Potassium iodide (KI) is a medication and dietary supplement. As a dietary supplement, it has utility in patients with low iodine intake, a more frequent occurrence in developing countries. As a prescribed medication, it is used to treat severe hyperthyroidism, cutaneous inflammatory dermatoses, nuclear emergencies, and to protect the thyroid gland when using radiopharmaceuticals.
Concerning emergency radiation, the U.S. Nuclear Regulatory Commission (NRC) and the American Thyroid Association (ATA) require states to consider including KI as a protective measure. Its utilization is necessary when within a 10-mile radius of a nuclear along with adequate prevention methods such as evacuation, sheltering, and avoiding contaminated foods in the event of a nuclear accident. Furthermore, they state that KI must be available to state and local governments. The guidance titled "Potassium Iodide as a Thyroid Blocking Agent in Radiation Emergencies" from the Food Drug Administration (FDA) of the United States prioritizes age, which is the primary factor for determining risk for radioiodine-induced thyroid cancer after radiation exposure. Those at highest risk are infants, children, and pregnant and nursing females. The recommendation is to treat this population at the lowest threshold of the predicted radioactive dose to the thyroid. Any person over 18 years old and up to 40 years old should receive treatment at a slightly higher limit. Lastly, anyone over 40 years old should have KI treatment only if the predicted exposure level is high enough to destroy the thyroid, inducing lifelong hypothyroidism. KI works best if used within 3 to 4 hours of exposure. In the event of a nuclear accident, KI pills, taken once daily, decrease thyroid uptake of radioactive iodine. It almost protects the thyroid completely if administered within 12 hours before radioactive iodine exposure; after exposure, the degree of protection declines (80, 40, and 7 percent after 2, 8, and 24 hours, respectively).
In regards to patients with dermatoses, the two best indications in this group are neutrophilic dermatoses and panniculitis. Especially for lymphocutaneous and cutaneous sporotrichosis, itraconazole is the drug of choice for the treatment. However, patients who don't respond to itraconazole at 200 mg/day, can receive KI together with other antimycotics as an alternative. It is also successfully used for other inflammatory dermatoses. For instance, erythema nodosum, subacute nodular migratory panniculitis, nodular vasculitis, erythema multiforme, and Sweet syndrome.
KI has several mechanisms of action on thyroid function. In euthyroid patients, the iodine has two effects at two different times. The most rapid (hours to days) effect, at pharmacologic doses of KI, is to decrease thyroglobulin proteolysis, thereby decreasing thyroid hormone secretion. The resulting slight reductions of T4 and T3 concentrations in serum cause transient increases of thyrotropin (TSH) concentrations in serum. Secondly, KI inhibits thyroid hormone synthesis. The administration of KI leads to temporary inhibition of iodine organification in the thyroid gland, thereby decreasing thyroid hormone biosynthesis, a phenomenon called the Wolff-Chaikoff effect (WCE). However, within two to four weeks of continual exposure to excess iodine, organification, and thyroid hormone biosynthesis resume in a normal fashion, which is called escape from the Wolff-Chaikoff effect. This phenomenon is produced by lower iodide uptake during the escape from the acute Wolff–Chaikoff effect. It results from a decrease in Na+/I– symporter (NIS) expression. Exist abnormal autoregulation of the iodine in the autoimmune thyroid disease. The iodine organification persists and can result in or exacerbate hypothyroidism in patients with Hashimoto thyroiditis, or ameliorate hyperthyroidism in Graves disease. Thus, patients with Graves hyperthyroidism are more sensitive than normal subjects to the inhibitory effect of pharmacologic doses of iodine, making iodine treatment effective in some patients. Also, pharmacologic amounts of iodine may acutely ameliorate hyperthyroidism by blocking thyroid hormone release. Furthermore, it is used in preparation for thyroidectomy because it decreases the vascularity of the thyroid gland. Therefore, this decreases the risk of post-thyroidectomy hemorrhaging. KI should be administered at least one hour after the administration of thioamides to prevent new hormone synthesis since the new iodine substrate.
