Usage
Potassium iodide is primarily prescribed to protect the thyroid gland from absorbing radioactive iodine in the event of a radiation emergency (such as a nuclear power plant accident). It is also used to treat hyperthyroidism, prepare patients for thyroid surgery, manage thyrotoxic crisis, and treat some skin conditions (like sporotrichosis) and certain types of bronchitis. It is also used, although less often, to treat iodine deficiency.
Its pharmacological classifications include:
- Thyroid blocking agent: In radiation emergencies
- Expectorant: In certain respiratory conditions
- Antithyroid agent: At high doses for hyperthyroidism
Mechanism of Action (Radiation Protection): Potassium iodide saturates the thyroid gland with stable iodine, preventing the uptake of radioactive iodine isotopes, thus reducing the risk of thyroid cancer.
Alternate Names
- SSKI (Saturated Solution of Potassium Iodide)
- Lugol’s solution (Strong iodine solution)
- Pima Syrup
- Iosat
- ThyroSafe
- ThyroShield
How It Works
Pharmacodynamics: Potassium iodide’s primary effect relevant to radiation exposure is preventing radioactive iodine uptake by the thyroid. At higher doses used in hyperthyroidism, it inhibits thyroid hormone synthesis and release. In respiratory conditions, it acts as an expectorant, thinning mucus secretions.
Pharmacokinetics: Potassium iodide is rapidly absorbed from the gastrointestinal tract. It is distributed throughout the extracellular fluid, concentrating in the thyroid gland, salivary glands, gastric mucosa, and breast milk. It is primarily excreted by the kidneys.
Mode of Action: In radiation emergencies, potassium iodide competitively inhibits the uptake of radioactive iodine by the sodium-iodide symporter (NIS) located on thyroid follicular cells. In hyperthyroidism, it inhibits thyroid hormone synthesis and release by interfering with iodine organification and coupling of iodotyrosines.
Elimination: Primarily renal excretion.
Dosage
Standard Dosage
Adults:
- Radiation Protection: 130 mg orally once daily. Ideally given 1-48 hours before exposure, continued until the risk has passed.
- Hyperthyroidism: 250 mg (as SSKI) orally three times a day.
- Preoperative Thyroid Surgery: 5-10 drops (0.25-0.5 mL of SSKI, or 5-7 drops of Lugol’s solution) three times a day for 10 days before surgery.
- Expectorant: 300-600 mg orally three to four times a day.
- Iodine Deficiency: 0.3 to 1 mL of SSKI three to four times a day.
Children:
- Radiation Protection:
- Infants under 1 month: 16.25 mg orally once daily
- 1 month to 3 years: 32.5 mg orally once daily
- 3 years to 12 years: 65 mg orally once daily
- Over 12 years approaching adult size (> 70 kg): 130 mg orally once daily
- Other indications: Dosing must be determined by a doctor.
Special Cases:
- Elderly Patients: Generally same as adult dose, with careful monitoring for adverse effects. For radiation protection, not recommended in those over 45 except in situations with predicted high thyroid exposure.
- Patients with Renal Impairment: Dose adjustment may be needed.
- Patients with Hepatic Dysfunction: No specific adjustments, but close monitoring is advisable.
- Patients with Comorbid Conditions: Careful evaluation and dose adjustment may be necessary, particularly in those with thyroid disorders, heart disease, or kidney disease. Avoid in patients with Addison’s disease, dermatitis herpetiformis or hypocomplementemic vasculitis.
Clinical Use Cases
Dosing in these clinical settings typically follows the standard adult guidelines for radiation protection (130 mg once daily) unless specifically contraindicated.
Dosage Adjustments
Adjustments may be necessary based on renal/hepatic function, thyroid status, and other medical conditions as determined by a physician.
