Potassium Iodide (Monograph)

Brand names: Iosat, SSKI, ThyroSafe, ThyroShield
Drug class: Antithyroid Agents
ATC class: R05CA02
VA class: RE302
CAS number: 7681-11-0

Medically reviewed by Drugs.com on May 19, 2023. Written by ASHP.

Introduction

Antithyroid agent, antisporotrichotic agent, and expectorant.

Uses for Potassium Iodide

Hyperthyroidism

Preoperative management of hyperthyroidism in patients with Graves’ disease undergoing thyroidectomy^{† [off-label]}. American Thyroid Association (ATA), American Association of Clinical Endocrinologists (AACE), and others recommend that patients with Graves’ disease scheduled for surgery be rendered euthyroid using other antithyroid agents (preferably methimazole) and then receive potassium iodide for 7–14 days (usually 10 days) in immediate preoperative period. In exceptional circumstances when euthyroid state cannot be achieved prior to thyroidectomy (e.g., urgent need for surgery, allergy to antithyroid drugs), these experts recommend use of potassium iodide and a β-adrenergic blocking agent (e.g., propranolol) in immediate preoperative period. Preoperative potassium iodide has traditionally been used in such patients to decrease thyroid blood flow, vascularity, and intraoperative blood loss; however, some clinicians question necessity and benefits of this strategy.

Management of severe, life-threatening thyrotoxicosis^{† [off-label]} (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. Initiate other antithyroid agents first to block thyroid hormone synthesis and conversion of tetraiodothyronine (thyroxine, T₄) to triiodothyronine (T₃); initiate potassium iodide 1 hour after the other agents to block new hormone synthesis and thyroid hormone release.

Radiation Emergency

Blockage of 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) to minimize the risk of radiation-induced thyroid neoplasms related to internal exposures to radioiodines (inhaled or ingested). Has no impact on uptake of other radioactive materials and does not provide protection against external irradiation of any kind.

Used as an adjunct to other protective measures (e.g., evacuation, sheltering, assurance of uncontaminated milk and food). Individuals unable to tolerate potassium iodide and individuals for whom repeat doses of the drug are a concern (e.g., neonates ≤1 month of age, pregnant or lactating women) should be given priority with regard to these other protective measures.

For use in radiation emergencies, potassium iodide is commercially available in appropriate dosage forms (see Dosage and Administration) and may also be retained in state or local stockpiles.

Decisions to recommend protective measures (including use of potassium iodide) in an emergency situation related to a US nuclear power plant reside with state and/or local government authorities responsible for radiological emergency planning and response. (See Advice to Patients.)

Exposure to Radiopharmaceuticals

Used to protect thyroid during diagnostic or therapeutic use of radiopharmaceuticals or drugs that have radioactive components^{† [off-label]} (e.g., iodine I 131 tositumomab; no longer commercially available in US).

Initiated prior to administration of radiolabeled diagnostic or therapeutic agent to saturate thyroid and protect it from uptake of radioiodide; continued until estimated activity of radiolabeled agent has decreased to acceptable levels after completion of the procedure or treatment.

Sporotrichosis

Treatment of cutaneous sporotrichosis^{† [off-label]} (localized to skin; also known as fixed cutaneous sporotrichosis) and lymphocutaneous sporotrichosis^{† [off-label]} (involves skin, subcutaneous tissues, regional lymphatics) caused by Sporothrix schenckii.

Because it is inexpensive and generally effective, potassium iodide (oral solution containing 1 g/mL; also known as saturated solution of potassium iodide [SSKI]) has historically been a standard of care for treatment of cutaneous and lymphocutaneous sporotrichosis and is a drug of first choice for these infections in some resource-limited settings and countries where the disease is endemic. However, safety and efficacy for treatment of these infections not established in controlled clinical trials.

