Potassium iodide is an antithyroid agent,162 antisporotrichotic agent,162 and expectorant.137, 162
Oral potassium iodide is used in the preoperative management of hyperthyroidism in patients with Graves' disease undergoing thyroidectomy†, usually as an adjunct to other antithyroid agents (e.g., methimazole, propylthiouracil) and/or β-adrenergic blocking agents (e.g., propranolol).151, 152, 154, 160, 161, 162, 165, 171 The American Thyroid Association (ATA), American Association of Clinical Endocrinologists (AACE), and others recommend that patients with Graves' disease scheduled for thyroidectomy be rendered euthyroid using other antithyroid agents (preferably methimazole) and then receive oral potassium iodide for 7-14 days (usually 10 days) in the immediate preoperative period.152, 160, 161, 165 In exceptional circumstances when the euthyroid state cannot be achieved prior to thyroidectomy (e.g., urgent need for surgery, allergy to antithyroid drugs), these experts recommend that oral potassium iodide and a β-adrenergic blocking agent (e.g., propranolol) be administered in the immediate preoperative period.160 Preoperative potassium iodide has traditionally been used in Graves' disease patients undergoing surgery in an attempt to decrease thyroid blood flow, vascularity, and intraoperative blood loss;151, 160, 162, 165, 171 however, the necessity and benefits of this strategy have been questioned.161, 162, 182, 183 Because of the risk of exacerbating hyperthyroidism, preoperative potassium iodide is not indicated in patients with toxic multinodular goiter or toxic adenoma undergoing thyroidectomy.160
Oral potassium iodide also is used in the management of severe, life-threatening thyrotoxicosis† (thyroid storm, thyrotoxicosis crisis) in conjunction with other antithyroid agents (e.g., methimazole, propylthiouracil), β-adrenergic blocking agents (e.g., propranolol), corticosteroids (hydrocortisone, dexamethasone), treatment of hyperpyrexia, and appropriate fluid, electrolyte, and respiratory support.154, 160, 161, 162, 165 Other antithyroid agents (e.g., methimazole, propylthiouracil) are initiated first to block thyroid hormone synthesis and conversion of tetraiodothyronine (thyroxine, T4) to triiodothyronine (T3); potassium iodide is initiated 1 hour after the other antithyroid agents and is used to block new hormone synthesis and thyroid hormone release.160
Oral potassium iodide is used during a radiation emergency to block thyroidal uptake of radioactive isotopes of iodine (e.g., I 131) that may be released into the environment (e.g., from a nuclear power plant) and thus minimize the risk of radiation-induced thyroid neoplasms related to internal exposures to radioiodines (inhaled or ingested).100, 101, 105, 138, 139, 141, 144, 145, 149, 150, 153, 155, 156, 164, 166, 167, 174 Although potassium iodide provides protection for the thyroid from radioiodines, the drug has no impact on body uptake of other radioactive materials and does not provide protection against external irradiation of any kind. 138
The extent of protection that oral potassium iodide can provide against inhaled or ingested radioiodines depends on several factors, including how quickly the drug is initiated and the total dose of radioactivity involved in the exposure.166 Thyroidal uptake of radioiodine can be reduced by more than 90-99% by oral intake of 130 mg of potassium iodide daily initiated shortly before or within 1-2 hours after acute exposure.100, 101, 105, 174 Potassium iodide may still provide substantial protection if taken 3-4 hours after exposure;138 however, although some data indicate that the drug may be about 40% effective if taken 8 hours after exposure,149, 173 it may offer little protection if taken 12 hours or more after exposure.149 The thyroid-blocking effect of a single 130-mg dose of potassium iodide persists for about 24 hours.138, 156, 166, 174 If the exposure lasts longer than 24 hours and involves continuing or ongoing contamination, additional doses may be necessary until the risk of significant exposure to radioiodines no longer exists.138, 174
The US Food and Drug Administration (FDA) issued updated recommendations in December 2001 on the use of potassium iodide in the event of a radiation emergency involving the release of radioactive iodine.138 These recommendations provide guidance to other federal agencies, including the Environmental Protection Agency (EPA) and Nuclear Regulatory Commission (NRC), and to state and local governments on safe and effective dosages of potassium iodide as an adjunct to other protective measures (e.g., evacuation, sheltering, assurance of uncontaminated milk and food).138 FDA recommendations issued in 1978 and 1982 were based on studies that estimated external thyroid exposure to radiation resulting from nuclear detonations in Hiroshima and Nagasaki and analogous studies in children who received therapeutic radiation to the head and neck.138 The 2001 recommendations were derived from much more comprehensive and reliable data relating internal radioiodine exposure (e.g., through inhalation or ingestion) to thyroid cancer risk following the 1986 Chernobyl nuclear reactor accident.138 Data from the Chernobyl incident indicated that the risk of thyroid cancer following a radiation emergency (e.g., nuclear reactor accident) is inversely related to age and that exposure to relatively small doses of radioiodine may lead to dramatic increases in thyroid cancer among exposed children.138 The revised FDA guidelines therefore recommend potassium iodide prophylaxis at predicted radiation exposures that are lower than previously recommended (particularly for children) and, to reduce the risk of hypothyroidism, lower dosage of potassium iodide for neonates, infants, and children compared with previous FDA recommendations.138 In addition, FDA no longer recommends emergency use of potassium iodide in adults over 40 years of age, unless a large internal radiation dose (e.g., at least 500 centigrays [cGy]) is anticipated.138 Potassium iodide is used as an adjunct to other protective measures (e.g., evacuation, sheltering, assurance of uncontaminated milk and food).138, 139, 145, 150, 153, 155, 162, 164, 167 The FDA recommends that individuals who are intolerant of potassium iodide and those for whom repeat doses of the drug are a concern (e.g., neonates 1 month of age or younger, pregnant or lactating women) be given priority with regard to these other protective measures.138
