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| Clinical data | |
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| Trade names | Iosat, Thyrosafe, Thyroshield, others |
| Other names | SSKI |
| AHFS/Drugs.com | Monograph |
| License data | |
| Routes of administration | By mouth |
| ATC code | |
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| Identifiers | |
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| CompTox Dashboard(EPA) | |
| ECHA InfoCard | 100.028.782 |
| Chemical and physical data | |
| Formula | KI |
| 3D model (JSmol) | |
| Density | 3.13[1] g/cm3 |
| Melting point | 681 °C (1,258 °F) |
| Boiling point | 1,330 °C (2,430 °F) |
| Solubility in water | 1280 mg/mL (0 °C (32 °F)) 1400 mg/mL (20 °C (68 °F)) 1760 mg/mL (60 °C (140 °F)) 2060 mg/mL (100 °C (212 °F)) |
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Potassium iodide is achemical compound,medication, anddietary supplement.[3][4] It is a medication used for treatinghyperthyroidism, inradiation emergencies, and for protecting thethyroid gland when certain types ofradiopharmaceuticals are used.[5] It is also used for treating skinsporotrichosis andphycomycosis.[5][6] It is a supplement used by people with low dietary intake ofiodine.[4] It is administered orally.[5]
Common side effects include vomiting, diarrhea, abdominal pain, rash, and swelling of thesalivary glands.[5] Other side effects includeallergic reactions,headache,goitre, anddepression.[6] While use duringpregnancy may harm the baby, its use is still recommended in radiation emergencies.[5] Potassium iodide has thechemical formulaKI.[7] Commercially it is made by mixingpotassium hydroxide with iodine.[8][9]
Potassium iodide has been used medically since at least 1820.[10] It is on theWorld Health Organization's List of Essential Medicines.[11] Potassium iodide is available as ageneric medication andover the counter.[12] Potassium iodide is also used for theiodization of salt.[4]
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 iodizingtable salt (a public health measure to preventiodine deficiency in populations that get little seafood). The oxidation of iodide causes slow loss of iodine content fromiodised 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.[13]Potassium iodate (KIO3) is used to iodize some salts so that the iodine is not lost by oxidation.Dextrose orsodium thiosulfate are often added to iodized table salt to stabilize potassium iodide thus reducing loss of the volatile chemical.[14]
Thyroid iodine uptake blockade with potassium iodide is used innuclear medicinescintigraphy and therapy with some radioiodinated compounds that are not targeted to the thyroid, such asiobenguane (MIBG), which is used to image or treat neural tissue tumors, or iodinatedfibrinogen, which is used infibrinogen 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 (WHO) provides guidelines for potassium iodide use following a nuclear accident. The dosage of potassium iodide is age-dependent: neonates (<1 month) 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.[15] These dosages list mass of potassium iodide rather than elemental iodine.[16][15] Potassium iodide can be administered as tablets or asLugol's iodine solution.[15] The same dosage is recommended by the USFood and Drug Administration.[17] A single daily dose is typically sufficient for 24-hour protection.[15] However, in cases of prolonged or repeated exposure, health authorities may recommend multiple daily doses.[15] Priority for prophylaxis is given to the most sensitive groups: pregnant and breastfeeding women, infants, and children under 18 years.[15] The recommended doses of potassium iodide, which contains a stable isotope of iodine, only protect the thyroid gland from radioactive iodine.[15] It does not offer protection against other radioactive substances.[15] Some sources recommend alternative dosing regimens.[specify][18]
Not all sources are in agreement on the necessaryduration of thyroid blockade, although agreement appears to have been reached about thenecessity of blockade for bothscintigraphic and therapeutic applications of iobenguane. Commercially available iobenguane is labeled withiodine-123, and product labeling recommends administration of potassium iodide 1 hour prior to administration of the radiopharmaceutical for all age groups,[19] while theEuropean Association of Nuclear Medicine recommends (for iobenguane labeled with either isotope), 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.[18][20]
Product labeling for diagnosticiodine-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.[21] 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.[22]
| 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 protectthyroid glands fromradioactive iodine involving accidents or fission emergencies. In an accidental event or attack on anuclear power plant, or innuclear bomb fallout, volatilefission productradionuclides may be released. Of these products,131
I (Iodine-131) is one of the most common and is particularly dangerous to the thyroid gland because it may lead tothyroid cancer.[24] By saturating the body with a source of stable iodide prior to exposure, inhaled or ingested131