IDSA and others recommend itraconazole as drug of choice for treatment of cutaneous and lymphocutaneous sporotrichosis; terbinafine and potassium iodide (oral solution containing 1 g/mL; also known as saturated solution of potassium iodide [SSKI]) are preferred alternatives. Local hyperthermia (i.e., direct application of heat using pocket warmer, infrared or far-infrared heater, or similar device that warms tissue to 42–43°C) is another alternative for treatment of cutaneous sporotrichosis when antifungals or potassium iodide cannot be used (e.g., pregnant or nursing women).

Not effective and should not be used for treatment of extracutaneous sporotrichosis^† (pulmonary, osteoarticular, meningeal) or disseminated sporotrichosis^†; IV amphotericin B and oral itraconazole are drugs of choice for these forms of sporotrichosis.

Cough

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). However, efficacy not established and the drug generally has been replaced by more effective and safer expectorants.

Potassium Iodide Dosage and Administration

Administration

Oral Administration

Administer orally.

Oral solution containing 65 mg/mL: Administer undiluted using calibrated dropper provided by manufacturer.

Oral solution containing 1 g/mL (also known as saturated solution of potassium iodide [SSKI]): Dilute dose in glassful of water, fruit juice, or milk. To minimize GI irritation, take dose with food or milk. Manufacturer provides calibrated dropper marked to deliver 300 mg (0.3 mL) or 600 mg (0.6 mL). If administered using standard medicinal dropper, each drop (0.05 mL) contains 50 mg of potassium iodide.

Strong iodine oral solution containing 50 mg of iodine and 100 mg of potassium iodide per mL (also known as Lugol’s solution; commercially available but not FDA approved): Dilute dose in water or juice. If administered using standard medicinal dropper, each drop contains 8 mg of iodide.

Extemporaneous Oral Solutions

For use during a radiation emergency in infants, small children, and others who cannot swallow tablets, oral solution (liquid mixture) containing 8.125 mg/5 mL (8.125 mg/teaspoon) or 16.25 mg/5 mL (16.25 mg/teaspoon) can be prepared extemporaneously using 65- or 130-mg tablets.

Extemporaneous oral solution containing 8.125 mg/5 mL (8.125 mg/teaspoon): Manufacturers state pulverize 65-mg tablet in small bowl using the back of a teaspoon; add 4 teaspoons (20 mL) of water and mix until dissolved; add this mixture to 4 teaspoons (20 mL) of milk (low-fat white or chocolate), orange juice, flat soda, raspberry syrup, or infant formula.

Extemporaneous oral solution containing 16.25 mg/5 mL (16.25 mg/teaspoon): Manufacturers state pulverize 130-mg tablet in small bowl using the back of a teaspoon; add 4 teaspoons (20 mL) of water and mix until dissolved; add this mixture to 4 teaspoons (20 mL) of milk (low-fat white or chocolate), orange juice, flat soda, raspberry syrup, or infant formula.

Alternatively, to prepare oral solution containing 16.25 mg/5 mL (16.25 mg/teaspoon), FDA states place two 65-mg tablets or one 130-mg tablet in small bowl; add 4 teaspoons (20 mL) of water and allow to soak for 1 minute; using the back of the teaspoon, crush tablet(s) in the water until there are no large pieces; add this mixture to 4 teaspoons (20 mL) of milk (white or chocolate), orange juice, soda (e.g., cola), infant formula, raspberry syrup, or water.

Store extemporaneous oral solutions in a refrigerator for up to 7 days.

Dosage

Pediatric Patients

Hyperthyroidism†

Preoperative Use in Patients with Graves’ Disease Undergoing Thyroidectomy†

Oral

Oral solution containing 1 g/mL (also known as saturated solution of potassium iodide [SSKI]): 150–350 mg (3–7 drops or 0.15–0.35 mL) 3 times daily for 10 days in immediate preoperative period.

Ideally, administer only after patient is euthyroid after treatment with other antithyroid agents. (See Hyperthyroidism under Uses.)