If a radiation emergency related to a US nuclear power plant occurs, decisions to recommend use of protective measures for public health and safety (including use of potassium iodide for thyroidal blockade) reside with state and/or local government authorities responsible for radiological emergency planning and response.101, 138, 139, 145, 150, 153, 155, 164, 166, 167 These authorities should inform the public of the nature of the radiation hazard and potential benefits and adverse effects of potassium iodide.138 For use in radiation emergencies, potassium iodide is commercially available in appropriate dosage forms (see Radiation Emergency under Dosage and Administration: Dosage)150, 153, 155, 164 and may also be retained in state or local stockpiles.139, 145, 167
Exposure to Radiopharmaceuticals
Oral potassium iodide is used for protection of the thyroid during diagnostic or therapeutic use of radiopharmaceuticals or drugs that have radioactive components† (e.g., iodine I 131 tositumomab; no longer commercially available in the US).162, 180, 181 Potassium iodide treatment is initiated prior to use of the radiolabeled diagnostic or therapeutic agent to saturate the thyroid and protect it from uptake of radioiodide and is continued until the estimated activity of the radiolabeled agent has decreased to acceptable levels after the procedure or treatment has been completed.162, 180, 181 In some cases, oral potassium iodide has been used in conjunction with other thyroid protective agents (e.g., methimazole, thyroxine).181
Oral potassium iodide is used for the treatment of cutaneous sporotrichosis† (localized to skin; also known as fixed cutaneous sporotrichosis) and lymphocutaneous sporotrichosis† (involves skin, subcutaneous tissues, regional lymphatics) caused by Sporothrix schenckii .108, 112, 118, 120, 121, 124, 143, 146, 168, 169, 172, 177, 178 Since it is inexpensive and generally has been effective,124, 143, 146, 124, 172, 177, 178 potassium iodide (oral solution containing 1 g/mL; also known as saturated solution of potassium iodide [SSKI®]) has historically been considered a standard of care for the treatment of cutaneous and lymphocutaneous sporotrichosis and continues to be a drug of first choice for these infections in some resource-limited settings and countries where the disease is endemic.143, 146, 169, 172, 176 However, compliance with the long-term treatment regimen can be a problem since the drug is associated with a substantial number of adverse effects (e.g., nausea, rash, fever, bitter or metallic taste, salivary gland enlargement, risk of iodism or potassium toxicity with prolonged use).124, 143, 146, 169 In addition, safety and efficacy of oral potassium iodide for the treatment of cutaneous or lymphocutaneous sporotrichosis have not been established in randomized, controlled clinical studies and efficacy of the drug compared with that of other antifungals used for the treatment of these infections (e.g., itraconazole, terbinafine, fluconazole) has not been established.176
The Infectious Diseases Society of America (IDSA) and other experts state that oral itraconazole is the drug of choice for the treatment of cutaneous and lymphocutaneous sporotrichosis and oral terbinafine and potassium iodide (oral solution containing 1 g/mL; also known as saturated solution of potassium iodide [SSKI®]) are the preferred alternatives.168, 169 For the treatment of cutaneous sporotrichosis, local hyperthermia (i.e., direct application of heat using a pocket warmer, infrared or far-infrared heater, or similar device that warms tissue to 42-43°C) is another alternative that can be used when antifungal agents or potassium iodide cannot be used (e.g., pregnant or nursing women).169
Oral potassium iodide is not effective for and should not be used for the treatment of extracutaneous sporotrichosis† (osteoarticular, pulmonary, meningeal) or disseminated sporotrichosis†.124, 168, 169 IV amphotericin B and oral itraconazole are the drugs of choice for these forms of sporotrichosis.124, 168, 169
Oral potassium iodide (oral solution containing 1 g/mL; also known as saturated solution of potassium iodide [SSKI®]) has been used as an expectorant in the symptomatic management of chronic pulmonary diseases where tenacious mucus complicates the condition (e.g., bronchial asthma, bronchitis, pulmonary emphysema);137 however, the drug has generally been replaced by more effective and safer expectorants. Although there is limited evidence that saline expectorants like potassium iodide can increase respiratory tract secretions, possibly as a reflex response to drug-induced gastric irritation, such evidence is sparse and inconclusive. In addition, there currently is insufficient evidence from well-designed studies to support the efficacy of potassium iodide as an expectorant.
