinogen scans to investigate clotting. These compounds contain iodine, but not in the iodide form. Since they may be ultimately metabolized or break down to radioactive iodide, it is common to administer non-radioactive potassium iodide to ensure that iodide from these radiopharmaceuticals is not sequestered by the normal affinity of the thyroid for iodide.
The World Health Organization provides guidelines for potassium iodide use following a nuclear accident. The dosage of potassium iodide is age-dependent: neonates require 16 mg/day; children aged 1 month to 3 years need 32 mg/day; those aged 3-12 years need 65 mg/day; and individuals over 12 years and adults require 130 mg/day. These dosages list mass of potassium iodide rather than elemental iodine. Potassium iodide can be administered as tablets or as Lugol's iodine solution. The same dosage is recommended by the US Food and Drug Administration. A single daily dose is typically sufficient for 24-hour protection. However, in cases of prolonged or repeated exposure, health authorities may recommend multiple daily doses. Priority for prophylaxis is given to the most sensitive groups: pregnant and breastfeeding women, infants, and children under 18 years. The recommended doses of potassium iodide, which contains a stable isotope of iodine, only protect the thyroid gland from radioactive iodine. It does not offer protection against other radioactive substances. Some sources recommend alternative dosing regimens.
Not all sources are in agreement on the necessary duration of thyroid blockade, although agreement appears to have been reached about the necessity of blockade for both scintigraphic and therapeutic applications of iobenguane. Commercially available iobenguane is labeled with iodine-123, and product labeling recommends administration of potassium iodide 1 hour prior to administration of the radiopharmaceutical for all age groups, while the European Association of Nuclear Medicine recommends, that potassium iodide administration begin one day prior to radiopharmaceutical administration, and continue until the day following the injection, with the exception of new-borns, who do not require potassium iodide doses following radiopharmaceutical injection.
Product labeling for diagnostic iodine-131 iobenguane recommends potassium iodide administration one day before injection and continuing 5 to 7 days following administration, in keeping with the much longer half-life of this isotope and its greater danger to the thyroid. Iodine-131 iobenguane used for therapeutic purposes requires a different pre-medication duration, beginning 24–48 hours prior to iobenguane injection and continuing 10–15 days following injection.

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

In 1982, the U.S. Food and Drug Administration approved potassium iodide to protect thyroid glands from radioactive iodine involving accidents or fission emergencies. 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, is one of the most common and is particularly dangerous to the thyroid gland because it may lead to thyroid cancer. By saturating the body with a source of stable iodide prior to exposure, inhaled or ingested tends to be excreted, which prevents radioiodine uptake by the thyroid. According to one 2000 study "KI administered up to 48 h before exposure can almost completely block thyroid uptake and therefore greatly reduce the thyroid absorbed dose. However, KI administration 96 h or more before exposure has no significant protective effect. In contrast, KI administration after exposure to radioiodine induces a smaller and rapidly decreasing blockade effect." According to the FDA, KI should not be taken as a preventative before radiation exposure. Since KI protects for approximately 24 hours, it must be dosed daily until a risk of significant exposure to radioiodine no longer exists.
Emergency 130 milligrams potassium iodide doses provide 100 mg iodide, which is roughly 700 times larger than the normal nutritional need for iodine, which is 150 micrograms of iodine per day for an adult. A typical tablet weighs 160 mg, with 130 mg of potassium iodide and 30 mg of excipients, such as binding agents.
Potassium iodide cannot protect against any other mechanisms of radiation poisoning, nor can it provide any degree of protection against dirty bombs that produce radionuclides other than those of iodine.
The potassium iodide in iodized salt is insufficient for this use. A likely lethal dose of salt would be needed to equal the potassium iodide in one tablet.
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."
The U.S. Department of Health and Human Services restated these two years later as "The downward KI dose adjustment by age group, based on body size considerations, adheres to the principle of minimum effective dose. The recommended standard dose of KI for all school-age children is the same. However, adolescents approaching adult size should receive the full adult dose for maximal block of thyroid radioiodine uptake. Neonates ideally should receive the lowest dose of KI."

Side effects

There is reason for caution with prescribing the ingestion of high doses of potassium iodide and iodate, because their unnecessary use can cause conditions such as the Jod-Basedow phenomenon, trigger and/or worsen hyperthyroidism and hypothyroidism, and then cause temporary or even permanent thyroid conditions. It can also cause sialadenitis, gastrointestinal disturbances, and rashes.
Potassium iodide is not recommended for people with dermatitis herpetiformis and hypocomplementemic vasculitis – conditions that are linked to a risk of iodine sensitivity.
There have been some reports of potassium iodide treatment causing swelling of the parotid gland, due to its stimulatory effects on saliva production.
A saturated solution of KI is typically given orally in adult doses several times a day for thyroid blockade and occasionally this dose is also used, when iodide is used as an expectorant. The anti-radioiodine doses used for uptake blockade are lower, and range downward from 100 mg a day for an adult, to less than this for children. All of these doses should be compared with the far lower dose of iodine needed in normal nutrition, which is only 150 μg per day.
At maximal doses, and sometimes at much lower doses, side effects of iodide used for medical reasons, in doses of 1000 times the normal nutritional need, may include: acne, loss of appetite, or upset stomach. More severe side effects that require notification of a physician are: fever, weakness, unusual tiredness, swelling in the neck or throat, mouth sores, skin rash, nausea, vomiting, stomach pains, irregular heartbeat, numbness or tingling of the hands or feet, or a metallic taste in the mouth.
In the event of a radioiodine release the ingestion of prophylaxis potassium iodide, if available, or even iodate, would rightly take precedence over perchlorate administration, and would be the first line of defence in protecting the population from a radioiodine release. However, in the event of a radioiodine release too massive and widespread to be controlled by the limited stock of iodide and iodate prophylaxis drugs, then the addition of perchlorate ions to the water supply, or distribution of perchlorate tablets would serve as a cheap, efficacious, second line of defense against carcinogenic radioiodine bioaccumulation.
The ingestion of goitrogen drugs is, much like potassium iodide also not without its dangers, such as hypothyroidism. In all these cases however, despite the risks, the prophylaxis benefits of intervention with iodide, iodate or perchlorate outweigh the serious cancer risk from radioiodine bioaccumulation in regions where radioiodine has sufficiently contaminated the environment.