Effect of delay time on effectiveness of stable iodine prophylaxis after intake of radioiodine

Reviews the experimental literature bearing on the effectiveness of stable iodine in reducing radioiodine doses to the thyroid when it is taken some time after inhalation of the radioiodine. One conclusion drawn for the UK population is that in order to avert 50% of the thyroid dose for an average adult the stable iodine must be administered within 4 h of exposure, and that to provide this level of protection for almost all adults it must be administered within 2 h. To avert 80% of the dose for the average adult, the stable iodine must be administered within an hour. This is in contrast to the statement in ICRP Publication 40, repeated by other authorities, that administration 6 h after exposure can block about 50% of the dose. This conclusion may be relevant for those responsible for planning the distribution of stable iodine, and considering the merits of predistribution.