Potassium iodide is administered orally.137, 150, 153, 154, 155, 164
For use during a radiation emergency, potassium iodide is commercially available as tablets containing 65 or 130 mg of the drug150, 153, 164 and as an oral solution containing 65 mg/mL.155 If the oral solution containing 65 mg/mL is used, the dose should be administered undiluted using the calibrated dropper provided by the manufacturer.155
For other indications, an oral solution of potassium iodide containing 1 g/mL (also known as saturated solution of potassium iodide [SSKI®]) also is available.137 If this oral solution is used, the dose should be administered in a glassful of water, fruit juice, or milk.137 To minimize GI irritation, the dose should be taken with food or milk.137 A calibrated dropper marked to deliver 300 mg (0.3 mL) or 600 mg (0.6 mL) of the drug is provided by the manufacturer.137 If a dose of the oral solution containing 1 g/mL is administered using a standard medicinal dropper, each drop (0.05 mL) contains 50 mg of potassium iodide.160, 163
Potassium iodide may be available as strong iodine solution (also known as Lugol's solution), an oral solution containing 50 mg of iodine and 100 mg of potassium iodide per mL; this preparation may be commercially available but is not approved by the US Food and Drug Administration (FDA).154 Doses of strong iodine solution should be diluted in water or juice.154 If a dose of strong iodine solution is administered using a standard medicinal dropper, each drop contains 8 mg of iodide.160
For use during a radiation emergency in infants, small children, and others who cannot swallow tablets, oral solutions (liquid mixtures) of potassium iodide can be prepared extemporaneously using 65- or 130-mg tablets of the drug.140, 150, 164
To prepare an oral solution containing 8.125 mg/5 mL (8.125 mg/teaspoon), the manufacturers state that a single 65-mg tablet of potassium iodide should be pulverized in a small bowl using the back of a teaspoon; 4 teaspoons (20 mL) of water should then be added to the bowl and mixed until the tablet dissolves.150, 164 This potassium iodide mixture should then be added to 4 teaspoons (20 mL) of milk (low-fat white or chocolate), orange juice, flat soda, raspberry syrup, or infant formula.150, 164
To prepare an oral solution containing 16.25 mg/5 mL (16.25 mg/teaspoon), the manufacturers state that a single 130-mg tablet of potassium iodide should be pulverized in a small bowl using the back of a teaspoon; 4 teaspoons (20 mL) of water should then be added to the bowl and mixed until the tablet dissolves.153 This potassium iodide mixture should then be added to 4 teaspoons (20 mL) of milk (low-fat white or chocolate), orange juice, flat soda, raspberry syrup, or infant formula.153
Alternatively, the FDA states that an oral solution containing 16.25 mg/5 mL (16.25 mg/teaspoon) can be prepared by putting two 65-mg tablets or one 130-mg tablet in a small bowl and adding 4 teaspoons (20 mL) of water to the bowl.140 After soaking in the water for 1 minute, the tablet(s) should be crushed using the back of the teaspoon until no large pieces remain.140 This potassium iodide mixture should then be added to 4 teaspoons (20 mL) of milk (white or chocolate), orange juice, soda (e.g., cola), infant formula, raspberry syrup, or water.140
These extemporaneous oral solutions of potassium iodide should be stored in a refrigerator and used within 7 days.140, 150, 153, 164
When oral potassium iodide is used in the preoperative management of hyperthyroidism in patients with Graves' disease undergoing thyroidectomy†, the drug is administered for 7-14 days (usually 10 days) in the immediate preoperative period (see Uses: Hyperthyroidism).152, 160, 161, 165 If the potassium iodide oral solution containing 1 g/mL (also known as saturated solution of potassium iodide [SSKI®]) is used, the recommended dosage is 50-100 mg (1-2 drops or 0.05-0.1 mL) 3 times daily in adults or 150-350 mg (3-7 drops or 0.15-0.35 mL) 3 times daily in children.160 Alternatively, if strong iodine solution (also known as Lugol's solution; commercially available but not FDA approved) is used, the recommended dosage in adults is 5-7 drops (0.25-0.35 mL) 3 times daily.160
When oral potassium iodide is used in the management of severe, life-threatening thyrotoxicosis† (thyroid storm, thyrotoxicosis crisis), the drug is initiated 1 hour after the initial dose of other antithyroid agents (see Uses: Hyperthyroidism).160 If the potassium iodide oral solution containing 1 g/mL (also known as saturated solution of potassium iodide [SSKI®]) is used, the recommended adult dosage is 250 mg (5 drops or 0.25 mL) every 6 hours.160 For the treatment of thyrotoxicosis in children, some experts recommend that the oral solution containing 1 g/mL (also known as saturated solution of potassium iodide [SSKI®]) be administered in a dosage of 50-250 mg (1-5 drops or 0.05-0.25 mL) 3 times daily.163
The dosage and duration of potassium iodide recommended during a radiation emergency and potential internal (inhalation or ingestion) exposure to radioiodines is based on predicted thyroid exposure, age and/or weight, and pregnancy and lactation status.138, 150, 153, 155, 156, 164
For use during a radiation emergency, potassium iodide is available as 65- or 130-mg tablets or as a solution containing 65 mg/mL.150, 153, 155, 164 If necessary in an emergency situation for an infant, small child, or other individual who cannot swallow tablets, the manufacturers and FDA have provided instructions on how to prepare extemporaneous oral solutions (liquid mixtures) using potassium iodide tablets.140, 150, 153, 164 (See Extemporaneous Oral Solutions under Dosage and Administration: Administration.)