Thyroid Storm (Thyrotoxicosis Crisis)†

Oral

Oral solution containing 1 g/mL (also known as saturated solution of potassium iodide [SSKI]): 50–250 mg (1–5 drops or 0.05–0.25 mL) 3 times daily suggested by some clinicians.

Radiation Emergency

Oral

Recommended dosage and duration to provide protection during radiation emergency (inhalation or ingestion exposure) is based on predicted thyroid exposure, age, and weight (see Table 1 and Table 2).

For optimal protection, take before or immediately coincident with passage of a radioactive cloud or within 1–2 hours of exposure; administration 3–4 hours after exposure may still provide substantial protection.

Use for self-medication only when directed by public authorities. FDA recommends potassium iodide in infants, children, and adolescents when predicted thyroid exposure is ≥5 centigrays (cGy).

Single daily dose; do not take more often than once every 24 hours. Continue daily dose as directed by public authorities until risk of substantial exposure to radioiodines by inhalation or ingestion no longer exists.

Neonates ≤1 month of age: Avoid repeat administration. Consult clinician if more than a single dose indicated. (See Pediatric Use under Cautions.)

Sporotrichosis†

Cutaneous or Lymphocutaneous Sporotrichosis†

Oral

Oral solution containing 1 g/mL (also known as saturated solution of potassium iodide [SSKI]): Initially, 50 mg (1 drop or 0.05 mL) 3 times daily. Gradually increase dosage as tolerated to maximum of 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.

Usual treatment duration is 3–6 months. IDSA recommends continuing treatment for 2–4 weeks after cutaneous lesions resolve; others recommend continuing for 4–6 weeks after cutaneous lesions resolve.

Adults

Hyperthyroidism†

Preoperative Use in Patients with Graves’ Disease Undergoing Thyroidectomy†

Oral

Oral solution containing 1 g/mL (also known as saturated solution of potassium iodide [SSKI]): 50–100 mg (1–2 drops or 0.05–0.1 mL) 3 times daily for 10 days in immediate preoperative period.

Strong iodine solution (also known as Lugol’s solution; commercially available but not FDA approved): 5–7 drops or 0.25–0.35 mL 3 times daily for 10 days in immediate preoperative period.

Ideally, administer only after patient is euthyroid after treatment with other antithyroid agents. (See Hyperthyroidism under Uses.)

Thyroid Storm (Thyrotoxicosis Crisis)†

Oral

Oral solution containing 1 g/mL (also known as saturated solution of potassium iodide [SSKI]): 250 mg (5 drops or 0.25 mL) every 6 hours.

Initiate 1 hour after initial dose of other antithyroid agents. (See Hyperthyroidism under Uses).

Radiation Emergency

Oral

Recommended dosage and duration to provide protection during radiation emergency (inhalation or ingestion exposure) is based on predicted thyroid exposure, age, and pregnancy or lactation status.

For optimal protection, take before or immediately coincident with passage of a radioactive cloud or within 1–2 hours of exposure; administration 3–4 hours after exposure may still provide substantial protection.

Use for self-medication only when directed by public authorities. FDA recommends potassium iodide in adults 19 through 40 years of age when predicted thyroid exposure is ≥10 cGy and in pregnant or lactating women when predicted thyroid exposure is ≥5 cGy; because of risk of hypothyroidism, recommended in adults >40 years of age only when predicted thyroid exposure is ≥500 cGy.

Single daily dose; do not take more often than once every 24 hours. Continue daily dose as directed by public authorities until risk of substantial exposure to radioiodines by inhalation or ingestion no longer exists.

Tablets: 130 mg once daily (one 130-mg tablet or two 65- mg tablets once daily).

Oral solution containing 65 mg/mL: 130 mg once daily (2 mL once daily).

Extemporaneous oral solution containing 16.25 mg/5 mL (16.25 mg/teaspoon): 130 mg once daily (40 mL or 8 teaspoons once daily).

Pregnant and lactating women: Avoid repeat administration. Consult clinician if more than a single dose indicated. (See Pregnancy and See Lactation under Cautions.)

