As per the WHO guidelines (1999) for stable Iodine Prophylaxis, the recommended adult dose is 100 mg of iodine (130 mg of KI) for persons above 12 years.
Children (3-12 y) - 50 mg of iodine (65 mg of KI)
Infants (1m to 3 months) - 25 mg (32 mg of KI)
Neonates (birth to 1 month) - 12. 5 mg (16 mg of KI)
To obtain full effectiveness of stable iodine for thyroidal blocking, it has to be administered shortly before exposure or as soon after as possible.This protective action is taken to prevent deterministic effects (Hypothyroidism) in the thyroid from the high levels (several Gy) of radiation dose to the thyroid from the uptake of radioiodines (mainly I-131, I-132 & I-133), released from the nuclear accidents, and to reduce the risk of stochastic effect - induction of thyroid cancer.
Intakes can take place through ingestion/inhalation routes. The best estimate of excess absolute cancer risk is 4.4 × 10 to the power -4 per Gray per year for persons exposed before the age of 15, and virtually no risk is observed for exposure after the age of 40.
The mass of thyroid varies with the age. Indian data (Source: Asian Reference Man Data, IAEA-TECDOC-1005) show variation from 1.5 gm (newborn), 8 gm (10 years) to 19 gm (male adults). Lower the mass, higher is the dose received for a given uptake and hence greater is the cancer risk.
There is a greater need to protect the thyroid gland of the pregnant woman since the iodine uptake can be increased as compared to other adults. As much as 1/4 of the iodine taken by the mother may be secreted in the milk within 24 h. Newborn infants are quite likely the critical group of concern when deciding on the implementation of stable iodine prophylaxis.
A generic intervention level of 100 mGy avertable dose is recommended for all age groups. However, the recommended intervention level for childhood exposure is 10 mGy avertable dose to the thyroid.
(Source: WHO Guidelines for Iodine Prophylaxis following Nuclear Accidents - Update 1999)
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