For optimal protection against inhaled radioiodines, oral potassium iodide should be administered before or immediately coincident with passage of a radioactive cloud; potassium iodide may still have a substantial protective effect if administered 3-4 hours after exposure.138, 174 The protective effect of potassium iodide persists for about 24 hours.138, 156, 166, 174
Potassium iodide should be administered once daily until a risk of substantial exposure to inhaled or ingested radioiodines no longer exists.138, 150, 153, 155, 156, 164, 166 However, to minimize the risk of hypothyroidism during a period of critical brain development, repeat administration of potassium iodide should be avoided in neonates 1 month of age or younger, unless other protective measures are not available.138, 150, 153, 155, 156, 164, 166 (See Cautions: Pediatric Precautions.) In addition, repeat administration of the drug should be avoided in pregnant and lactating women, unless other protective measures are not available.138, 150, 153, 155, 164, 166 (See Cautions: Pregnancy and Lactation.)
The recommended adult dosage of oral potassium iodide for a radiation emergency is 130 mg once daily (one 130-mg tablet or two 65-mg tablets once daily).138, 150, 153, 156, 164 If the commercially available oral solution containing 65 mg/mL is used, adults should receive 130 mg once daily (2 mL once daily).155 Alternatively, if an extemporaneous oral solution containing 16.25 mg/5 mL (16.25 mg/teaspoon) is used, adults should receive a dosage of 130 mg once daily (40 mL or 8 teaspoons once daily).140
During a radiation emergency, the FDA recommends use of potassium iodide in adults 19 through 40 years of age if predicted thyroid exposure is 10 centigrays (cGy) or more and in pregnant or lactating women if predicted thyroid exposure is 5 cGy or more.138 Because of the risk of hypothyroidism, the FDA recommends potassium iodide in adults older than 40 years of age only if predicted thyroid exposure is 500 cGy or more.138
For a radiation emergency, adolescents older than 12 through 18 years of age should receive oral potassium iodide in a dosage of 130 mg once daily if they weigh 70 kg (150 lbs) or more or a dosage of 65 mg once daily if they weigh less than 70 kg (150 lbs).138, 140, 150, 153, 155, 156, 164 (See Table 1 and Table 2.) The FDA recommends use of potassium iodide in adolescents if predicted thyroid exposure is 5 cGy or more.138
For a radiation emergency, neonates and children through 12 years of age should receive potassium iodide in a dosage based on age.138, 150, 153, 155, 156, 164 (See Table 1 and Table 2.) The FDA recommends use of potassium iodide in neonates and children 12 years of age or younger if predicted thyroid exposure is 5 cGy or more.138
Age and Weight | Potassium Iodide Tablets (Iosat®, ThyroSafe®) | Potassium Iodide Oral Solution Containing 65 mg/mL (Thyroshield®) |
|---|---|---|
Birth to 1 month | 16.25 mg once daily (0.25 mL) | |
>1 month to 3 years | 32.5 mg once daily (0.5 mL) | |
>3 through 12 years | 65 mg once daily (one 65-mg tablet or ½ of 130-mg tablet) | 65 mg once daily (1 mL) |
>12 through 18 years weighing <70 kg (150 lbs) | 65 mg once daily (one 65-mg tablet or ½ of 130-mg tablet) | 65 mg once daily (1 mL) |
>12 through 18 years weighing ≥70 kg (150 lbs) | 130 mg once daily (two 65-mg tablets or one 130-mg tablet) | 130 mg once daily (2 mL) |
Age and Weight | Extemporaneous Oral Solution Containing 8.125 mg/5 mL (8.125 mg/teaspoon) | Extemporaneous Oral Solution Containing 16.25 mg/5 mL (16.25 mg/teaspoon) |
|---|---|---|
Birth to 1 month | 16.25 mg once daily (10 mL or 2 teaspoons) | 16.25 mg once daily (5 mL or 1 teaspoon) |
>1 month to 3 years | 32.5 mg once daily (20 mL or 4 teaspoons) | 32.5 mg once daily (10 mL or 2 teaspoons) |
>3 through 12 years | 65 mg once daily (40 mL or 8 teaspoons) | 65 mg once daily (20 mL or 4 teaspoons) |
>12 through 18 years weighing <70 kg (150 lbs) | 65 mg once daily (40 mL or 8 teaspoons) | 65 mg once daily (20 mL or 4 teaspoons) |
>12 through 18 years weighing ≥70 kg (150 lbs) | Use alternative preparation | 130 mg once daily (40 mL or 8 teaspoons) |
For the treatment of cutaneous or lymphocutaneous sporotrichosis† caused by Sporothrix schenckii , the Infectious Diseases Society of America (IDSA) and other clinicians state that the usual initial dosage of potassium iodide oral solution containing 1 g/mL (also known as saturated solution of potassium iodide [SSKI®]) in adults is 250 mg (5 drops or 0.25 mL) 3 times daily;169, 172 dosage may then be increased gradually as tolerated to a maximum of 2-2.5 g (40-50 drops or 2-2.5 mL) 3 times daily.124, 169 For the treatment of cutaneous or lymphocutaneous sporotrichosis in children, some experts recommend that the oral solution containing 1 g/mL (also known as saturated solution of potassium iodide [SSKI®]) be given in an initial dosage of 50 mg (1 drop or 0.05 mL) 3 times daily; dosage may then be increased gradually as tolerated.169, 172 The IDSA states that the maximum pediatric dosage of the oral solution containing 1 g/mL is 1 drop/kg 3 times daily or 2-2.5 g (40-50 drops or 2-2.5 mL) 3 times daily, whichever is lowest.169