I tends to be excreted, which prevents radioiodine uptake by the thyroid. According to one 2000 study "KI administered up to 48 h before131
I exposure can almost completely block thyroid uptake and therefore greatly reduce the thyroid absorbed dose. However, KI administration 96 h or more before131
I exposure has no significant protective effect. In contrast, KI administration after exposure to radioiodine induces a smaller and rapidly decreasing blockade effect."[25] 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.[26]
Emergency 130 milligrams potassium iodide doses provide 100 mg iodide (the other 30 mg is the potassium in the compound),[16] which is roughly 700 times larger than the normal nutritional need (seerecommended dietary allowance) for iodine, which is 150 micrograms (0.15 mg) of iodine (as iodide) per day for an adult. A typical tablet weighs 160 mg, with 130 mg of potassium iodide and 30 mg ofexcipients, such asbinding agents.[16]
Potassium iodide cannot protect against any other mechanisms ofradiation poisoning, nor can it provide any degree of protection againstdirty bombs that produce radionuclides other than those of iodine.[15]
The potassium iodide iniodized salt is insufficient for this use.[27] A likelylethal dose of salt (more than a kilogram[28]) would be needed to equal the potassium iodide in one tablet.[29]
TheWorld 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 5Gy. Such radiation doses will not occur far away from an accident site."[23][15]
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."[30]
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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 theJod-Basedow phenomenon, trigger and/or worsenhyperthyroidism andhypothyroidism, and then cause temporary or even permanent thyroid conditions. It can also causesialadenitis (an inflammation of the salivary gland), gastrointestinal disturbances, and rashes.
Potassium iodide is not recommended for people withdermatitis herpetiformis andhypocomplementemic vasculitis – conditions that are linked to a risk of iodine sensitivity.[31]
There have been some reports of potassium iodide treatment causing swelling of theparotid gland (one of the threeglands that secretesaliva), due to its stimulatory effects on saliva production.[32]
A saturated solution of KI (SSKI) is typically given orally in adult doses several times a day (5 drops of SSKI assumed to be1⁄3 mL) for thyroid blockade (to prevent the thyroid from excreting thyroid hormone) and occasionally this dose is also used, when iodide is used as an expectorant (the total dose is about one gram KI per day for an adult). The anti-radioiodine doses used for131
I uptake blockade are lower, and range downward from 100 mg a day for an adult, to less than this for children (see table). 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 (150 micrograms, not milligrams).
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 (especially during the first several days, as the body adjusts to the medication). More severe side effects that require notification of a physician are: fever, weakness, unusual tiredness, swelling in the neck or throat,[citation needed] mouth sores, skin rash, nausea, vomiting, stomach pains, irregular heartbeat,[citation needed] numbness or tingling of the hands or feet, or a metallic taste in the mouth.[33][citation needed]
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 againstcarcinogenic radioiodine bioaccumulation.
The ingestion of goitrogen drugs is, much like potassium iodide also not without its dangers, such ashypothyroidism. In all these cases however, despite the risks, the prophylaxis benefits of intervention with iodide, iodate or perchlorate outweigh the serious cancer risk from radioiodinebioaccumulation in regions where radioiodine has sufficiently contaminated the environment.
KI is used with silver nitrate to makesilver iodide (AgI), an important chemical in film photography. KI is a component in some disinfectants and hair treatment chemicals. KI is also used as afluorescence quenching agent in biomedical research, an application that takes advantage of collisional quenching of fluorescent substances by the iodide ion. However, for several fluorophores addition of KI in μM-mM concentrations results in increase of fluorescence intensity, and iodide acts as fluorescence enhancer.[34]
Potassium iodide is a component in the electrolyte ofdye sensitised solar cells (DSSC) along with iodine.
Potassium iodide finds its most important applications in organic synthesis mainly in the preparation of aryl iodides in theSandmeyer reaction, starting from aryl amines. Aryl iodides are in turn used to attach aryl groups to other organics by nucleophilic substitution, with iodide ion as the leaving group.
Potassium iodide is anionic compound which is made of the followingions:K+I−. It crystallises in thesodium chloride structure. It is produced industrially by treating KOH with iodine.[35]
It is a whitesalt, which is the most commercially significant iodide compound, with approximately 37,000 tons produced in 1985. It absorbs water less readily thansodium iodide, making it easier to work with.
