Administration of Stable Iodine in Nuclear Emergency

Radioactive isotopes of iodine form a significant part of the release in a nuclear reactor accident. When taken into the body, iodine compounds accumulate in the thyroid gland. Taking of stable iodine (a non-radioactive isotope of iodine) is a practicable measure to reduce the uptake of radioactive iodine by the thyroid gland.

Timing of Use

2. After an intake, the activity of radioactive iodine reaches 50% of the maximum in about 6 hours and the maximum in one or two days. To derive the maximum reduction of radiation dose to the thyroid, stable iodine should be administered before any intake of radioactive iodine, or as soon as practicable thereafter. If stable iodine is administered orally within the 6 hours preceding the intake of radioactive iodine, the protection provided is up to 98%. The protection is about 90% if stable iodine is administered at the time of inhalation and decreases with the delay in administration. But the protection can still be about 50% if stable iodine is administered within 4 to 6 hours after exposure.

Dosage

3. Stable iodine can be used either in the form of potassium iodide or potassium iodate. For an adult, the recommended dosage is 100 mg of iodine per day, which is equivalent to a dose of 130 mg of potassium iodide or 170 mg of potassium iodate per day. The recommended dosage for different age groups is as follows.

Age group KI(mg) KIO 3(mg) Equivalent iodine dosage Below 1 month 15 20 12.5 1 month - 3 years 32 42 25 3 years - 12years 65 85 50 Adult 130 170 100

4. If exposure to radioactive iodine lasts for more than a few days, it is advisable to repeat the administration. The risk of side effects, though small for a single administration, increases with the total dosage. Therefore stable iodine should not be taken as a long-term measure for protection against ingestion of radioactive iodine from foods. It is recommended that the total dosage of stable iodine compounds should not exceed 1 g of iodine equivalent for individuals over 1 year of age.

Risk associated with iodine prophylaxis

5. The risk associated with the administration of stable iodine to members of the public is small in countries with high dietary iodine intake, but increases in countries where there is a marked iodine deficiency in the diet. The main risks from intakes of stable iodine are in the occurrence of hypothyroidism, hyperthyroidism, thyrotoxicosis and goitre. When the correct dose is given to the public, the risk of side effects is relatively small to the very young, whilst it increases with age, and becoming pronounceable for the elderly.

6. In all cases, the decision as to whether to apply iodine prophylaxis should be carefully weighed against the risks of the induction of hypothyroidism or malignant tumours caused by the additional radiation dose that could be received if stable iodine were not administered.

7. Taking into account of the half-life of the predominant iodine isotope 1-131, which is 8 days, and that the release phase usually lasts for a relatively short period of time, iodine prophylaxis should be considered as a protective measure for inhalation only. For the ingestion pathway, other protective measures, such as food control and interdiction, should be employed instead of relying on iodine prophylaxis.

Use of iodine prophylaxis by emergency response personnel

8. The number of emergency response personnel with significant risk of radioactive iodine inhalation is likely to be relatively few in number. They should be given stable iodine, unless specific medical contra-indications pertain to individuals.

Use of iodine prophylaxis by members of the public

9. For members of the public distant from the accident site, ingestion is the major route of exposure. The introduction of appropriate control on contaminated food should reduce the radiation dose to the thyroid. The use of stable iodine may be indicated only if the thyroid dose is likely to exceed the prescribed intervention levels. The following groups of persons are most likely to benefit:

Pregnant women in the 2 nd and 3 rd trimester Lactating women Neonates (i.e. from birth to 1 month) Infants, children, and adolescents up to the age of 16 years

10. For adults over the age of about 40 to 45 years, the potential risks of stable iodine prophylaxis may well outweigh the potential benefits. Stable iodine is not recommended for large populations of this age group in the far field.

11. The balance of risks and benefits in adults between the ages of approximately 17 and 40 years is difficult to define and will depend upon a number of factors, one of which is the dietary iodine content of the country. In general, stable iodine should not be given to large populations in this age group in the far field.