The usual duration of oral potassium iodide therapy for the treatment of cutaneous or lymphocutaneous sporotrichosis† is 3-6 months.124, 172 The IDSA recommends that potassium iodide be continued for 2-4 weeks after cutaneous lesions resolve;169 other experts recommend that the drug be continued for 4-6 weeks after cutaneous lesions resolve.163
If the potassium iodide oral solution containing 1 g/mL (also known as saturated solution of potassium iodide [SSKI®]) is used as an expectorant, the usual adult dosage is 300 or 600 mg (0.3 or 0.6 mL) 3 or 4 times daily.137
Hypersensitivity reactions to iodides may occur and may be manifested by angioedema, cutaneous and mucosal hemorrhage, and signs and symptoms resembling serum sickness, such as fever, arthralgia, lymph node enlargement, and eosinophilia.137, 162 Urticaria, thrombotic thrombocytopenic purpura, and fatal periarteritis have also been attributed to iodide hypersensitivity. Hypocomplementemic vasculitis in some patients with chronic urticaria or systemic lupus erythematosus has been associated with iodide sensitivity, and some clinicians caution that potassium iodide may precipitate severe systemic illness in such patients. Jodbasedow or iodine-induced thyrotoxicosis may occur with low doses of iodides (i.e., less than 25 mg of iodine daily); this effect is uncommon in the US but more frequent in areas with endemic iodine deficiency.100
Manifestations of iodism (chronic iodine poisoning) may occur when potassium iodide is given in large doses or over extended periods of time.137, 154, 162 Iodism is usually manifested as a metallic taste, burning in the mouth and throat, soreness of the teeth and gums, increased salivation, coryza, sneezing, and irritation of the eyes with swelling of the eyelids.137, 162, 170 Severe headache, productive cough, pulmonary edema, dyspnea, bronchospasm, and swelling and tenderness of the parotid and submaxillary glands may occur.162 The throat, pharynx, larynx, and tonsils may become inflamed.162 Mild acneiform eruptions may occur, usually in seborrheic areas; rarely, severe and sometimes fatal eruptions (ioderma) may occur.137, 162 Gastric irritation is common and diarrhea, sometimes bloody, may also occur.137, 154, 162, 170 Signs and symptoms of iodism generally subside spontaneously within a few days of discontinuing the drug; symptomatic and supportive therapy, including abundant fluid and salt intake to help eliminate iodide, may be necessary.137
Prolonged use of iodides or excessive doses may result in thyroid gland hyperplasia, thyroid adenoma, goiter, and severe hypothyroidism.138, 151, 152, 162 Prolonged use of iodides may also induce hyperthyroidism,162 particularly in older individuals, patients with preexisting nontoxic nodular goiter, and patients residing in areas with endemic iodine deficiency.138
Precautions and Contraindications
Potassium iodide is contraindicated in individuals with known sensitivity to iodides or any ingredient in the formulation.137, 150, 153, 154, 155, 164
Potassium iodide also is contraindicated in patients with dermatitis herpetiformis, hypocomplementemic vasculitis, or nodular thyroid disease (e.g., multinodular goiter) with heart disease.150, 153, 155, 164
Since some individuals are markedly sensitive to iodides, initial potassium iodide doses should be administered with caution. Patients at risk for iodine-induced adverse effects (e.g., hyperthyroidism, thyrotoxicosis) include older patients162 and those with goiter or autoimmune thyroid disease.138, 156, 162, 166 Potassium iodide, especially when indicated for more than a few days, should be used with caution in patients with multinodular goiter, Graves' disease, or autoimmune thyroiditis.138, 156
In the event of a radiation emergency, potassium iodide should be used with caution and as directed by public authorities.138, 150, 153, 155, 156, 164 For radiation emergencies, potassium iodide may be used in patients with preexisting thyroid diseases if they do not have nodular thyroid conditions with heart disease; however, careful supervision by clinicians is recommended if therapy must be administered for more than a few days.150, 153, 155, 156, 164
Vesication and desquamation may occur if strong iodine solution (also known as Lugol's solution; commercially available but not approved by the US Food and Drug Administration [FDA]) is allowed to pool in contact with skin.154 If accidental contact of strong iodine solution with skin or eyes occurs, the skin or eyes should be flushed with copious amounts of water for 15 minutes.154
Safety and efficacy of potassium iodide oral solution containing 1 g/mL (also known as saturated solution of potassium iodide [SSKI®]) have not been established in children.137 Potassium iodide oral solution containing 1 g/mL has been used for the treatment of cutaneous and lymphocutaneous sporotrichosis in children†108, 118, 120, 172 and is recommended by the Infectious Disease Society of America (IDSA) as an alternative for the treatment of these infections in children.169 (See Uses: Sporotrichosis.)
