The effect of carbimazole following radioiodine therapy on radiation dose to the thyroid.

Radioiodine in the thyroid gland after a therapy dose of 131I was measured serially in 7 patients without Carbimazole, and in 11 patients starting Carbimazole 60 mg daily fourteen days after the therapy dose. Effective half-life for radioiodine in the gland initially 5.53 plus or minus 1.08 days fell to 4.26 plus or minus 1.12 days (p less than 0.01) during Carbimazole, and returned to 5.83 plus or minus 1.21 days (NS) after stopping the drug. The radiation dose to the thyroid from a given therapy dose of 131I followed by Carbimazole was calculated to be 97% of that without Carbimazole when he drug was started after 14 days, and 90% and 75% when the drug was started after 7 days and 1 day respectively.