Potassium iodide is indicated as a thyroid-blocking agent to prevent the uptake of radioactive iodine, for example after a nuclear accident or during a nuclear medicine investigation before administering a radioiodinated compound, which is metabolised to iodide or which contains radioiodine impurities.

Posology

Nuclear accident

Iodine prophylaxis should be performed in case of a nuclear accident, when radioactive iodine is released, in all people involved including children and pregnant and breastfeeding women located in the endangered area. People with known iodine sensitivity or with a history of active treatment of thyroid disorders should consult their physician. When the nuclear accident is announced the required doses of potassium iodide are as follows:

A single daily dose should be administered. This will protect against exposure lasting up to 24 hours (see section 4.4).

Owing to the sensitivity of the neonate and foetus thyroid to large doses of iodine, repeated administration of stable iodine should be avoided for neonates and pregnant and lactating women. Neonates will not require further doses. Pregnant and breastfeeding women should take a maximum of two doses.

For children the medicine may be crushed and mixed with milk, water or juice before administration.

Nuclear medicine investigation

When ThySat 65 mg tablets are used as a blocking agent before administering a radioiodinated compound, which is metabolised to iodide or which contains radioiodine impurities, an oral dose of 130 mg (2 tablets) in adults will reduce thyroid uptake to less than 1% of normal. This dose should be administered on or before the day of the investigation and then daily until the estimated activity of radioiodine in the body has fallen to appropriate levels.

In children of 3 to 12 years 50% of the adult dose should be given and in children of 1 month to 3 years the dose should be 25% of the adult dose.

Potassium iodide should not be given when radioiodine is being administered for the purpose of diagnostic imaging or treatment of the thyroid gland.

Method of administration

For oral administration.

Hypersensitivity to potassium iodide (see also sections 4.2 and 4.5) or to any of the excipients listed in section 6.1

In cases of exposure to radioiodine from nuclear accidents, dosing of potassium iodide should be based on emergency plans and predetermined operational intervention levels. Risk benefit of administration of stable radioiodine should be considered for the different age groups at risk. Pregnant and lactating women, neonates, infants and children should be treated first. A single dose of potassium iodide gives adequate protection for one day. Prolonged exposure may require repeat dosing, however repeat dosing in the neonate, and in pregnant and lactating women should be avoided (see section 4.2). Iodine prophylaxis is used against inhaled radioiodine and should not be the main prophylaxis for ingested contamination.

Patients with thyrotoxicosis treated medically, or patients with a past history of thyrotoxicosis treated medically who are now off treatment and apparently in remission, may be at risk.

Iodine induced hyperthyroidism may be precipitated in patients with asymptomatic nodular goitre or latent Graves` disease, who are not under medical care.

Potassium salts should be given cautiously to patients with renal or adrenal insufficiency, acute dehydration or heat cramp.

Care should be exercised if potassium salts are given concomitantly with potassium-sparing diuretics, as hyperkalaemia may result (see section 4.5).

The potential benefit of iodine prophylaxis is greatest in the young. The thyroid of the foetus, neonate and young infant has a higher yearly thyroid cancer risk per unit dose of radioactive iodine than the thyroid of an adult.

Potassium iodide prophylaxis is not usually indicated in adults over 40 unless doses to the thyroid from inhalation rise to levels threatening thyroid function, that is of the order of about 5 Gy. The risk of thyroid cancer is extremely low in this group whereas the incidence of thyroid disease is higher in this group therefore the risk of iodine induced thyroid complications are higher.

Paediatric Population

Neonates in the first days of life are at particular risk from exposure to radioactive iodine and blocking of thyroid function by overload of potassium iodide. The fraction of radioactive uptake is fourfold greater than all other age groups. The neonatal thyroid is especially sensitive to functional blocking caused by overload of potassium iodide. Transient hypothyroidism during this early period of brain development can result in loss of intellectual capacity. If stable iodine is given to neonates close follow up of thyroid function is essential. For neonates who have been administered potassium iodide in the first few weeks of life TSH levels and, if necessary, T4 levels should be monitored and appropriate replacement therapy given.

Several drugs, such as captopril and enalapril can cause hyperkalaemia and this effect may be enhanced if potassium iodide is also administered.

The effect of quinidine on the heart is increased by increased plasma concentration of potassium.

Hyperkalaemia results from the interaction between potassium salts and potassium sparing diuretics such as amiloride or triamterene or aldosterone antagonists (see section 4.4).

The effects of iodine and iodides on the thyroid may be altered by other compounds which may also have an effect on the thyroid, including amiodarone and lithium. The hypothyroid and goitrogenic effects of lithium carbonate and iodides can be additive if they are given concurrently.

Pregnancy

Teratogenic effects such as congenital goitre and hypothyroidism have been reported when iodides are administered to pregnant women.

Prophylactic administration of iodide to the pregnant mother should also be effective for the foetus.

