# Efficacy of radioactive iodine therapy with concomitant antithyroid drugs in Japanese patients with Graves’ disease: a retrospective observational study

## TL;DR

This study compares the effectiveness of radioactive iodine therapy with and without antithyroid drugs in Japanese Graves’ disease patients.

## Contribution

It is the first to evaluate concomitant antithyroid drugs during RIT in a high-iodine-intake population.

## Key findings

- Withdrawing antithyroid drugs before RIT led to higher cure rates within 12 months.
- Concomitant antithyroid drugs were associated with lower cure rates compared to standard RIT.
- Patients in the concomitant drug group had higher baseline antithyroid drug doses.

## Abstract

Radioactive iodine therapy (RIT) for Graves’ disease (GD) often involves antithyroid drugs (ATDs) withdrawal and the exacerbation of thyrotoxicosis. This study investigated the efficacy of RIT with concomitant ATDs (CATD) versus temporary ATDs withdrawal in Japanese patients with GD, a population with high iodine intake according to global standards.

This retrospective observational study included 179 patients with GD who visited the University of Tsukuba Hospital. Propensity score matching (balancing age, sex, thyroid weight, free T4) created comparable groups of 15 patients each: CATD(-) withdrawing ATDs and CATD(+) continuing ATDs during RIT. Cure was defined as hypothyroidism or euthyroidism achieved without ATDs or potassium iodide. Post-matching, the CATD(+) group received significantly higher baseline ATD doses (median 600 vs. 200 mg/day propylthiouracil-equivalent; p < 0.008). The cure rate within 12 months after RIT was significantly higher in the CATD(-) group than in the CATD(+) group (n = 12 [80.0%] vs. n = 4 [26.7%]; p = 0.005). CATD may be associated with a lower cure rate within 12 months compared with standard RIT involving temporary ATD discontinuation. We suggest further prospective studies to confirm the efficacy of radioactive iodine therapy with concomitant antithyroid drugs in high iodine intake country.

The online version contains supplementary material available at 10.1186/s13104-025-07558-9.