Aged and impure samples are yellow because of the slowoxidation of the salt topotassium carbonate and elementaliodine.[35]
Since theiodide ion is a mildreducing agent,I− is easily oxidised toiodine (I2) by powerfuloxidising agents such aschlorine:
This reaction is employed in the isolation of iodine from natural sources. Air will oxidize iodide, as evidenced by the observation of a purple extract when aged samples of KI are rinsed withdichloromethane. As formed under acidic conditions,hydriodic acid (HI) is a stronger reducing agent.[36][37][38]
Like other iodide salts, KI formstriiodide (I−3) when combined with elementaliodine.
UnlikeI2,I−3 salts can be highly water-soluble. Through this reaction,iodine is used inredoxtitrations. AqueousKI3 (Lugol's iodine) solution is used as a disinfectant and as an etchant for gold surfaces.
Potassium iodide andsilver nitrate are used to makesilver(I) iodide, which is used for high speedphotographic film and forcloud seeding:
KI serves as a source of iodide inorganic synthesis. A useful application is in the preparation of aryl iodides fromarenediazonium salts.[39][40]
KI, acting as a source of iodide, may also act as anucleophilic catalyst for the alkylation of alkylchlorides,bromides, ormesylates.
Potassium iodide has been used medically since at least 1820.[10] Some of the earliest uses included cures forsyphilis,[10]lead andmercury poisoning.
Potassium iodide's (KI) value as a radiation protective (thyroid blocking) agent was demonstrated following theChernobyl nuclear reactor disaster in April 1986. A saturated solution of potassium iodide (SSKI) was administered to 10.5 million children and 7 million adults inPoland[30][41] as a preventative measure against accumulation of radioactive131
I in thethyroid gland.
Reports differ concerning whether people in the areas immediately surrounding Chernobyl itself were given the supplement.[42][20] However the US Nuclear Regulatory Commission (NRC) reported, "thousands of measurements of I-131 (radioactive iodine) activity...suggest that the observed levels were lower than would have been expected had this prophylactic measure not been taken. The use of KI...was credited with permissible iodine content in 97% of the evacuees tested."[20]
With the passage of time, people living in irradiated areas where KI was not available have developed thyroid cancer at epidemic levels, which is why the US Food and Drug Administration (FDA) reported "The data clearly demonstrate the risks of thyroid radiation... KI can be used [to] provide safe and effective protection against thyroid cancer caused by irradiation."[43]
Chernobyl also demonstrated that the need to protect the thyroid from radiation was greater than expected. Within ten years of the accident, it became clear that thyroid damage caused by released radioactive iodine was virtually the only adverse health effect that could be measured. As reported by the NRC, studies after the accident showed that "As of 1996, except for thyroid cancer, there has been no confirmed increase in the rates of other cancers, including leukemia, among the... public, that have been attributed to releases from the accident."[44]
But equally important to the question of KI is the fact that radioactivity releases are not "local" events. Researchers at the World Health Organization accurately located and counted the residents with cancer from Chernobyl and were startled to find that "the increase in incidence [of thyroid cancer] has been documented up to 500 km from the accident site... significant doses from radioactive iodine can occur hundreds of kilometers from the site, beyond emergency planning zones."[23] Consequently, far more people than anticipated were affected by the radiation, which caused the United Nations to report in 2002 that "The number of people with thyroid cancer... has exceeded expectations. Over 11,000 cases have already been reported."[45]
The Chernobyl findings were consistent with studies of the effects of previous radioactivity releases. In 1945, several hundreds of thousands of people working and residing in the Japanese cities ofHiroshima andNagasaki were exposed to high levels of radiation afteratomic bombs weredetonated over the two cities by the United States. Survivors of the A-bombings, also known ashibakusha, have markedly high rates of thyroid disease; a 2006 study of 4091hibakusha found nearly half the participants (1833; 44.8%) had an identifiable thyroid disease.[46]
An editorial inThe Journal of the American Medical Association regarding thyroid diseases in bothhibakusha and those affected by the Chernobyl disaster reports that "[a] straight line adequately describes the relationship between radiation dose and thyroid cancer incidence" and states "it is remarkable that a biological effect from a single brief environmental exposure nearly 60 years in the past is still present and can be detected."[47]
