Source: Health Products Regulatory Authority (IE) Revision Year: 2021 Publisher: G.L. Pharma GmbH, Schlossplatz 1, 8502 Lannach, Austria
Pharmacotherapeutic group: Antidotes
ATC code: V03AB21
In cases of a nuclear accident radioactive iodine may form a large amount of the output.
Because of its high volatility it can be easily inhaled and absorbed via the lungs.
Radioactive iodine can be detected in large amounts in the thyroid if exposed to very strong radiation, by which the risk for local damage is increased. The uptake of radioactive iodine by the thyroid can be blocked by saturation, by the early intake of a high dose of stable iodide. A dose of 130 mg (= 2 tablets) potassium iodide provides complete saturation. The risk for thyroid cancer due to exposition to radioactive iodine is higher in younger persons. Generally it is assumed that foetusses of more than 12 weeks, newborns and children have got the highest risk because their thyroid is still in growth.
Orally administered iodine is converted in inorganic iodide and it is almost completely absorbed from the gastrointestinal tract.
Food causes a delay of 10-15 minutes. Absorption is completed 2 hours after oral administration.
At intake on an empty stomach, radioactive 131I is detected in the neck area after about 3 minutes.
Physiological serum concentrations in humans vary from 1 to 5 µg/l (40 to 80 nmol/l) at daily iodine intakes of 150 to 250 µg.
Iodine in the systemic circulation is being exchanged rapidly between erythrocytes and extracellular liquid. The total amount of inorganic iodide in this pool is about 250 µg.
The uptake of iodide by the thyroid depends on volume, thyroid function, plasma iodide concentration and physiological age. Active iodide transport in extrathyroidal tissues such as salivary gland, lacrimal gland, choroid plexus, ciliary body of the eye, skin, placenta, gastric mucosa, and in mammary glands during lactation takes place to a minor extent.
Iodine passes the placental barrier and is taken up by the foetal thyroid. It was found that uptake starts around a foetal age of 3 months. The highest concentration was found at a foetal age of about 6 months. In children and adolescents the iodine uptake by the thyroid is higher than in adults. In elderly persons, however, a significant reduction was observed.
If iodine doses are administered on an empty stomach, the half maximum thyroid uptake is reached after approximately 4 hours, although the duration is between 2.5 and 6.5 hours for most of the patients.
Iodine undergoes organification in the thyroid, i.e. it is being oxidized and linked to thyroglobuline. The thyroid hormones thyroxine (T4) and triiodothyronine (T3) are being synthetized via oxidative condensation of the iodated intermediates monoiodotyrosine (MIT) and diiodotyrosine (DIT) inside the thyroglobuline complex. Hormone secretion takes place by way of pinocytosis followed by proteolytical release of T4 and T3 from thyroglobuline.
The main elimination (95%) occurs via the kidneys and amounts for approximately 30 to 40 ml/min.
Renal elimination rate is not influenced by iodine intake or iodine serum levels.
In pregnant women there is an increased elimination of iodide which may cause iodine deficiency.
Only small amounts of iodine have been found in faeces (approximately 1% of the total iodine elimination).
Iodine is being excreted into breast milk in considerable amounts (10-15% of the intake).
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 substance 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.
Apart from the information provided in the other sections, there is no additional relevant information from animal studies.
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