Sporotrichosis†

Cutaneous or Lymphocutaneous Sporotrichosis†

Oral

Oral solution containing 1 g/mL (also known as saturated solution of potassium iodide [SSKI]): Initially, 250 mg (5 drops or 0.25 mL) 3 times daily. Gradually increase dosage as tolerated to a maximum of 2–2.5 g (40–50 drops or 2–2.5 mL) 3 times daily.

Usual treatment duration is 3–6 months. IDSA recommends continuing treatment for 2–4 weeks after cutaneous lesions resolve; others recommend continuing for 4–6 weeks after cutaneous lesions resolve.

Cough

Oral

Oral solution containing 1 g/mL (also known as saturated solution of potassium iodide [SSKI]): 300 or 600 mg (0.3 or 0.6 mL) 3 or 4 times daily.

Prescribing Limits

Pediatric Patients

Radiation Emergency

Oral

Neonates ≤1 month of age: Maximum 1 dose without consulting clinician. (See Pediatric Use under Cautions.)

Pediatric patients >1 month through 18 years of age: Maximum 1 dose every 24 hours.

Sporotrichosis†

Cutaneous or Lymphocutaneous Sporotrichosis†

Oral

Oral solution containing 1 g/mL (also known as saturated solution of potassium iodide [SSKI]): Maximum 1 drop/kg or 2–2.5 g (40–50 drops or 2–2.5 mL) 3 times daily, whichever is lowest.

Adults

Radiation Emergency

Oral

Pregnant and lactating women: Maximum 1 dose without consulting clinician. (See Pregnancy and See Lactation under Cautions.)

Other adults ≥19 years of age: Maximum 1 dose every 24 hours.

Sporotrichosis†

Cutaneous or Lymphocutaneous Sporotrichosis†

Oral

Oral solution containing 1 g/mL (also known as saturated solution of potassium iodide [SSKI]): Maximum 2–2.5 g (40–50 drops or 2–2.5 mL) 3 times daily.

Cautions for Potassium Iodide

Contraindications

• Known sensitivity to iodides or any ingredient in the formulation.

• Dermatitis herpetiformis.

• Hypocomplementemic vasculitis.

• Nodular thyroid disease (e.g., multinodular goiter) with heart disease.

Warnings/Precautions

Warnings

Fetal/Neonatal Morbidity

May cause fetal harm (i.e., abnormal thyroid function, fetal goiter). (See Pregnancy under Cautions.)

Sensitivity Reactions

Hypersensitivity Reactions

Angioedema, cutaneous and mucosal hemorrhage, and signs and symptoms resembling serum sickness (e.g., fever, arthralgia, lymph node enlargement, eosinophilia) may occur. Urticaria, thrombotic thrombocytopenic purpura, and fatal periarteritis also reported.

Patients with hypocomplementemic vasculitis associated with chronic urticaria or systemic lupus erythematosus are at increased risk of adverse effects and severe systemic illness; do not use in such patients. (See Contraindications under Cautions.)

Patients with dermatitis herpetiformis are at increased risk of adverse effects; do not use in such patients. (See Contraindications under Cautions.)

If hypersensitivity reaction occurs (e.g., difficulty breathing/speaking/swallowing, shortness of breath, wheezing, swelling of mouth/tongue/throat/face/hands/feet, rash), discontinue the drug.

Major Toxicities

Iodism (Chronic Iodine Poisoning)

Iodism (chronic iodine poisoning) may occur with long-term therapy or high dosage. Manifestations include burning in mouth or throat, severe headache, metallic taste, soreness of teeth and gums, head cold symptoms, coryza, sneezing, eye irritation with eyelid swelling, unusual increase in salivation, acneiform lesions in seborrheic areas, and, rarely, severe skin eruptions (ioderma). Productive cough, pulmonary edema, dyspnea, bronchospasm, and swelling/tenderness of parotid and submaxillary glands, throat inflammation, gastric irritation, and diarrhea (sometimes bloody) also may occur.

