Long-term carbimazole pretreatment reduces the efficacy of radioiodine therapy

INTRODUCTION: Data from several studies suggest that pretreatment with antithyroid drugs (ATD) before (131)I increases the risk of treatment failure. This effect has been demonstrated more consistently with propylthiouracil than with carbimazole (CMZ) or methimazole (MMI). Men with Graves’ disease (GD) have a lower rate of remission with (131)I compared to women and the impact of long-term ATD pretreatment on the success of (131)I is unknown. The objective of our study was to compare the efficacy of fixed doses of radioiodine between patients with and without long-term CMZ pretreatment. MATERIALS AND METHODS: We performed a retrospective study on 335 male patients with GD treated with (131)I from 1998 to 2008. 148 patients had been pretreated with CMZ, and the remaining 187 patients received (131)I without pretreatment. We compared the success rate of a single dose of (131)I, between patients with and without long-term CMZ pretreatment. RESULTS: The success rate of a single dose of (131)I was significantly higher in patients without pretreatment than in patients who were pretreated with CMZ (91.4% vs. 82.3%, P = 0.01). The rate of hypothyroidism in the first 6 months after (131)I therapy was significantly higher in patients without pretreatment (55.1% vs. 44.6%, P = 0.05). There was also a trend for higher cumulative rate of hypothyroidism at last follow-up in nonpretreated patients (78.1% vs. 69.7%). CONCLUSION: Male patients with Graves’ hyperthyroidism pretreated with CMZ have lower efficacy with 131I therapy compared to nonpretreated patients. CMZ pretreatment given for a prolonged period reduces the efficacy of (131)I therapy.