Background: In view of the new national guideline on
thyroid dysfunction, the evidence base for current practice as well as the new guideline is assessed with regard to the use of antithyroid drugs (ATDs) before and after radioiodine (<sup>131</sup>I) therapy.
Methods: In December 2006, we surveyed 16 hospitals by telephone about different aspects of their antithyroid drug regimen: all eight academic centres and eight nonacademic teaching hospitals. The literature was searched for an evidence-based answer to each question in the inquiry.
Results: 13 of 16 hospitals (81%) use antithyroid drugs for pretreatment before (<sup>131</sup>I. ATDs are discontinued on average four days before (<sup>131</sup>I or diagnostic scan. However, 27% stop only three days beforehand, which may diminish the effect of (<sup>131</sup>I. Propylthiouracil (PTU) is also withdrawn four days before (<sup>131</sup>I,
although the literature shows that PTU diminishes the effect of (<sup>131</sup>I even if it is stopped 15 days beforehand. Resumption of ATDs after (<sup>131</sup>I to prevent thyrotoxicosis is common practice (81%). One hospital (6%) never restarts ATDs, two (13%) only by indication. Adjunctive treatment consists of combination therapy in 93%, is usually resumed within two days after (<sup>131</sup>I therapy, and then continued for two to six months. Routine adjunctive treatment is not evidence-based and may be limited to a high-risk subset, especially elderly patients (>70 years) and patients with cardiac comorbidity. Resumption of ATDs within five to seven days after 131I may diminish the effect of (<sup>131</sup>I.
Conclusion: Antithyroid drug regimens in the Netherlands
are heterogeneous. The evidence base of current practice and the new guideline are discussed.