If manifestations of iodism occur, discontinue potassium iodide and initiate appropriate supportive therapy. Symptoms usually resolve soon after drug discontinued; abundant fluid and salt intake may help eliminate iodide.

General Precautions

Alterations in Thyroid Function

Long-term use or high dosage may induce hyperthyroidism, particularly in older individuals, patients with preexisting nontoxic nodular goiter, and patients residing in areas with endemic iodine deficiency. Symptoms of hyperthyroidism may include irregular heartbeat and chest pain.

In some patients, long-term use may result in goiter and severe hypothyroidism.

Use with caution in patients with preexisting thyroid disease (multinodular goiter, Graves’ disease, autoimmune thyroiditis), especially if therapy is expected to last longer than a few days.

Patients who have nodular thyroid disease (e.g., multinodular goiter) with heart disease are at increased risk of adverse effects; do not use in such patients. (See Contraindications under Cautions.)

Concomitant Illnesses

Use with caution in patients with Addison’s disease, cardiac disease, myotonia congenita, active tuberculosis, acute bronchitis, or renal impairment.

Use during Radiation Emergency

Use with caution and as directed by public authorities.

For radiation emergency, may be used in patients with preexisting thyroid disease who do not have nodular thyroid conditions with heart disease; however, consult clinician if potassium iodide therapy expected to last longer than a few days.

Eye or Skin Exposure

Vesication and desquamation may occur if strong iodine solution (also known as Lugol’s solution; commercially available but not FDA approved) is allowed to pool in contact with skin.

If accidental contact with skin or eyes occurs, flush with copious amounts of water for 15 minutes.

Specific Populations

Pregnancy

Category D.

Iodides readily cross the placenta; abnormal thyroid function (hypothyroidism) and/or goiter may occur in the neonate. Fetal thyroid may be most susceptible to effects of excess iodine at end of gestation.

Some experts state potassium iodide is contraindicated in pregnant women. AAP states use of potassium iodide as an expectorant is contraindicated during pregnancy.

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. If thyroidectomy necessary for treatment of hyperthyroidism during pregnancy, ATA and AACE recommend the surgery be performed during second trimester.

In radiation emergency, FDA recommends that pregnant women receive potassium iodide for their own protection and that of the fetus. However, because of risks of excess iodine to fetal thyroid function, avoid repeat administration during pregnancy, unless other protective measures not available. If repeat potassium iodide indicated in a pregnant woman, consultation with a clinician recommended and thyroid function monitoring may be indicated in the neonate.

If used during pregnancy or if pregnancy occurs during therapy, apprise patient of potential fetal hazard.

Lactation

Distributed into milk; possible rash and thyroid suppression in nursing infant.

AAP considers potassium iodide to be compatible with breast-feeding.

In radiation emergency, FDA recommends that lactating women receive potassium iodide for their own protection. However, avoid repeat administration in lactating women unless other protective measures are not available. If repeat administration indicated in a nursing woman, consultation with a clinician recommended; thyroid function monitoring may be indicated in a breast-fed neonate.

Because radioactive iodine is distributed into milk, some experts (including AAP) recommend that lactating women temporarily not breast-feed after a radiation emergency, unless no alternative is available; breast-feeding can resume when public authorities declare it safe to do so. Consider that administration of potassium iodide to lactating women potentially can reduce the radioiodine content of milk.

Pediatric Use

Safety and efficacy of potassium iodide oral solution containing 1 g/mL (also known as saturated solution of potassium iodide [SSKI]) not established in children. Has been used for treatment of cutaneous and lymphocutaneous sporotrichosis in children^†; recommended by IDSA as an alternative for treatment of these infections in children.

In radiation emergency, FDA states that benefits of potassium iodide outweigh risks in children, including neonates. However, to minimize risk of hypothyroidism during critical phase of brain development, avoid repeat administration in neonates ≤1 month of age unless other protective measures not available. If repeat potassium iodide necessary in neonate ≤1 month of age, consultation with clinician recommended.