In the event of a nuclear accident, taken once daily, KI can decrease the mortality and morbidity of thyroid cancers provoked by radioactive iodine exposure; this is because it directly blocks the radioiodine uptake in the thyroid gland. KI floods the thyroid with non-radioactive iodine, preventing the uptake of the radioactive molecules, which subsequently get excreted in the urine.
The precise mechanism by which KI acts against inflammatory dermatoses is unknown. The dermatoses treatable with KI usually display neutrophils in the early stages. Research demonstrates that iodine, as well as dapsone, can suppress the production of toxic oxygen intermediates by polymorphonuclear cells and thus exert its anti-inflammatory effect. The precise mechanism by which KI kills fungi is also unknown. It is unclear whether KI works against fungi by a fungicidal mechanism or by enhancing the body's immunologic and nonimmunologic defense mechanisms. However, it is possible to assume that it has an important anti-inflammatory role, since the patients that show better response also present systemic symptoms and increased C-reactive protein. It usually improves fast, with fever, pain and erythema reduction in two days and complete remission in up to two weeks.
The dose of KI used to treat dermatoses is much higher than that in thyrotoxicosis (250 mg 3 times daily) or in radiation (100 to 150 mg single dose). Physicians typically begin treatment of inflammatory dermatoses with an oral dosage of 300 mg (approximately six drops of supersaturated potassium iodide (SSKI)) 3 times daily, followed by weekly increases as tolerated. In the case of mycoses, the administration is often higher, beginning at 600 mg (approximately 12 drops of SSKI) orally three times each day and often increased to 6 g (about 127 drops of SSKI) daily if tolerated.
Most presentations are given orally, usually with juice or milk, to protect against gastrointestinal irritation. However, there are some exceptions. There are several FDA-approved KI products, including tablets (65 and 130 mg) and oral solutions (65 mg/mL).
Additionally, there exist another two liquid presentations prescribed orally:
Adverse effects are unlikely when KI is used at low doses and for a short time (less than two weeks). The most common side effects are on the digestive system, predominantly being gastrointestinal intolerance and its bitter (metallic) taste; thus, the recommendation is that it be taken with juice or milk to protect against gastrointestinal irritation. However, there may occur significant side effects when high doses are administered, especially for the treatment of infectious skin disorders.
The acute side effects include diarrhea, nausea, vomiting, and stomach pain that can be ameliorated with gastrointestinal protection, and by avoiding rapid dosage increases. Nevertheless, prolonged use can cause Iodism or potassium toxicity. Iodism is an iodide poisoning syndrome characterized by soreness of the teeth and gums, severe headache, conjunctival hyperemia, lacrimation, blurred vision, rhinorrhea, and sialorrhea. Concurrent use of KI with impaired renal function or other potassium-containing medications, potassium-sparing diuretics, and angiotensin-converting enzyme inhibitors (ACE inhibitors) may result in hyperkalemia.
Because the patients receive large amounts of iodine in the drug, it could affect the metabolism of the thyroid gland. It can produce a WCE and produce hypothyroidism. However, there are autoregulation mechanisms that help maintain the normal function of the gland in euthyroid patients. The imbalance of thyroid hormones occurs when autoregulation is defective or absent. If it is just defective, the resulting WCE is inevitable, TSH increases, and hypothyroidism and goiter ensue. Failure to escape this condition, with resulting hypothyroidism, can result from with the administration of KI in patients with Hashimoto's thyroiditis, euthyroid patients previously treated by thyroid surgery or radioactive iodine for Graves' disease, patients taking certain drugs that inhibit thyroid function (e.g., lithium, phenazone, and, possibly, sulfonamides), patients previously treated with interferon alfa for chronic viral hepatitis, and patients with a history of amiodarone-induced thyrotoxicosis, subacute thyroiditis, or Graves disease. When autoregulation is absent, Jod-Basedow disease occurs. The absence of autoregulation is typically only seen in areas where iodine deficiency with long-standing goiters occur. This alteration produces an excess of thyroid hormone resulting in thyrotoxicosis.
