Thyroid blockade during a radiation emergency in iodine-rich areas: effect of a stable-iodine dosage.

We examined the effect of stable iodine on thyroid gland blockade in patients with hyperthyroidism in order to make a preliminary evaluation of the appropriate dose of iodine prophylaxis in the event of a radiation emergency in Japan in which radioiodine is released to the environment. Eight patients were orally given single doses of 50 mg or 100 mg of potassium iodide, which contained 38 mg and 76 mg of iodide, respectively. Both doses significantly suppressed a thyroid uptake of (123)I for 24 h (p = 0.03). The protective effects at 24 h were 73.3% and 79.5%, respectively. No side effects were observed during the trial. The present study demonstrates that a single oral administration of 38 mg of iodide produces a thyroid-blocking effect equivalent to that of 76 mg of iodide, suggesting that a reevaluation of the stable iodine dosage during radiation emergencies in iodine-rich areas such as Japan is warranted.