Monitor neonates for development of hypothyroidism using TSH concentrations and, if indicated, free T₄; initiate thyroid replacement therapy if hypothyroidism occurs.

In 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).

Common Adverse Effects

GI effects (stomach upset, diarrhea, nausea, vomiting, stomach pain ), rash, salivary gland swelling or tenderness.

Drug Interactions

Specific Drugs and Laboratory Tests

Potassium Iodide Pharmacokinetics

Absorption

Bioavailability

Dietary iodine is well (>90%) absorbed under normal conditions.

Onset

Effects on thyroid function usually observed within 24 hours after potassium iodide dose and are maximal after 10–15 days of continuous therapy.

Duration

When administered during radiation emergency, thyroid protective effect against inhalation or ingestion exposure lasts about 24 hours.

Distribution

Extent

Distributes selectively into thyroid gland in amounts required for adequate thyroid hormone synthesis. Also distributes to a minor extent into salivary glands, breast, choroid plexus, and gastric mucosa.

Readily crosses placenta; distributed into milk.

Elimination

Elimination Route

Iodide not concentrated in thyroid gland is excreted principally in urine. Small amounts excreted in feces and sweat.

Stability

Storage

Oral

Tablets

20–25°C; keep in original foil pack and protect from moisture.

Oral Solution

65-mg/mL solution: Tight container at 25°C (may be exposed to 15–30°C); protect from light.

1-g/mL solution (also known as saturated solution of potassium iodide [SSKI]): Tight container at 15–30°C; protect from light. Crystallization may occur if exposed to cold temperatures; crystals will dissolve if solution is warmed and shaken. Discard if solution turns brownish-yellow.

Extemporaneous oral solution (liquid mixture) prepared using 65- or 130-mg tablets (see Extemporaneous Oral Solutions under Dosage and Administration): Store in refrigerator; discard any unused solution after 7 days.

Actions

• Iodine participates in a complex series of reactions in the thyroid gland to produce the thyroid hormones T₄ and T₃. Thyroid hormones are essential for human life since they regulate many key biochemical reactions (e.g., protein synthesis, enzymatic activity) and target the developing brain, muscle, heart, pituitary, and kidneys.

• In patients with hyperthyroidism, iodide rapidly inhibits release of thyroid hormones via direct effect on the thyroid gland and inhibits synthesis of thyroid hormones. Also attenuates effects of TSH mediated via cAMP and decreases vascularity of thyroid gland.

• When administered before or promptly after radioactive iodine exposure, potassium iodide blocks or reduces accumulation of radioactive iodine in the thyroid gland.

• Mechanism of action in treatment of cutaneous or lymphocutaneous sporotrichosis caused by S. schenckii not determined. Does not appear to increase monocyte or neutrophil killing of S. schenckii in vitro; however, exposure of yeast form of S. schenckii to various concentrations of iodine (iodine and potassium iodide solution) in vitro has resulted in rapid cell destruction.

• Mechanism of expectorant activity not clearly established; possibly increases respiratory tract secretions thereby decreasing mucus viscosity.

Advice to Patients

• During radiation emergency, importance of understanding the nature of the radiation hazard and potential benefits and adverse effects of potassium iodide. Importance of taking potassium iodide only as directed by public authorities. Necessity of adhering to other emergency measures recommended by public authorities.

• If hypersensitivity reaction (e.g., difficulty breathing/speaking/swallowing, shortness of breath, wheezing, rash, swelling of mouth/tongue/throat/face/hands/feet), fever and joint pain, irregular heart beat, or chest pain occurs, immediately discontinue potassium iodide and seek medical care.

• Importance of women informing clinicians if they are or plan to become pregnant or plan to breast-feed. Advise pregnant women of risks to the fetus.

• Importance of informing clinicians of existing or contemplated concomitant therapy, including prescription and OTC drugs.

• Importance of informing patients of other important precautionary information. (See Cautions.)

Preparations

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.

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