Allergic reactions such as angioedema and urticaria should be a consideration during the administration of KI, like any drug. The use of KI can also cause an uncommon lesion in the skin called Ioderma, which is characterized by a severe acneiform, vesicular pustular, hemorrhagic, or urticarial lesions. Other systemic side effects of SSKI include urticaria, fever, eosinophilia, jaundice, pruritus, angioedema, and bronchospasm. In this case, the treatment is high-dose corticosteroid therapy.
KI is contraindicated in patients who have thyroid disease or are using any drug that could alter the thyroid function. Contraindications also include patients with an allergy to iodine. Clinicians should avoid giving it to patients with chronic renal failure because of the presence of potassium. Furthermore, it should be avoided in patients using potassium-sparing diuretics or angiotensin-converting-enzyme inhibitors to prevent hyperkalemia. Immunocompromised patients such as patients with cancer, cirrhosis, AIDS, and autoimmune diseases, or poorly managed diabetics, transplant patients, and those using corticosteroids should not use KI because it affects the immune system. It should not be indicated in pregnant or nursing women because it causes neonatal hypothyroidism, thyromegaly, fetal airway obstruction, and prolonged labor. Also, it is a pregnancy category D drug.
For all who prescribe KI, previous knowledge of the WCE, of the patients’ potassium levels, and their renal function is imperative. Recommendations include inquiring about any history of thyroid disease, autoimmune disease, or drugs that the patient is using. Unless there is a suspicion of thyroid disease, the baseline thyroid function test is not indicated. If KI use is for more than one month, it is recommended to do a screening test of TSH to ensure that the patients are not in hypothyroidism. If iodide-induced hypothyroidism is detected, these changes are reversible by discontinuing the administration of KI. Furthermore, according to the guidance of the FDA, thyroid function should be monitored in pregnant or breastfeeding women, neonates, and young infants if repeat doses are necessary following radioactive iodine exposure. The FDA strongly recommends monitoring neonates and infants for potential hypothyroidism, particularly when:
If iodide-induced hypothyroidism is detected, these changes are reversible by discontinuing the administration of KI. In a study of 7 patients with iodide-induced hypothyroidism, serum T4, T3, and TSH concentrations returned to normal within one month of iodide withdrawal.
The drug-induced-hyperkalemia is a medical urgency of which the physician should be aware. Prompt management is necessary with immediate (under 3 minutes) treatment: ECG monitoring is advisable. Changes suggest a potassium level greater than 7 mmol/L. Therefore, calcium gluconate administration is the recommended intervention in that case. Within minutes (under 30 minutes), the treatment is the combination of insulin-dextrose and beta-2 receptor agonists. Within hours (subacute) the management is sodium bicarbonate if the patient has acidosis, loop diuretics, and/or dialysis in patients with advanced Stage 5 kidney disease (eGFR less than 15 mL/min/1.73 m^2) or patients with very high potassium values (i.e., greater than 6.0 mmol/L).
In the case of iodism or ioderma, it is treatable with withdrawal and high doses of corticosteroids.
Physicians, nurses, and pharmacists in many parts of the world continue to use KI drug because of its effectiveness, and low cost or they can use it as a second-line drug when the first-line agent fails, is contraindicated, or cause intolerable side effects or severe allergic reaction to other medications. It is imperative to know the side effect of KI, particularly when treating dermatoses for extended periods, which requires monitoring the patient to prevent adverse effects, especially those related to thyroid disease. Furthermore, it is imperative to know the implication that this drug has in the prevention of exposure to radiation since clinicians have a brief window in which to apply it to patients and prevent thyroid cancer. Additionally, it is the public health’s responsibility to be aware of there capacity to store and administrate KI on time in the case of a nuclear emergency.
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