Aide-memoire on Stable Iodine Prophylaxis

In the very unlikely event of a nuclear accident affecting the HKSAR, radioactive isotopes of iodine may be released into the environment. If the radioactive iodine is inhaled or ingested, it will concentrate in the thyroid gland leading to an increased risk of thyroid cancer.

2. Taking stable (non-radioactive) iodine before or shortly after exposure can reduce the uptake of radioactive iodine in the thyroid gland.

3. Potassium iodate is a form of stable iodine. Each tablet contains the recommended daily dose of iodine for adult for maximum protection of the thyroid gland.

4. The use of potassium iodate by emergency response staff under the Daya Bay Contingency Plan is entirely voluntary. When accident conditions warrant it, advice to take potassium iodate tablets will be given by the Director of Health directly or through the Emergency Monitoring and Support Centre of the Security Bureau on the advice of the Director of Health.

5. You should read and understand the directions before you take in the potassium iodate tablets.

CAUTION: Potassium iodate should not be used by anyone allergic to iodine. Exceeding the recommended daily dosage will not afford additional protection, but will increase the risk of side effects.

Directions for Use of Potassium Iodate Tablet Indications Taking potassium iodate before or soon after exposure to radioactive iodine can reduce the accumulation of the latter substance in the thyroid gland. Directions for use Use only when advised by the Director of Health or the Controller of the Emergency Monitoring and Support Centre of the Security Bureau. Description White round flat tablet. Dosage Each tablet contains 169 mg of potassium iodate. Adults - 1 tablet per day 3 years to 12 years - 1/2 tablet per day 1 month to 3 years - 1/4 tablet per day* # Birth to 1 month - 1/8 tablet per day Duration For emergency response staff, potassium iodate will usually be administered for at least 3 days even if there is no continuing exposure. It is unlikely that administration would be required beyond 10 days. Storage Store in a cool, dry place sheltered from light. Keep the container tightly closed. Warning People who are allergic to iodine should not use Potassium iodate. Keep the tablets out of children's reach In case of overdose or allergic reaction, contact a physician or go to the Accident and Emergency Department of a hospital. Who should avoid The following people should avoid taking potassium iodate: taking potassium 1. Those with known iodine sensitivity iodate 2. Those who are previously treated for active thyroid diseases (including goitres and auto-immune thyroid disease) because of an increased risk of relapse of thyrotoxicosis that may require definitive treatment. 3. Those having hypocomplementemic vasculitis and dermatitis herpetiformis How and when to Potassium iodate should be taken as soon as possible after the Director of Health take or the Controller of EMSC advises you or your department of the need to do so. potassium iodate You should take one dose every 24 hours. More will not help you. Larger doses will increase the risk of side effects. Side Effects The incidence of significant adverse reactions from such low-dose short-term administration of potassium iodate is expected to be low. Usually, side effects of potassium iodate may occur when people take higher doses for a long period. You should be careful not to take more than the recommended dose or take it for longer than you are told. Possible side effects include skin rashes, swelling of the salivary glands and “iodism” (metallic taste, burning sensation of the mouth and throat and sore teeth and gums), symptoms of a head cold and sometimes stomach upset and diarrhoea. A few people have an allergic reaction with more serious symptoms. These could be fever and joint pains, or swelling of parts of the face and body and at times severe shortness of breath requiring immediate medical attention. Taking iodine may rarely cause over-activity of the thyroid gland, under-activity of the thyroid gland or enlargement of the thyroid gland (goitre). What to do if side lf the side effects are severe or if you have an allergic reaction, stop taking effects occur potassium iodate and call a doctor or attend the Accident & Emergency Department of a hospital. * Dissolve 1 tablet in 20 mL of water and take in 5 mL # Dissolve 1 tablet in 40 mL of water and take in 5 mL