Throughout pregnancy the number of doses of potassium iodide should be kept to a minimum and repeat doses should be avoided (see section 4.2). In areas of iodine deficiency prolonged dosage could lead to maternal or foetal thyroid blockage with possible consequences for foetal development. If potassium iodide is administered late in pregnancy, the thyroid function of the new-born should be monitored. This is generally met by routine screening in the neonatal period. For neonates who have been administered potassium iodide in the first few weeks of life TSH levels and, if necessary, T4 levels should be monitored and appropriate replacement therapy given.

Pregnant women with active hyperthyroidism must not take potassium iodide because of the risk of foetal thyroid blockage.

Breast-feeding

Iodine is actively transported into breast milk, however those breast feeding should continue to do so (see section 5.2). Lactating women should avoid repeat doses (see section 4.2).

Fertility

No human data on the effect of active substance potassium iodide on fertility are available. There is no preclinical information available on the effect of the active substance potassium iodide on mating or fertility.

ThySat 65 mg tablets have no or negligible influence on the ability to drive and use machines.

Undesirable effects are listed by MedDRA System Organ Classes.

Assessment of undesirable effects is based on the following frequency groupings:

Very common: ≥ 1/10

Common: ≥ 1/100 to <1/10

Uncommon: ≥ 1/1,000 to <1/100

Rare: ≥ 1/10,000 to <1/1,000

Very rare: <1/10,000

Not known: cannot be estimated from the available data

Continued administration may lead to mental depression, nervousness, sexual impotence and insomnia.

Reporting of suspected adverse reactions

Reporting suspected adverse reactions after authorisation of the medicinal product is important. It allows continued monitoring of the benefit/risk balance of the medicinal product. Healthcare professionals are asked to report any suspected adverse reactions via Yellow Card Scheme. Website: www.mhra.gov.uk/yellowcard or search for MHRA Yellow Card in the Google Play or Apple App Store.

In overdose, symptoms of iodism such as headache, pain and swelling of the salivary glands, fever or laryngitis, swelling or inflammation of the throat, gastrointestinal upset and diarrhoea can occur. Pulmonary oedema can also occur.

Acute ingestion of iodine can result in corrosive injury of the gastrointestinal tract and renal damage. Cardiopulmonary collapse due to circulatory failure should be treated by maintenance of airway and stabilisation of the circulation. Oedema of the glottis resulting in asphyxia or aspiration pneumonia can occur.

Gastric lavage should not be considered due to the possibility of corrosive injury. Activated charcoal may be considered in iodide poisoning if the patient presents within 1 hour of ingestion. Give milk or starch-based food.

Pharmacotherapeutic group: Antidotes

ATC code: V03AB21 Potassium iodide

When exposed to radioactive iodine, potassium iodide prevents damage by radioactive iodine to the thyroid gland due to saturation by non-radioactive iodine of thyroid gland preventing the uptake of radioactive iodine from contaminated air, water, milk and other foods. IN THE CASE OF NUCLEAR ACCIDENT, IT IS NECESSARY TO ADMINISTER POTASSIUM IODIDE WITHIN ONE HOUR! Administration within one hour results in the thyroid gland being saturated with non-radioactive iodine (more than 85%). For every hours' delay the percentage of saturation decreases: after three hours the saturation with non-radioactive iodine is 50%. Administration of the iodine after six hours of exposure is of no benefit. Therefore, it is very important that public notice of possible nuclear accident is given as soon as possible.

The human body contains 20 to 50 mg of iodine. The average daily consumption is 150 to 200 µ g. Iodine uptake by the thyroid gland is 80-fold higher compared with other organs. The human body is able to metabolise doses even manyfold higher than the daily recommended dose, mainly via urine, enterohepatic circulation and salivary glands (after the administration of one single dose of 3 g potassium iodide the dose is completely eliminated after 75 hours, 89% via urine).

As much as a quarter of the iodine taken by the mother can be secreted in the breast milk within 24 hours. Potassium iodide can partially block transport of radioiodine in the milk. The same criteria should apply when selecting a dose of potassium iodide to protect a lactating mother as that used for other young adults under 40 years of age.

A single high dose has been found to be teratogenic in rats. In another study in rats, the administration of high daily iodine doses led to incomplete parturition, failure of lactation and reduced mothering activities. The administration of a iodine-containing substances to pigs had no teratogenic effects.

In a long term study where rats received potassium iodide in the drinking water for two years the development of squamous cell carcinomas in the salivary glands were observed.

Cellulose, microcrystalline

Talc

Silica, colloidal anhydrous

Not applicable.

6 years

Do not store above 25° C.

Keep the blister in the outer carton in order to protect from light and moisture.

Blister (white, opaque PVC/PVDC foil / Al foil with printing), package insert leaflet, outer paper folder.

Size of packing: 2, 4, 10 or 100 tablets

Not all pack sizes may be marketed.

Any unused medicinal product or waste material should be disposed of in accordance with local requirements.