Side Effects
Common Side Effects
- Nausea, vomiting, diarrhea, stomach pain
- Metallic taste
- Salivary gland swelling/tenderness
- Skin rash
Rare but Serious Side Effects
- Angioedema
- Iodism (burning mouth/throat, sore teeth/gums, head cold symptoms)
- Hyperkalemia
Long-Term Effects
- Hypothyroidism (with prolonged use)
- Goiter
Adverse Drug Reactions (ADR)
- Severe allergic reactions (anaphylaxis)
- Thyroid dysfunction
Contraindications
- Hypersensitivity to iodine
- Hyperthyroidism (except when used to treat thyrotoxic crisis under strict medical supervision)
- Dermatitis herpetiformis
- Hypocomplementemic vasculitis
Drug Interactions
- Antithyroid medications: Increased risk of hypothyroidism
- Lithium: Increased risk of hypothyroidism
- Potassium-sparing diuretics, ACE inhibitors, potassium supplements: Increased risk of hyperkalemia
- Other potential interactions: Consult a comprehensive drug interaction database.
Pregnancy and Breastfeeding
- Pregnancy: Can cause fetal harm (congenital goiter, hypothyroidism). Only use in radiation emergencies if absolutely necessary, limiting repeat doses.
- Breastfeeding: Iodine is excreted in breast milk. Neonatal thyroid function should be monitored. In radiation emergencies, a single dose may be given to the mother, and the infant should also receive potassium iodide.
Drug Profile Summary
- Mechanism of Action: Blocks radioactive iodine uptake by the thyroid; inhibits thyroid hormone synthesis/release (high doses); thins mucus secretions (expectorant use).
- Side Effects: Nausea, vomiting, diarrhea, metallic taste, salivary gland swelling, skin rash.
- Contraindications: Iodine hypersensitivity, hyperthyroidism, dermatitis herpetiformis, hypocomplementemic vasculitis.
- Drug Interactions: Antithyroid medications, lithium, potassium-sparing diuretics, ACE inhibitors.
- Pregnancy & Breastfeeding: Avoid in pregnancy unless essential for radiation protection. Use with caution during breastfeeding. Monitor infant’s thyroid function.
- Dosage: Varies based on indication and age. See dosage section.
- Monitoring Parameters: Thyroid function tests (TSH, T4), serum potassium levels.
Popular Combinations
Used in combination with other emergency measures during radiation emergencies.
Precautions
- General Precautions: Assess for iodine allergy and thyroid function. Monitor for adverse effects.
- Specific Populations: Caution in pregnancy and breastfeeding. Close monitoring in newborns and infants. Not generally recommended in those over 45 for radiation protection, except in high exposure situations.
- Lifestyle Considerations: None specifically associated with short-term use for radiation protection.
FAQs (Frequently Asked Questions)
Q1: What is the recommended dosage for Potassium Iodide?
A: The dosage varies depending on age and indication. Please refer to the detailed Dosage section.
Q2: How soon after radiation exposure should KI be taken?
A: Ideally, 1-48 hours before exposure, but still effective up to 8 hours afterward.
Q3: What are the common side effects of KI?
A: Common side effects include gastrointestinal upset (nausea, vomiting, diarrhea), metallic taste, and salivary gland swelling/tenderness.
Q4: Who should not take KI?
A: Individuals with iodine hypersensitivity, hyperthyroidism (except specific treatment scenarios), dermatitis herpetiformis, and hypocomplementemic vasculitis.
Q5: Can pregnant or breastfeeding women take KI?
A: Use with extreme caution in pregnancy only if absolutely necessary for radiation protection. Breastfeeding mothers should take a single dose in a radiation emergency, and the infant also needs to be given KI.
Q6: How does KI work to protect the thyroid?
A: KI saturates the thyroid gland with stable iodine, preventing it from absorbing radioactive iodine.
Q7: What is the difference between potassium iodide and potassium iodate?
A: Both are sources of iodine, but potassium iodate is more stable with a longer shelf life. Dosing may vary, so consult reliable sources for specific guidelines.
Q8: What are the long-term effects of KI?
A: Long-term use of high doses of KI may lead to hypothyroidism.
Q9: What are the most serious side effects of KI?
A: Serious side effects are rare but can include severe allergic reactions (anaphylaxis) and significant thyroid dysfunction.
Q10: Can KI protect against all types of radiation?
A: No, KI only protects the thyroid from radioactive iodine, not other radioactive elements or types of radiation.
