Potassium iodide

Potassium iodide is an active ingredient with thyroid-protective and expectorant properties. It is administered in oral tablet form during a nuclear radiation emergency to prevent the absorption of radioactive iodine. This protects the thyroid gland from carcinogenic radiation. In some European countries, potassium iodide tablets are stockpiled, for example, in schools and childcare facilities (Austria), obtained free of charge from pharmacies (Germany), or distributed to communities in the vicinity of nuclear facilities (Switzerland). In most cases, the population is asked to take it by radio.

As an adjunct to other thyroid function-inhibiting drugs, potassium iodide can also be used in the treatment of hyperthyroidism, e.g., preoperatively to induce thyroid regression.

Pharmacodynamics

Potassium iodide blocks the formation and release of thyroid hormones, thereby reducing the visibility of blood vessels on the body. Thyroid tissue solidifies, thyroid cells decrease in size, protein-bound inactivated thyroxine (thyroid hormone) reaccumulates, and bound iodine levels increase. For protection during radiation exposure, potassium iodide inhibits the uptake of radioactive iodine isotopes by the thyroid gland and minimizes the risk of radiation-induced thyroid tumors. Administration a few hours after the arrival of radioactive air masses already reduces the efficiency of the agent by 15% or 50%. Because of this, it is especially important to take potassium iodide tablets quickly in such cases.

Pharmacokinetics

Potassium iodide taken orally is practically completely absorbed in the small intestine. Prior to absorption, iodine and iodate are reduced to iodide in the intestine. The retained iodide is stored in the thyroid gland, salivary glands, mammary glands and stomach. The iodide circulating in the blood is almost completely excreted by the kidneys within a day, but can also be found in tears, sweat and milk.

Drug interactions

Simultaneous use of lithium promotes enlargement of the thyroid gland (goiter) and development of hypothyroidism. Increased blood potassium concentrations may occur while taking potassium-sparing diuretic (diuretic) medications. The effects of drugs used to treat hyperthyroidism (methimazole, propylthiouracil) may be attenuated by potassium iodide.

Contraindications

Because some individuals are markedly sensitive to iodine, potassium iodide should be used with caution during initial administration. Patients at risk for iodine-induced side effects include those with hypocomplementemic vasculitis (chronic vasculitis), thyroid swelling, or autoimmune thyroid disease. During pregnancy, potassium iodide use may cause thyroid problems in the mother and child, although the protective effect against radioactive radiation (in the event of exposure) outweighs the risk of thyroid damage. In patients with tuberculosis, potassium iodide should be used with extreme caution, as well as in autoimmune thyroid disease, since iodine has a stimulating effect on thyroid autoimmunity.

Side effects

The risk of side effects increases with age. Adverse side effects include:

• Indigestion
• Metallic taste
• Conjunctivitis
• Swelling of the salivary glands
• Headache
• Cough
• Bronchitis
• pulmonary edema
• palpitations
• Restlessness

In rare cases, hyperthyroidism or hypothyroidism and hypersensitivity reactions occur.

Toxicological data

LD50 (rats, intravenous): 285 mg/kg