Children are more susceptible to the dangerous effects of radioactive iodide than adults and the benefits of potassium iodide during a radiation emergency exceed the risks.140 However, to minimize the risk of hypothyroidism during a period of critical brain development, repeat administration of potassium iodide should be avoided in neonates 1 month of age or younger, unless other protective measures are not available.138, 150, 153, 155, 156, 164, 166 If potassium iodide is used in a neonate 1 month of age or younger, the neonate should be monitored for the potential development of hypothyroidism by measuring thyrotropin (thyroid-stimulating hormone, TSH) and, if indicated, free thyroxine (free T4) and thyroid replacement therapy should be instituted if hypothyroidism occurs.138, 150, 153, 155, 164
In a radiation emergency, children and neonates unable to tolerate potassium iodide and neonates in whom repeat administration of the drug is a concern should be given priority with regard to other protective measures (e.g., evacuation, sheltering, assurance of uncontaminated milk and food).138
Iodides readily cross the placenta137, 138, 157, 162 and may result in abnormal thyroid function and/or goiter in the neonate.137, 157, 160, 162 Fetal thyroid may be most susceptible to the effects of excess iodine at the end of gestation.160
Some experts state that potassium iodide is contraindicated in pregnant women.163 The American Academy of Pediatrics (AAP) states that use of potassium iodide as an expectorant is contraindicated during pregnancy.157
There is no evidence that short-term use (e.g., 10 days) of potassium iodide for preoperative management of hyperthyroidism in pregnant women with Graves' disease undergoing thyroidectomy† is harmful to the fetus.157, 160 If thyroidectomy is necessary for the treatment of hyperthyroidism during pregnancy, the American Thyroid Association (ATA) and American Association of Clinical Endocrinologists (AACE) recommend that the surgery be performed during the second trimester.160
The FDA recommends that pregnant women receive potassium iodide during a radiation emergency for their own protection and that of the fetus;138 however, repeat administration should be avoided during pregnancy, unless other protective measures are not available.138, 150, 153, 155, 156, 164, 166 When repeat administration is indicated in a pregnant woman, consultation with a clinician is recommended138, 150, 153, 155, 164 and thyroid function monitoring may be indicated in the neonate.138
If potassium iodide is used during pregnancy or if the patient becomes pregnant while receiving the drug, the patient should be informed of the potential risks to the fetus.137
Potassium iodide is distributed into milk137, 138, 149, 162 and may cause rash and thyroid suppression in nursing infants.137
The AAP considers potassium iodide to be compatible with breast-feeding.157
In a radiation emergency, the FDA recommends that lactating women receive potassium iodide for their own protection.138 However, repeat administration should be avoided in lactating women unless other protective measures are not available.138, 150, 153, 155, 164, 166 If repeat administration is indicated in a nursing woman, consultation with a clinician is recommended;138, 150, 153, 155, 164, 166 thyroid function monitoring may be indicated in a breast-fed neonate.138
Because radioactive iodine is distributed into milk, some experts (including the AAP) recommend that lactating women temporarily not breast-feed after a radiation emergency, unless no alternative is available.149 Breast-feeding can then be resumed when public authorities declare it safe to do so.149 The fact that administration of potassium iodide to lactating women potentially can reduce the radioiodine content of milk should be considered.138
Concomitant use of lithium salts and iodides may result in additive or synergistic hypothyroid effects.128, 129, 132, 133, 134, 135, 136, 137, 163 Hypothyroidism has been reported in several patients who received the drugs concomitantly.128, 131, 134, 135, 136, 163 A lithium salt and potassium iodide generally should not be used concomitantly; if the drugs are used together, the patient should be monitored closely for signs and symptoms of hypothyroidism.128, 129, 131, 135, 136
Concomitant use of antithyroid agents (e.g., methimazole) and potassium iodide may result in additive hypothyroid and goitrogenic effects.137, 170
Concomitant use of potassium iodide and potassium-containing drugs, potassium-sparing diuretics, or angiotensin-converting enzyme (ACE) inhibitors may be associated with hyperkalemia, which may result in cardiac arrhythmias or cardiac arrest.137
Thyroid Hormone Synthesis and Regulation
