[Effect of antithyroid medication on the effective half-life and uptake of 131-iodine following radioiodine therapy]

Abstract

Aim: A radioiodine therapy (RIT) in thyrotoxic patients receiving antithyroid drugs (ATD) leads in comparison to nonpretreated patients either to higher therapeutic doses or to higher treatment failure rates. Aim of this study was to optimize the effect of RIT in patients pretreated with ATD.

Methods: Therefore, the influence of ATD was assessed in 109 patients with shortened effective half-life of 131I. RIT was performed under stationary conditions. Radioiodine activity of the thyroid gland was measured twice a day. In 77 patients antithyroid medication was stopped three days after RIT. The progress of the first RIT and of a second radioiodine application, which still was necessary in 29 patients, was compared to 32 patients receiving ATD, continuously.

Results: Values of effective half-life for 131I rose significantly from 3.2 +/- 0.2 to 5.7 +/- 0.2 days (Graves' disease: 3.4 to 5.7 days; toxic goiters' disease: multifocal autonomy 3.2 to 6.2 days; unifocal autonomy 2.5 auf 5.0 days) 2-3 days after stopping ATD. There was an increase of the 131I-uptake of a second after stopping ATD, too. In contrast, 131I-uptake of a second RIT decreased significantly in patients receiving ATD, continuously.

Conclusion: Effective half-life and uptake of 131I was affected significantly by ATD. The stop taking of ATD after RIT is useful to improve an apparent insufficient RIT in thyrotoxic patients receiving ATD.