Medical Notes on Stable Iodine Prophylaxis

Medical Notes about Stable Iodine Prophylaxis (Last updated 31st July 2002)

These notes are intended to give medical information such as dosage, contraindications etc. for stable iodine prophylaxis in the unlikely event of a release of radioactive iodine from a nuclear facility. Based on information from the Chief Medical Officer, they will be of interest to general practitioners and members of the public who wish to know more about the medical aspects of stable iodine prophylaxis. Practical arrangements are covered elsewhere on this site.

Rationale for the Administration of Iodine Prophylaxis

In certain types of nuclear accidents, it is possible that radioactive isotopes of iodine could be released into the environment. Since the thyroid gland absorbs iodine - as a precursor of thyroid hormones - there is a possibility that radioactive iodine could accumulate in the thyroid glands of exposed individuals and lead to an increased risk, in the long term, of thyroid cancer. If stable iodine is taken it "fills up" the thyroid with non-radioactive iodine and prevents the accumulation of radioactive iodine. It provides no other protection against radiological exposure.

Population Groups and Dosage

The UK government considers that if the severity of an accident is such that the intervention levels are exceeded and iodine tablets are indicated, potassium iodate should be given to all population groups. They include:

pregnant women (all trimesters) and lactating women
neonates and infants, including breast-fed babies
children and adolescents
adults, including off-site emergency personnel.

Each 85 mg potassium iodate tablet contains 50 mg equivalent mass of stable iodine. The dosage schedule is as follows:

Patient Equivalent mass of iodine Potassium iodate

adults 100 mg 170 mg (2 tablets)

children aged 3–12 years 50 mg 85 mg (1 tablet)

children aged 1 month–3 years 25 mg 42.5 mg (1/2 tablet)

neonates (birth–1 month) 12.5 mg 21.25 mg *

*It should be noted that the use of a 50 mg equivalent potassium iodate tablet would require special provision to be made for neonates to provide them with a dose of 12.5 mg. In circumstances where only tablets are available (i.e. at home), neonates can receive up to 25 mg (i.e. half a tablet).

Follow up of neonates following iodine prophylaxis

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Contraindications

In an emergency situation in the UK it would not be necessary to regard previously treated or active thyroid disease as contraindications to taking stable iodine. Although it was recognised that stable iodine can cause a relapse in patients who are currently, or have been previously treated medically for thyrotoxicosis, it was considered that there was no clear evidence for there being a likelihood of relapse at the dose recommended. In any case, the risk to patients in the UK who are under medical supervision would be very low. Furthermore, those at most risk would be people with asymptomatic nodular goitre and latent Grave's disease who are not likely to have come to medical attention and cannot therefore be easily identified. People with hypothyroidism or with thyrotoxicosis treated either surgically or with radioiodine would not be at risk from stable iodine.

Contraindications in the UK are:

known iodine sensitivity; this includes sensitivity to topical iodine preparations as well as allergic reactions to ingested or parenteral iodine e.g. in X-ray contrast media;
the following rare conditions:
- hypocomplementaemic vasculitis – this includes patients with vasculitis characterised by low serum complement. There have been cases reported in the literature (Potassium iodide sensitivity in four patients with hypocomplementaemic vasculitis, by Curd JG et al. Annals of Internal Medicine, 1979; 91: 853-7) which suggest that hypocomplementaemic vasculitis in patients with chronic urticaria or SLE [systemic lupus erythematosus] may be associated with KI sensitivity and in these patients KI can precipitate severe side effects. Although the effect of exposure to potassium iodate is not known, it is presumed to be the same as potassium iodide.
- Dermatitis herpetiformis – other conditions associated with gluten sensitivity, such as coeliac disease, are not contraindications.

Further Information

Please contact the Health Protection Unit for further information on this topic.

Patient	Equivalent mass of iodine	Potassium iodate
adults	100 mg	170 mg (2 tablets)
children aged 3–12 years	50 mg	85 mg (1 tablet)
children aged 1 month–3 years	25 mg	42.5 mg (1/2 tablet)
neonates (birth–1 month)	12.5 mg	21.25 mg *
*It should be noted that the use of a 50 mg equivalent potassium iodate tablet would require special provision to be made for neonates to provide them with a dose of 12.5 mg. In circumstances where only tablets are available (i.e. at home), neonates can receive up to 25 mg (i.e. half a tablet).