The development of thyroid cancer among residents in theNorth Pacific from radioactive fallout following theUnited States' nuclear weapons testing in the 1950s (on islands nearly 200 miles downwind of the tests) were instrumental in the 1978 decision by theFDA to issue a request for the availability of KI for thyroid protection in the event of a release from a commercial nuclear power plant or weapons-related nuclear incident. Noting that KI's effectiveness was "virtually complete" and finding that iodine in the form of KI was substantially superior to other forms includingiodate (KIO3) in terms of safety, effectiveness, lack of side effects, and speed of onset, the FDA invited manufacturers to submit applications to produce and market KI.[48]
It was reported on 16 March 2011, that potassium iodide tablets were given preventively to U.S. Naval air crew members flying within 70 nautical miles of theFukushima Daiichi Nuclear Power Plant damaged in the earthquake (8.9/9.0 magnitude) and ensuing tsunami on 11 March 2011. The measures were seen as precautions, and the Pentagon said no U.S. forces have shown signs of radiation poisoning. By 20 March, the US Navy instructed personnel coming within 100 miles of the reactor to take the pills.[49]
In the Netherlands, the central storage of iodine-pills is located inZoetermeer, nearThe Hague. In 2017, the Dutch government distributed pills to hundreds of thousands of residents who lived within a certain distance of nuclear power plants and met some other criteria.[50][51]
By 2020, potassium iodide tablets are made available free of charge for all residents in all pharmacies throughout the country.[52]
Three companies (Anbex, Inc., Fleming Co, andRecipharm of Sweden) have met the strict FDA requirements for manufacturing and testing of KI, and they offer products (IOSAT, ThyroShield, and ThyroSafe,[53] respectively) which are available for purchase. In 2012, Fleming Co. sold all its product rights and manufacturing facility to other companies and no longer exists. ThyroShield is currently not in production.
Tablets of potassium iodide are supplied for emergency purposes related to blockade of radioiodine uptake, a common form ofradiation poisoning due to environmental contamination by the short-lived fission product131
I.[54] Potassium iodide may also be administered pharmaceutically forthyroid storm.
For reasons noted above, therapeutic drops of SSKI, or 130 mg tablets of KI as used for nuclear fission accidents, are not used as nutritional supplements, since an SSKI drop or nuclear-emergency tablet provides 300 to 700 times more iodine than the daily adult nutritional requirement. Dedicated nutritional iodide tablets containing 0.15 mg (150 micrograms (μg)) of iodide, from KI or from various other sources (such as kelp extract) are marketed as supplements, but they are not to be confused with the much higher pharmaceutical dose preparations.
Potassium iodide can be conveniently prepared in a saturated solution, abbreviated SSKI. This method of delivering potassium iodide doesn't require a method to weigh out the potassium iodide, thus allowing it to be used in an emergency situation. KI crystals are simply added to water until no more KI will dissolve and instead sits at the bottom of the container. With pure water, the concentration of KI in the solution depends only on the temperature. Potassium iodide is highly soluble in water thus SSKI is a concentrated source of KI. At 20 degrees Celsius the solubility of KI is 140-148 grams per 100 grams of water.[55] Because the volumes of KI and water are approximately additive, the resulting SSKI solution will contain about 1.00 gram (1000 mg) KI per milliliter (mL) of solution. This is 100% weight/volume (note units ofmass concentration) of KI (one gram KI per mL solution), which is possible because SSKI is significantly more dense than pure water—about 1.67 g/mL.[56] Because KI is about 76.4% iodide by weight, SSKI contains about 764 mg iodide per mL. Thisconcentration of iodide allows the calculation of the iodide dose per drop, if one knows the number of drops per milliliter. For SSKI, a solution more viscous than water, there are assumed to be 15 drops per mL; the iodide dose is therefore approximately 51 mg per drop. It is conventionally rounded to 50 mg per drop.
The term SSKI is also used, especially by pharmacists, to refer to a U.S.P. pre-prepared solution formula, made by adding KI to water to prepare a solution containing 1000 mg KI per mL solution (100% wt/volume KI solution), to closely approximate the concentration of SSKI made by saturation. This is essentially interchangeable with SSKI made by saturation, and also contains about 50 mg iodide per drop.