Iodine is an essential component of thyroid hormones, tetraiodothyronine (thyroxine, T4) and triiodothyronine (T3), comprising 65 and 59% of the weights, respectively.142 Thyroxine and triiodothyronine are produced in the thyroid gland by the iodination and coupling of the amino acid tyrosine. (See Chemistry in the Thyroid Agents General Statement.) Thyroid hormones and thus iodine are essential for human life.142 The hormones regulate many key biochemical reactions, especially protein synthesis and enzymatic activity, and target the developing brain, muscle, heart, pituitary, and kidneys.142
Iodine is ingested in a variety of chemical forms, but because its content in most food sources is low, iodine present in iodized salt or in processed foods from the addition of iodized salt or other additives (potassium iodate, calcium iodate, cuprous iodide) is its principal source in humans in developed countries.142 Iodine also is available in dietary supplements and from other sources (e.g., drugs such as thyroid agents [hormones] and amiodarone).142 Most ingested iodine is reduced in the GI tract and absorbed almost completely.142 Under normal conditions, the absorption of dietary iodine exceeds 90%.142 Once absorbed systemically, iodide is removed principally by the thyroid gland and kidneys.142 The thyroid gland selectively concentrates iodide in amounts required for adequate thyroid hormone synthesis, with most of the remaining iodide being excreted renally.142 Salivary glands, breast, choroid plexus, and gastric mucosa also can concentrate iodide; however, other than the lactating breast, these tissues are minor pathways of uncertain importance.142
A sodium/iodide transporter in the thyroidal basal membrane is responsible for iodine concentration in the gland, transferring iodide from systemic circulation into the thyroid gland at a concentration gradient of 20-50 times that of plasma to ensure that the gland receives adequate amounts of iodine for hormone synthesis.142 During iodine deficiency, the thyroid gland concentrates most of the iodine available from plasma.142 Iodide participates in a complex series of reactions in the thyroid gland to produce thyroid hormones.142 Thyroglobulin is synthesized in thyroid cells and serves as an iodination vehicle.142 Thyroperoxidase and hydrogen peroxide promote the oxidation of iodide and its attachment to tyrosyl residues within the thyroglobulin molecule to produce the hormone precursors diiodotyrosine and monoiodotyrosine.142 Thyroperoxidase further catalyzes intramolecular coupling of 2 molecules of diiodotyrosine to produce T4 and coupling of a molecule of diiodotyrosine and a molecule of monoiodotyrosine to produce T3.142 The average adult thyroid gland in individuals residing in an iodine-sufficient geographic region contains about 15 mg of iodine.142 Iodine is not released into systemic circulation but instead is stored principally in diiodo and monoiodo tyrosine precursors, removed from the tyrosine moiety by a specific deiodinase, and then recycled within the thyroid gland as a mechanism of iodine conservation.142
Once in systemic circulation, thyroxine and triiodothyronine attach to several binding proteins (e.g., thyronine-binding globulin, transthyretin, albumin), which then migrate to target tissues where thyroxine is deiodinated to triiodothyronine, the metabolically active form of thyroid hormone.142 The iodine that is removed from thyroxine returns to the serum iodine pool and follows the usual iodine cycle or is excreted renally.142 Thyrotropin (TSH) is the major thyroid function regulator.142 Thyrotropin affects several sites within thyrocytes, the principal actions of which are to increase thyroidal uptake of iodine and to break down thyroglobulin to release thyroid hormone into systemic circulation.142 An elevated serum thyrotropin concentration indicates primary hypothyroidism and a decreased serum concentration indicates hyperthyroidism.142
The normal thyroid gland takes up the amount of systemically circulating iodine necessary to make the necessary amount of thyroid hormone for the body's needs.142 In iodine deficiency, the thyroid gland will concentrate more radioactive iodine, and the gland will concentrate less in iodine excess.142 However, other factors can influence radioactive iodine uptake, including thyroidal overproduction of hormone (hyperthyroidism), hypothyroidism, subacute thyroiditis, and many chemical and medicinal products.142 When iodine equilibrium is present, the mean daily thyroid iodine accumulation and release are similar.142
In patients with hyperthyroidism, iodide rapidly inhibits the release of thyroid hormones via a direct effect on the thyroid gland and inhibits the synthesis of thyroid hormones. Iodide apparently attenuates the effects of thyrotropin that are mediated via cAMP. The vascularity of the thyroid gland is reduced, the gland becomes much firmer, the cells become smaller, colloid reaccumulates in the follicles, and the quantity of bound iodine increases. The effects of potassium iodide on thyroid function are usually observed within 24 hours and are maximal after 10-15 days of continuous therapy; however, the drug does not completely control the manifestations of hyperthyroidism, and after a variable period of time the salutary effects subside.
Effects in Radiation Emergencies
In the event of a radiation emergency, isotopes of iodine may be released into the environment.100, 141, 144 Radioactive iodine is taken up and stored in the thyroid gland in the same manner as stable iodine.100, 138, 141 (See Pharmacology: Thyroid Hormone Synthesis and Regulation.) The selective and rapid concentration and storage of radioactive iodine in the thyroid gland results in internal radiation exposure to the thyroid and increased risk of thyroid cancer and benign nodules and, at high doses, hypothyroidism.141 Administration of stable iodine (potassium iodide) before or promptly after intake of radioactive iodine blocks or reduces accumulation of radioactive iodine in the thyroid gland.100, 138, 141, 144
The mechanism of action of potassium iodide in the treatment of cutaneous or lymphocutaneous sporotrichosis† caused by Sporothrix schenckii has not been determined.143, 147, 162, 169 In vitro, potassium iodide does not appear to increase monocyte or neutrophil killing of S. schenckii .143, 147 However, exposure of the yeast form of S. schenckii to various concentrations of iodine (iodine and potassium iodide solution) in vitro has resulted in rapid cell destruction.143, 148
Effects on Respiratory Tract Secretions
Potassium iodide is thought to act as an expectorant by increasing respiratory tract secretions and thereby decreasing the viscosity of mucus;137 however, this remains to be clearly established.
Potassium iodide occurs as hexahedral crystals, either transparent and colorless or somewhat opaque and white, or as a white, granular powder. The drug is slightly hygroscopic. Potassium iodide is very soluble in water and soluble in alcohol. Each gram of potassium iodide contains about 6 mEq of potassium.
Potassium iodide is commercially available as tablets containing 65 or 130 mg of the drug150, 153, 164 and as an oral solution containing 65 mg/mL in a black raspberry-flavored solution.155 An aqueous oral solution of potassium iodide containing 1 g/mL also is commercially available; this preparation is known as saturated solution of potassium iodide (SSKI®).137
Potassium iodide may be available as strong iodine solution (also known as Lugol's solution), a solution containing 50 mg of iodine and 100 mg of potassium iodide per mL.154, 179 Strong iodine solutions may be commercially available for oral154 or topical administration,179 but these preparations are not approved by the US Food and Drug Administration (FDA).154, 179
Potassium iodide tablets should be stored at 20-25°C in their original foil pack and protected from moisture.150, 153, 164
Potassium iodide oral solution containing 65 mg/mL should be stored at 25°C, but may be exposed to 15-30°C; the solution should be stored in a tight container and protected from light.155
Potassium iodide oral solution containing 1 g/mL (also known as saturated solution of potassium iodide [SSKI®]) should be stored at 15-30°C in a tight container and protected from light.137 The oral solution may crystallize if exposed to cold temperatures; however, crystals will dissolve if the solution is warmed and shaken.137 The solution should be discarded if it turns brownish-yellow in color.137
Oral solutions of potassium iodide prepared extemporaneously using 65- or 130-mg tablets (see Extemporaneous Oral Solutions under Dosage and Administration: Administration) should be stored in the refrigerator and any unused solution discarded after 7 days.140, 150, 153, 164
Additional Information
The American Society of Health-System Pharmacists, Inc. represents that the information provided in the accompanying monograph was formulated with a reasonable standard of care, and in conformity with professional standards in the field. Readers are advised that decisions regarding use of drugs are complex medical decisions requiring the independent, informed decision of an appropriate health care professional, and that the information contained in the monograph is provided for informational purposes only. The manufacturer's labeling should be consulted for more detailed information. The American Society of Health-System Pharmacists, Inc. does not endorse or recommend the use of any drug. The information contained in the monograph is not a substitute for medical care.
Excipients in commercially available drug preparations may have clinically important effects in some individuals; consult specific product labeling for details.
Please refer to the ASHP Drug Shortages Resource Center for information on shortages of one or more of these preparations.
Routes | Dosage Forms | Strengths | Brand Names | Manufacturer |
|---|---|---|---|---|
Oral | Solution | Iodine 50 mg/mL and Potassium Iodide 100 mg/mL | Strong Iodine Solution | |
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